Patent Publication Number: US-9424799-B2

Title: On-screen image adjustments

Description:
BACKGROUND 
     This specification relates to performing on-screen image adjustments, for example, to adjust colors of digital images by using color control tools overlaid on the digital images to be adjusted. 
     An image processing application can receive a request from a user associated with the application to modify a color of a portion of a digital image. For example, the image portion can represent a human face, a portion of sky, grass, and the like. In some cases, the user can request to modify the saturation of the image portion&#39;s color, in other cases the user can request to change the hue of the image portion. The image processing application configured to perform these and other user-requested color adjustments can provide the user respective color controls through which to receive user input of the desired color saturation, hue, etc. The respective color controllers can be laid out in a graphical user interface (GUI), associated with the image processing application, adjacent to a panel of the GUI configured to display the adjusted digital image, and optionally along with an additional panel configured to display the unadjusted digital image. Such a graphical user interface associated with the image processing application is typically presented to the user on a large computer display. 
     SUMMARY 
     Systems and techniques described in this specification can be used, among other ways, to intuitively and easily adjust colors in a digital image. In this fashion, users of image processing applications operated in accordance with the described technologies, among other potential benefits, can apply color effects, preset adjustments or both to digital images without having to know about color saturation, color temperature, hue or other notions of color science. Additionally, the described technologies optionally can be integrated in a non-intrusive manner in a GUI of an image processing application running on mobile devices, for which display real-estate tends to be at a premium. For example, the described technologies provide a color control tool that can be superimposed on a portion of the digital image selected by a user for color adjustment, such that the color control tool contains indicators of available color effects and preset adjustments. In this manner, the user can provide input selecting both a color effect and its magnitude to be applied by the image processing application to the selected image portion by using the color control tool superimposed on the image portion to be modified. Typically, each of the available color effects and preset adjustments represents a predefined combination that includes at least two color transformations. 
     In general, one aspect of the subject matter described in this specification can be implemented in methods that include the actions of presenting, within a graphical user interface (GUI), a digital image including a plurality of colors, and receiving user input selecting a color within the digital image. The methods further include the actions of displaying within the GUI, and superimposed on the digital image, a color control tool configured to cause change of the selected color within the digital image in accordance with user input specifying movement within the GUI. The color control tool includes a plurality of effect indicators, each indicating a color effect or preset adjustment from among a plurality of respective color effects and preset adjustments to be applied to the selected color in response to an associated predetermined movement within the GUI. Furthermore, the methods include actions of receiving via the color control tool user input specifying a direction of movement within the GUI relative to the plurality of effect indicators, and changing the selected color using a color effect or preset adjustment indicated by the effect indicator associated with the specified direction of movement. 
     The foregoing and other implementations can each optionally include one or more of the following features, alone or in combination. In some implementations, each of the plurality of effect indicators can include an associated new color indicator indicating a new color to be obtained when applying the color effect or preset adjustment to the selected color in response to the associated predetermined movement in the GUI. Each of the plurality of effect indicators further can include a label of the color effect or preset adjustment to be applied in response to the associated predetermined movement in the GUI. In other implementations, each of the plurality of effect indicators can include a label of the color effect or preset adjustment to be applied in response to the associated predetermined movement in the GUI, without including the associated new color indicator indicating the new color to be obtained when applying the color effect or preset adjustment to the selected color. 
     In some implementation, the methods can include the actions of updating the digital image display in real time to show a result of changing the selected color in response to the received user input via the color control tool. In some implementations, the user input received via the color control tool further specifies a length of the movement within the GUI relative to the plurality of effect indicators, such that a magnitude of the change in the selected color is determined based on the specified length of the movement. Changing the selected color using the color effect or preset adjustment indicated by the effect indicator associated with the specified direction of movement can be performed while the specified length of the movement is between first and second predefined lengths. For example, the methods can include the actions of indicating that the first predefined length of the specified movement has been reached by removing the plurality of effect indicators except for the effect indicator associated with the specified direction of movement. As another example, the methods can include the actions of indicating that the second predefined length of the specified movement has been reached by removing the effect indicator associated with the specified direction of movement. Further, prior to removing the effect indicator associated with the specified direction of movement, the methods can include the actions of gradually fading the displayed color control tool as the specified length of the movement increases from the first predefined length to the second predefined length. 
     Another aspect of the subject matter described in this specification can be implemented in methods that include the actions of displaying, within a GUI and superimposed on a digital image being manipulated, a color control tool configured to cause change of a selected color within the digital image in accordance with user input specifying movement within the GUI. The color control tool includes a plurality of new color indicators, each indicating a new color to which the selected color will change in response to an associated predetermined movement within the GUI. The methods also include the actions of receiving via the color control tool user input specifying a direction of movement within the GUI relative to the plurality of new color indicators, and changing the selected color to match the new color indicator associated with the specified direction of movement. 
     The foregoing and other implementations can each optionally include one or more of the following features, alone or in combination. In some implementations, the methods can include the actions of updating the digital image display in real time to show a result of changing the selected color to match the new color indicator associated with the received user input via the color control tool. In some implementations, the methods also can include the actions of receiving user input selecting the color to be changed using the color control tool, such that displaying the control tool is performed in response to the received user input selecting the color. In some implementations, the methods further can include the actions of detecting one or more colors of the digital image for which color effects and preset adjustments are available, and marking the detected one or more colors to indicate to the user that the marked one or more colors can be changed, such that the user selected color is from among the marked one or more colors. 
     In some implementations, for each one of the plurality of new color indicators, the new color indicated by the one new color indicator can be obtained from the selected color by applying an associated color effect or preset adjustment of a plurality of color effects and preset adjustments corresponding to the plurality of respective new color indicators. Each one of the plurality of color effects and preset adjustments can include two or more color transformations that are combined in an associated predefined proportion. The two or more color transformations combined in the associated predefined proportion can include either of gamma, luminance, saturation, contrast or brightness adjustments. 
     Other implementations of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods. A system of one or more computers can be so configured by virtue of software, firmware, hardware, or a combination thereof installed on the system that, in operation, cause the system to perform the actions. One or more computer programs can be so configured by virtue of having instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. 
     Another aspect of the subject matter described in this specification can be implemented in a system that includes a display device, at least one processor and storage configured to store instructions that, when executed by the processor, cause the system to perform operations including presenting, within a GUI on the display device, a digital image including a plurality of colors. The operations further include receiving user input selecting a color within the digital image, and displaying within the GUI, and superimposed on the digital image, a color control tool configured to cause change of the selected color within the digital image in accordance with user input specifying movement within the GUI. The color control tool includes a plurality of new color indicators, each indicating a new color to which the selected color will change in response to an associated predetermined movement within the GUI. 
     The foregoing and other implementations can each optionally include one or more of the following features, alone or in combination. In some implementations, the operations can further include receiving via the color control tool user input specifying a direction of movement within the GUI relative to the plurality of new color indicators, and changing the selected color to match the new color indicator associated with the specified direction of movement. Furthermore, the received user input selecting the color within the digital image can include an indication of an image pixel having the selected color, and changing the selected color can be performed only within a contiguous portion of the image including the indicated pixel. In some implementations, the displayed color indicator tool is superimposed on a portion of the image that includes the selected color. 
     In some implementations, the associated predetermined movement within the GUI, responsible for changing the selected color to the new color, can correspond to application of an associated color effect or preset adjustment to the selected color. In addition, the associated color effect or preset adjustment can include a predefined combination of two or more color adjustments. For example, the two or more color adjustments associated with the predefined combination are either of gamma, luminance, saturation, contrast, brightness or saturation adjustments. Additionally, the operations can include accessing, from among a plurality of color effects and preset adjustments stored on the storage, multiple color effects, preset adjustments or both applicable to the selected color. Further, the operations can include populating the color control tool with respective multiple new color indicators corresponding to the accessed multiple color effects, preset adjustments or both applicable to the selected color, and concurrently displaying a predefined quantity of the multiple new color indicators that populate the color control tool. Furthermore, the operations can include accessing, from among a plurality of color effects and preset adjustments stored on the storage, a predefined quantity of color effects, preset adjustments or both applicable to the selected color, and concurrently displaying the predefined quantity of multiple new color indicators corresponding to the accessed multiple color effects, preset adjustments or both applicable to the selected color. Moreover, the plurality of new color indicators can be distributed radially around a reference location, such that (i) a direction of the associated predetermined movement with respect to the reference location represents selection of the applied color effect or preset adjustment, and (ii) a length of the associated predetermined movement represents a magnitude of the applied color effect or preset adjustment. 
     Particular implementations of the subject matter described in this specification can be configured so as to realize one or more of the following potential advantages. A color adjustment utility enables an end-user to adjust the color of a digital image in an intuitive and visual manner, for example, without having to understand arcane color-theory notions such as hue or saturation (which tend to be non-intuitive and unfamiliar to most users.) In addition, the color adjustment utility can superimpose a color control tool on the digital image being manipulated, without having to dedicate a portion of the GUI associated with the color adjustment utility to the color control tool. The color control tool can include multiple new color indicators such that each one of the multiple new color indicators indicates a new color to which a color selected by the user will change in response to a user selection of the one of the multiple new color indicators. In this fashion, the user of the disclosed color adjustment utility can visualize, side-by-side with the selected color, output colors of multiple available color effects and preset adjustments. Hence, the color adjustment utility allows, among other things, the user to select, in a visual and intuitive way, a desired new color from among the multiple new colors indicated by the color control tool. 
     Optionally, upon receiving the user selected new color to which the user selected color will be changed, the color adjustment utility can remove from view unselected new color indicators of the color control tool. By doing so, the color adjustment utility can reduce clutter and increase a fraction of the manipulated digital image that is unobstructed by the color control tool. In addition, as it changes from the original user-selected color to the new user-selected color, the color adjustment utility optionally can cause the new color indicator associated with the user selected new color to gradually fade out-of-view. In this manner, the color adjustment utility can present to the viewer a manipulated digital image that is essentially unobstructed by the color control tool. 
     Details of one or more implementations of the described subject matter are set forth in the accompanying drawings and the description below. Other features, aspects, and potential advantages will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. 
         FIG. 1  illustrates an example of a system that includes an on-screen image adjustment environment. 
         FIGS. 2A-2J  show aspects of an on-screen image adjustment environment. The  FIGS. 2A-2J  are presented in color. 
         FIG. 3  shows an example of a method for applying color effects within an on-screen image adjustment environment. 
         FIG. 4  is a block diagram of an example of a mobile device operated according to the technologies described above in connection with  FIGS. 1-3 . 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example of a system  100  that includes an on-screen image adjustment environment. The system  100  can be implemented as part of an image processing application executed by a computer system. The computer system can be a mobile device  102 . Examples of mobile devices that can be part of the system  100  are cellular telephones, smartphones, personal digital assistants (PDAs), mobile computers (e.g., tablet computers, laptops, and the like), digital cameras, media players or combinations of these. The system  100  can include a graphical user interface (GUI) that displays a digital image  105  including a plurality of colors. The GUI can provide controls and indicators to be used by a user associated with the image processing application for specifying how to process the displayed image. The system  100  can also include a plurality of utilities that carry out under-the-hood processing of the displayed image. 
     The plurality of utilities of the system  100  can include an on-screen image adjustment utility  110 . The on-screen image adjustment utility  110  can access the digital image  105  displayed by the mobile device  102  and can receive a sequence of instructions for processing the displayed image  105 . The sequence of instructions can begin with a selection of a color  122  of the displayed image  105 , can continue with one or more selections of color effects or preset adjustments or both  132  to be applied to the selected color, and can end with an instruction to complete  142  the application of the selected effect to the selected color. The user can enter the requests  122 ,  132  and  142  via multi-touch gestures or keyboard/mouse instructions. In general, the instructions received by the on-screen image adjustment utility  110  are processed by various modules therein to allow a user associated with the system  100  to evaluate one or more color changes of the displayed image  105  prior to committing the applied color effects, preset adjustments or both to the final, adjusted image  105 ″. In  FIG. 1 , these various modules include an effect proponent module  125  configured to propose color effects and preset adjustments that are applicable to the selected color of the image  105  and an effect applicator module  135  configured to apply to the displayed image  105  one or more of the color effects, preset adjustments or both selected by the user from among the proposed color effects and preset adjustments. Aspects relating to the functionality of the on-screen image adjustment utility  110 &#39;s modules are illustrated in  FIGS. 2A-2J . For example, an image processing application  200  described below in connection with  FIGS. 2A-2J  can correspond to the system  100 . 
     In  FIG. 1 , the displayed digital image  105  includes a first image portion  107  having a first color, and another image portion  109  having a second color. In some implementations, both of the first and second image portions can be contiguous (as shown in  FIG. 1 .) For example, the first image portion  107  can correspond to a person&#39;s skin and the second image portion  109  can represent grass. In other implementations, the first image portion can be contiguous, and the second image portion can be dis-contiguous. In an example of a digital image  205  illustrated in  FIG. 2A , the first (contiguous) image portion can correspond to the Arc de Triomphe, and the second (dis-contiguous) image portion corresponds to the sky, visible around and within the Arc. In some other implementations, both first and second image portions can be dis-contiguous. For example, in an image of FC Barcelona&#39;s home jersey, the first portion of the image can represent the cherry stripes of the jersey, and the second portion of the image can represent the navy stripes of the jersey. In general, a color corresponding to one of the image portions can be selected by a user of the image processing application to be improved/enhanced. Accordingly, the user can use the on-screen image adjustment utility  110  to output a visually pleasing digital image  105 ″ either by modifying the selected color within the entire corresponding image portion (whether the latter is contiguous or not), or by modifying the selected color only within a contiguous part of the corresponding image portion, such that the part includes an image location at which the user has selected the color. 
     The on-screen image adjustment utility  110  can access the displayed digital image  105  and can receive a user selection of a color  122  within the digital image  105 . The selected color corresponds to the red (R), green (G) and blue (B) values at an image location  120  specified by the user as part of the received color selection  122 . In some implementations, the RGB values corresponding to the selected color can represent the RGB values associated with the pixel at the specified image location  120 . In other implementations, the RGB values corresponding to the selected color can represent average RGB values over a predetermined number of pixels adjacent to the specified image location  120 . In  FIG. 2A , the user can select a sky blue color via a multi-touch gesture  222  (e.g., a single tap) at a location  220  contained in a portion of the image  205  associated with the sky. Optionally, the GUI associated with the image processing application  200  can include color swatches to indicate the selected sky blue color  210  and its corresponding blue hue  212 , respectively, at the image point  220  specified by the user via the color selection  222 . Typical color adjustments can modify the hue of (a portion of) the image. The hue-approach to color adjustments can be unintuitive, because sometimes the underlying hue does not even resemble the color the user is trying to adjust. A reason for the discrepancy between a color and the underlying hue(s) is that hues represent saturated colors, as opposed to more muted, true colors that are typically depicted in an image  205 . The muted true colors tend to be formed as combinations of several colors, e.g., browns, tans, etc. For example, in  FIG. 2I , the user can select a tan color via a multi-touch gesture  230 ′ (e.g., a single tap) at a location  220 ′ contained in a portion of the image  205  associated with the Arc de Triomphe. In this case, the color swatches displayed in the GUI associated with the image processing application  200  indicate the tan color  210 ′ and its corresponding orange hue  212 ′, respectively, at the image point  220 ′ specified by the user via the color selection  230 ′. 
     Referring again to  FIG. 1 , upon receiving the color selection  122 , the effect proponent module  125  can access a data store  126  configured to store a plurality of color effects and preset adjustments  128  to determine, from among the latter, color effects or preset adjustments or both that are applicable to the user selected color. In some implementations, the data store  128  can be local to the on-screen image adjustment utility  110 . For example, the data store  128  can be stored on memory of the mobile device  102 , and can be directly accessed by the effect proponent module  125 . In some implementations, the data store  128  can be stored at a network location, e.g., in the cloud, and can be accessed by the effect proponent module  125  via network connections maintained by the mobile device  102 . In either of these implementations, the data store  126  can be an XML file, a relational database, or the like. 
     Each of the color effects and of the preset adjustments  128  stored on the data store  126  represents a predefined combination that includes at least two color transformations. The color transformations included in a given combination and their relative proportions (weights) within the given combination depend on whether the effect or preset adjustment associated with the given combination is generic or color specific. A generic color effect or preset adjustment represents a predefined combination of color transformations that is applicable to any input color. When the generic color effect or preset adjustment is applied to an input color, e.g., the color selected by the user, the transformations combined in the generic effect or preset adjustment are being applied within a predefined, narrow range centered on a hue associated with the input color, e.g., ±3 degrees (or about ±1%) of the 360 degrees of hue space. In this fashion, the generic effect or preset adjustment modifies the input color and some (similar) colors near the input color. Examples of generic effects and preset adjustments are described below in connection with  FIGS. 2B and 2F . 
     A color specific effect or preset adjustment includes color transformations combined in a way that is optimized for a specific color. Examples of specific colors are sky blue color, skin color, grass color, and the like. English names of these and other colors correspond to accepted hexadecimal or decimal RGB triplet values. For instance, the colors in the range from cyan to midnight blue and their respective hex and decimal RGB triplets are listed in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 RGB triplets and equivalent English color names 
               
            
           
           
               
               
               
               
            
               
                   
                 Blue/Cyan colors 
                 Hex code RGB 
                 Decimal code RGB 
               
               
                   
                   
               
               
                   
                 Aqua 
                 00 FF FF 
                 0 255 255 
               
               
                   
                 Cyan 
                 00 FF FF 
                 0 255 255 
               
               
                   
                 Light Cyan 
                 E0 FF FF 
                 224 255 255 
               
               
                   
                 Pale Turquoise 
                 AF EE EE 
                 175 238 238 
               
               
                   
                 Aquamarine 
                 7F FF D4 
                 127 255 212 
               
               
                   
                 Turquoise 
                 40 E0 D0 
                 64 224 208 
               
               
                   
                 Medium Turquoise 
                 48 D1 CC 
                 72 209 204 
               
               
                   
                 Dark Turquoise 
                 00 CE D1 
                 0 206 209 
               
               
                   
                 Cadet Blue 
                 5F 9E A0 
                 95 158 160 
               
               
                   
                 Steel Blue 
                 46 82 B4 
                 70 130 180 
               
               
                   
                 Light Steel Blue 
                 B0 C4 DE 
                 176 196 222 
               
               
                   
                 Powder Blue 
                 B0 E0 E6 
                 176 224 230 
               
               
                   
                 Light Blue 
                 AD D8 E6 
                 173 216 230 
               
               
                   
                 Sky Blue 
                 87 CE EB 
                 135 206 235 
               
               
                   
                 Light Sky Blue 
                 87 CE FA 
                 135 206 250 
               
               
                   
                 Deep Sky Blue 
                 00 BF FF 
                 0 191 255 
               
               
                   
                 Dodger Blue 
                 1E 90 FF 
                 30 144 255 
               
               
                   
                 Cornflower Blue 
                 64 95 ED 
                 100 149 237 
               
               
                   
                 Royal Blue 
                 41 69 E1 
                 65 105 225 
               
               
                   
                 Blue 
                 00 00 FF 
                 0 0 255 
               
               
                   
                 Medium Blue 
                 00 00 CD 
                 0 0 205 
               
               
                   
                 Dark Blue 
                 00 00 8B 
                 0 0 139 
               
               
                   
                 Navy 
                 00 00 80 
                 0 0 128 
               
               
                   
                 Midnight Blue 
                 19 19 70 
                 25 25 112 
               
               
                   
                   
               
            
           
         
       
     
     Moreover, color specific effects to change sky blue are described below in connection with  FIG. 2B . These sky blue specific effects are configured to transform the hue, saturation, and luminance values of the sky blue color by applying a gamma function and a luminance function to the sky blue color. For instance, a combination of (i) a transformation to increase gamma of the sky blue portion of the digital image, and (ii) a transformation to decrease luminance of the same image portion has the desired effect of making a deeper and more moody sky, as described below in connection with  FIGS. 2B-2C . 
     Once it accessed the color effects and preset adjustments  128  stored in the data store  126 , the effect proponent  125  can determine which ones of the foregoing are applicable to the selected color. For example, the effect proponent  125  can determine that all generic color effects and preset adjustments from among the stored color effects and preset adjustments  128  can be applied to the selected color. As another example, the effect proponent  125  can identify, from among the stored color effects and preset adjustments  128 , the ones that are specific to and hence are applicable to the user selected color. As such, if the color, selected via the color selection  122  specified by the user at location  120 , is skin color, then the effect proponent  125  can determine that color effects and preset adjustments stored in data store  126  that are applicable to the selected skin color include the generic ones and the skin color effects, preset adjustments or both. 
     Once it determines the color effects, preset adjustments or both applicable to the selected color, the effect proponent  125  can display superimposed on the digital image  105 , a color control tool  130 * configured to cause change of the selected color within the digital image  105  in accordance with user input specifying movement  132  within the GUI. As shown in the inset  130  of  FIG. 1 , the color control tool  130 * can include “n” effect indicators  138 - 1 ,  138 - 2 , . . . ,  138 - j , . . . ,  138 - n , each one indicating a color effect or preset adjustment, from among the respective determined color effects, preset adjustments or both, “1”, “2”, . . . , “j”, . . . , “n”, to be applied to the selected color in response to an associated predetermined movement  132  within the GUI. The “n” effect indicators  138 - 1 ,  138 - 2 , . . . ,  138 - j , . . . ,  138 - n , that populate the color control tool  130 * can be distributed radially around a reference color indicator R- 138 . The reference color indicator R- 138  can be common among the “n” effect indicators  138 - 1 ,  138 - 2 , . . . ,  138 - j , . . . ,  138 - n , and indicates a color at the user specified image location  120  to be modified by applying one of the color effects, preset adjustments or both “1”, “2”, . . . , “j”, . . . , “n”, in response to the associated predetermined movement  132  within the GUI. A direction of the associated predetermined movement  132  is represented in the inset  130  by a directed ray associated with the one effect. 
     In some implementations, “n” represents the total number of color effects, preset adjustments or both, 1”, “2”, . . . , “j”, . . . , “n”, that are determined by the effect proponent  125  to be applicable to the user selected color. In other implementations, the “n” effect indicators that populate the color control tool  130 * represent a predefined maximum quantity of effect indicators corresponding to “n” of “N” color effects, preset adjustments or both, 1”, “2”, . . . , “n”, . . . , “N”, that are determined by the effect proponent  125  to be applicable to the user selected color. In  FIG. 2A , the image processing application  200  superimposes a color control tool  270  on the digital image  205 , in response to a color selection  222 , specified by the user at image point  220 . The 4-point color control tool  270  includes n=4 effect indicators corresponding to 1-4 of N=8 color effects, preset adjustments or both that are applicable to the sky blue color specified by the user selection  222 . Moreover, the user can toggle display of the “n” effect indicators and the remaining “N-n” effect indicators for the color control tool  130 *. In  FIG. 2E , the user can change display of the 1-4 of 8 effect indicators to display of the 5-8 of 8 effect indicators of the 4-point color control tool  270  by using a multi-touch gesture (e.g., a double tap  240 ) at the user specified location  220 . The instance of the 4-point color control indicator  270  that includes the 5-8 of 8 effect indicators is referenced in  FIG. 2E  as the 4-point color control tool  280 . 
     Referring again to  FIG. 1 , in some implementations, each one of the “n” effect indicators (e.g.,  138 - j ) can include an associated new color indicator T- 138 - j  that indicates a new (or target) color to be obtained when applying the associated color effect or preset adjustment “j” to the selected color, in response to the associated predetermined movement  132  in the GUI. In this manner, the new color indicator T- 138 - j  can guide the user in selecting the effect “j” to be applied to the selected color at the image location  120  (the latter color being indicated by a reference color indicator R- 138  displayed side-by-side to the new color indicator T- 138 - j , as part of the same effect indicator  138 - j .) Optionally, each one of the “n” effect indicators can further include a label of the associated effect “j” to be applied in response to the associated predetermined movement in the GUI. In other implementations, each of one the “n” effect indicators (e.g.,  138 - j ) can only include a label of the associated effect “j” to be applied in response to the associated predetermined movement  132  in the GUI, without including a new color indicator. 
       FIG. 2B  shows a close-up of the 4-point color control tool  270 . Respective instances  270  and  270 ′ of this 4-point color control tool are superimposed in  FIGS. 2A and 2I  by the image processing application  200  on the digital image  205 , in response to the color selections  222  and  222 ′, specified by the user at image points  220  and  220 ′. The 4-point color control tool  270  includes four effect indicators  272 ,  274 ,  276  and  278 . The effect indicator  272  corresponds to a generic color effect that changes an input color to a deeper color. The effect indicator  272  includes a reference color indicator  271  configured to indicate the input color, or the color to be changed to a deeper color. In  FIG. 2A , the input color is the sky blue color specified by the user via the color selection  222  at the image location  220 . In  FIG. 2I , the input color is the tan color of the Arc de Triomphe specified by the user via the color selection  222 ′ at the image location  220 ′. The effect indicator  272  further includes a new color indicator  272 - i  configured to indicate the (target) deeper color obtained by changing the input color (indicated by the reference color indicator  271 ) when the user moves the effect indicator  272  upwards, in the direction indicated by the arrow associated with the numerical reference  272 . As shown in Table 2, the deeper color effect associated with the effect indicator  272  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by increasing gamma and decreasing the luminance. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  272  includes an effect label  272 -I to spell out that the input color will be changed to a deeper color by moving the effect indicator  272 . 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Effect indicators of 4-point color control tool 270 
               
            
           
           
               
               
               
               
            
               
                 Reference 
                 Name of color 
                   
                   
               
               
                 of effect 
                 effect or preset 
                 Combination of 
               
               
                 indicator 
                 adjustment 
                 transformations 
                 Type 
               
               
                   
               
               
                 272 
                 Deeper color 
                 Increase gamma + 
                 Generic 
               
               
                   
                   
                 decrease luminance 
               
               
                 276 
                 Paler color 
                 Decrease gamma + 
                 Generic 
               
               
                   
                   
                 increase luminance 
               
               
                 274 
                 Darker color 
                 Decrease luminance + 
                 Generic 
               
               
                   
                   
                 increase saturation 
               
               
                 278 
                 Lighter color 
                 Increase luminance + 
                 Generic 
               
               
                   
                   
                 decrease saturation 
               
               
                   
               
            
           
         
       
     
     The effect indicator  276  corresponds to a generic color effect that changes an input color to a paler color. The color effect associated with the effect indicator  276  is complementary to the color effect associated with the effect indicator  272 , and in this example, the complementary effect indicators  272  and  276  are laid out along diametrically opposed directions within the 4-point color control tool  270 . The effect indicator  276  includes the reference color indicator  271  configured to indicate the input color, or the color to be changed to a paler color. The effect indicator  276  further includes a new color indicator  276 - i  configured to indicate the (target) paler color obtained by changing the input color (indicated by the reference color indicator  271 ) when the user moves the effect indicator  276  downwards, in the direction indicated by the arrow associated with the numerical reference  276 . As shown in Table 2, the paler color effect associated with the effect indicator  276  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by decreasing gamma and increasing the luminance. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  276  includes an effect label  276 -I to spell out that the input color will be changed to a paler color by moving the effect indicator  276 . 
     The effect indicator  274  corresponds to a generic color effect that changes an input color to a darker color. The effect indicator  274  includes the reference color indicator  271  configured to indicate the input color, or the color to be changed to a paler color. The effect indicator  274  further includes a new color indicator  274 - i  configured to indicate the (target) darker color obtained by changing the input color (indicated by the reference color indicator  271 ) when the user moves the effect indicator  274  rightwards, in the direction indicated by the arrow associated with the numerical reference  274 . As shown in Table 2, the darker color effect associated with the effect indicator  274  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by decreasing the luminance and increasing the saturation. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  274  includes an effect label  274 -I to spell out that the input color will be changed to a darker color by moving the effect indicator  274 . 
     The effect indicator  278  corresponds to a generic color effect that changes an input color to a lighter color. The color effect associated with the effect indicator  278  is complementary to the color effect associated with the effect indicator  274 , and in this example, the complementary effect indicators  274  and  278  are laid out along diametrically opposed directions within the 4-point color control tool  270 . The effect indicator  278  includes the reference color indicator  271  configured to indicate the input color, or the color to be changed to a lighter color. The effect indicator  278  further includes a new color indicator  278 - i  configured to indicate the (target) lighter color obtained by changing the input color (indicated by the reference color indicator  271 ) when the user moves the effect indicator  278  leftwards, in the direction indicated by the arrow associated with the numerical reference  278 . As shown in Table 2, the lighter color effect associated with the effect indicator  278  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by increasing the luminance and decreasing the saturation. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  278  includes an effect label  278 -I to spell out that the input color will be changed to a darker color by moving the effect indicator  278 . 
       FIG. 2F  shows a close-up of the 4-point color control tool  280 . The 4-point color control tool  280 , represents another instance of the 4-point color control tool  270 , and is superimposed in  FIG. 2E  by the image processing application  200  on the digital image  205 , in response to a user input  240 . The 4-point color control tool  280  includes four effect indicators  282 ,  284 ,  286  and  288 . The effect indicator  282  corresponds to a color specific effect that changes a sky blue color to a more bluish color. The effect indicator  282  includes a reference color indicator  281  configured to indicate the input sky blue color to be changed to a more bluish color. In  FIG. 2E , the input color can be the previously changed sky blue color at the image location  220  obtained by applying the color effects  272  and  274  specified by the user via the effect selections  232  and  234 , respectively. The effect indicator  282  further includes a new color indicator  282 - i  configured to indicate the (target) more bluish color obtained by changing the sky blue color (indicated by the reference color indicator  281 ) when the user moves the effect indicator  282  upwards, in the direction indicated by the arrow associated with the numerical reference  282 . As shown in Table 3, the more bluish color effect associated with the effect indicator  282  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by increasing the hue value and increasing the saturation. The increase in hue value is capped to prevent wrap-around of the hue wheel. In this case, the blue hue of the sky blue color can be replaced with the neighboring indigo hue. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  282  includes an effect label  282 -I to spell out that the input color will be changed to a more bluish color by moving the effect indicator  282 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Effect indicators of 4-point color control tool 280 
               
            
           
           
               
               
               
               
            
               
                 Reference 
                 Name of color 
                   
                   
               
               
                 of effect 
                 effect or preset 
                 Combination of 
               
               
                 indicator 
                 adjustment 
                 transformations 
                 Type 
               
               
                   
               
               
                 282 
                 More bluish 
                 Increase hue value 
                 Sky blue 
               
               
                   
                 color 
                 (e.g., replacing the blue 
                 specific 
               
               
                   
                   
                 hue with an indigo hue) + 
               
               
                   
                   
                 Increase saturation 
               
               
                 286 
                 More cyanish 
                 Decrease hue value 
                 Sky blue 
               
               
                   
                 color 
                 (e.g. replacing the blue 
                 specific 
               
               
                   
                   
                 hue with a cyan hue) + 
               
               
                   
                   
                 Increase saturation 
               
               
                 284 
                 More color 
                 Increase hue value + 
                 Generic 
               
               
                   
                   
                 increase color 
               
               
                   
                   
                 saturation + decrease 
               
               
                   
                   
                 luminance 
               
               
                 288 
                 Less color 
                 Decrease hue value + 
                 Generic 
               
               
                   
                   
                 increase color 
               
               
                   
                   
                 saturation + decrease 
               
               
                   
                   
                 luminance 
               
               
                   
               
            
           
         
       
     
     The effect indicator  286  corresponds to a color specific effect that changes a sky blue color to a more cyanish color. The color effect associated with the effect indicator  286  is complementary to the color effect associated with the effect indicator  282 , and in this example, the complementary effect indicators  282  and  286  are laid out along diametrically opposed directions within the 4-point color control tool  280 . The effect indicator  286  includes the reference color indicator  281  configured to indicate the input sky blue color, or the color to be changed to a more cyanish color. Note that the reference color indicator  281  is common among the effect indicators  282 ,  284 ,  286  and  288 . The effect indicator  286  further includes a new color indicator  286 - i  configured to indicate the (target) more cyanish color obtained by changing the input sky blue color (indicated by the reference color indicator  281 ) when the user moves the effect indicator  286  downwards, in the direction indicated by the arrow associated with the numerical reference  286 . As shown in Table 3, the more cyanish color effect associated with the effect indicator  286  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by decreasing the hue value and increasing the saturation. The decrease in hue value is capped to prevent wrap-around of the hue wheel. In this case, the blue hue of the sky blue color can be replaced with the neighboring cyan hue. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  286  includes an effect label  286 -I to spell out that the input color will be changed to a more cyanish color by moving the effect indicator  286 . 
     The effect indicator  284  corresponds to a generic color effect that adds more color to an input color, e.g., changes the input color to a more saturated color. The effect indicator  284  includes the reference color indicator  281  configured to indicate the input color, or the color to be changed to a more saturated color. The effect indicator  284  further includes a new color indicator  284 - i  configured to indicate the (target) more saturated color obtained by changing the input color (indicated by the reference color indicator  281 ) when the user moves the effect indicator  284  rightwards, in the direction indicated by the arrow associated with the numerical reference  284 . As shown in Table 3, the more color effect associated with the effect indicator  284  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by increasing the hue value, increasing the saturation and decreasing the luminance. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  284  includes an effect label  284 -I to spell out that the input color will be changed to a more saturated color by moving the effect indicator  284 . 
     The effect indicator  288  corresponds to a generic color effect that subtracts color from an input color, e.g., changes the input color to a less saturated color. The color effect associated with the effect indicator  288  is complementary to the color effect associated with the effect indicator  284 , and in this example, the complementary effect indicators  284  and  288  are laid out along diametrically opposed directions within the 4-point color control tool  280 . The effect indicator  288  includes the reference color indicator  281  configured to indicate the input color, or the color to be changed to a less saturated color. The effect indicator  288  further includes a new color indicator  288 - i  configured to indicate the (target) less saturated color obtained by changing the input color (indicated by the reference color indicator  281 ) when the user moves the effect indicator  288  leftwards, in the direction indicated by the arrow associated with the numerical reference  288 . As shown in Table 3, the less color effect associated with the effect indicator  288  is based on a combination of transformations and adjustments to be applied to the input color. An RGB triplet value corresponding to the input color is first transformed to obtain an equivalent hue-saturation-luminance (HSL) triplet value. The image pixels corresponding to the obtained HSL triplet value are further adjusted by decreasing the hue value, decreasing the saturation and decreasing the luminance. The adjusted HSL triplet value of the image pixels can be further transformed to obtain the adjusted RGB triplet value. Moreover, the effect indicator  288  includes an effect label  288 -I to spell out that the input color will be changed to a less saturated color by moving the effect indicator  288 . 
     The combinations of transformations and adjustments described above in connection with Tables 2 and 3 represent potential implementations or approaches to obtain the color effects or preset adjustments described in this specification. Other algorithms can be used to obtain the foregoing or other color effects or preset adjustments. 
     Referring again to  FIG. 1 , the on-screen image adjustment utility  110  can receive, via the color control tool  130 *, user input specifying a direction of movement  132  within the GUI relative to the “n” effect indicators of the color control tool  130 *. The user can specify the direction of movement  132  via a touch-swipe gesture or via either a touch- or a cursor-drag gesture along a radial direction, within the color control tool  130 *, associated with one of the “n” effect indicators (e.g., the effect indicator  138 - j .) Upon receipt of the direction of movement  132  specifying the effect indicator  138 - j , the effect applicator module  135  can change the selected color using the color effect or preset adjustment “j” indicated by the specified effect indicator  138 - j . Additionally, the on-screen image adjustment utility  110  can update the display of the digital image  105 ′ in real time to show a result of changing the selected color to match the new color indicator T- 138 - j  associated with effect indicator  138 - j  specified by the user via the color control tool  130 *. 
     In some implementations, the effect applicator  135  can change the selected image color in all portions of the image  105  having the same color as the specified image point  120 . In the example illustrated in  FIG. 2C , the deeper sky blue effect associated with the effect indicator  272  can be applied to portions of the sky around the Arc de Triomphe and inside the Arc. In other implementations, the changes to the selected image color can be applied by the effect applicator  135  only to the portion of the image  105  that includes the specified image point  120 . In the example illustrated in  FIG. 2C , the deeper sky blue effect associated with the effect indicator  272  can be applied to a first portion of the sky around the Arc de Triomphe that includes the specified image point  220 , but not to a second portion of the sky inside the Arc that is dis-contiguous from the first portion. 
     In some implementations, if the received user input is a swipe gesture  132  in the direction of the effect indicator  138 - j , the effect applicator  135  can change the selected color by applying the entire (e.g., 100% or a maximum predefined magnitude of the color effect or preset adjustment “j”, and can display the changed color as part of the adjusted digital image  105 ′, in real time. 
     In other implementations, if the user input is a drag gesture  132  in the direction of the effect indicator  138 - j , the effect applicator  135  can change the selected color by gradually applying the color effect or preset adjustment “j”, in real time, as the length of the drag gesture  132  increases between first and second predefined lengths. In this manner, the application of the color effect or preset adjustment “j” can start only once the length of the drag gesture  132  exceeds the first predefined length. While the length of the drag gesture  132  increases beyond the first predefined length, a magnitude of the change in the selected color also increases based on the current length of the drag gesture  132 , up to a maximum predefined magnitude of the color effect or preset adjustment “j”. The latter corresponds to the second predefined length of the drag gesture  132 . No additional change is being applied to the selected color by the effect applicator  135  when the length of the drag gesture  132  increases beyond the second predefined length. 
     Optionally, the on-screen image adjustment utility  110  can indicate that the first predefined length of the drag gesture  132  has been reached by removing at least some of the “n” effect indicators and retaining the effect indicator  138 - j  associated with the specified direction of the drag gesture  132 . Further, the on-screen image adjustment utility  110  can indicate that the second predefined length of the drag gesture  132  has been reached by removing the effect indicator  138 - j  associated with the specified direction of the drag gesture  132 . Moreover, prior to removing the effect indicator  138 - j  associated with the specified direction of drag gesture  132 , the on-screen image adjustment utility  110  can gradually fade the effect indicator  138 - j  as the specified length of the drag gesture  132  increases from the first predefined length to the second predefined length. By gradually removing out-of-view portions of the color control tool  130 *, e.g., initially the effect indicators that are different from the specified effect indicator, and later even the specified effect indicator, the on-screen image adjustment utility  110  can reduce the intrusiveness of the color control tool  130 *. 
     As described above in connection with  FIG. 2A , the image processing application  200  can superimpose the 4-point color control tool  270  on the digital image  205 , in response to the sky blue color selection  222 , specified by the user at the image point  220 , e.g., via a single-tap gesture. The 4-point color control tool  270 , and its effect indicators are described above in connection with  FIG. 2B . In  FIG. 2C , the user can drag  232  the effect indicator  272  upward in the GUI of the image processing application  200 . In some implementations, in response to the received drag gesture  232  selecting the effect indicator  272 , the image processing application  200  can remove from the 4-point color control tool  270  (superimposed on the image  205  in  FIG. 2A ) the effect indicators corresponding to the darker and lighter color effects. In this manner, the 4-point color control tool  270  can convert into a 2-point color control tool that retains only the selected effect indicator  272  corresponding to the deeper color effect and the effect indicator corresponding to the complementary, paler color effect. By doing so, the image processing application  200  can reduce clutter and increase a fraction of the image  205  that is unobstructed by the full 4-point color control tool  270 . 
     In other implementations, in response to the received drag gesture  232  selecting the effect indicator  272 , the image processing application  200  can remove from the 4-point color control tool  270  (superimposed on the image  205  in  FIG. 2A ) the (horizontal) effect indicators corresponding to the darker and lighter color effects, and the (vertical) effect indicator corresponding to the paler color effect. In this manner, the 4-point color control tool  270  can convert into a 1-point color control tool that retains only the selected effect indicator  272  corresponding to the deeper color effect, in the example illustrated in  FIG. 2C . Such a 1-point color control tool would just show the direction of the drag gesture  232 , but would not show the opposite direction. In this fashion, if the user applies a drag-down gesture after applying a drag-up gesture, the color control tool can switch either to a 1-point down-direction control or to a 2-point vertical-direction control. 
     Also in response to the received drag gesture  232  selecting the effect indicator  272 , the image processing application  200  can change the selected sky blue color to a deeper sky blue color that matches the new color indicator  272 - i  shown in  FIGS. 2A-2B . The changed, deeper sky blue color of the image  205  can be displayed by the image processing application  200 , in real time, while the user performs the drag gesture  232 . The fraction of the change from the selected color (displayed in the reference color indicator  271 ) to the deeper sky blue color indicated by the new color indicator  272 - i  is proportional to the length of the upwards drag gesture  232 . 
     Furthermore, as the user drags upward  232  the effect indicator  272 , the image processing application  200  causes the 2-point color control tool to gradually fade out-of-view, and removes it completely after the effect indicator  272  has been dragged by a predetermined vertical distance from the specified point  220 , e.g., when the changed, deeper sky blue color matches the new color indicator  272 - i  associated with the 4-point color control tool  270  depicted in  FIGS. 2A-2B . By doing so, the image processing application  200  can further reduce clutter and present to the viewer the image  205  that is unobstructed by the 2-point color control tool associated with the effect indicator  272 . 
     Upon receiving from the user the drag gesture  232  selecting the deeper color effect associated with the effect indicator  272 , and prior to changing the selected color in accordance with the selected deeper color effect, the image processing application  200  can store the RGB values  216  corresponding to the selected color at the specified image location  220 . In some implementations, the stored RGB values  216  can be displayed in the GUI associated with the image processing application  200 . By storing the RGB values  216  corresponding to the selected color prior to applying the selected effect or preset adjustment, the image processing application  200  can undo a color change in response to a user input received via a control  214  displayed on the GUI associated with the image processing application  200 . In addition to storing the RGB values  216 , the image processing application also can store the direction and magnitude of the drag gesture  232 . The stored information enables a user to effectively and efficiently modify previous edits. For instance, the user can reselect the image location  220  and continue adjusting, rather than having to apply new color effects or preset adjustments on top of the previously applied one(s). 
     Referring again to  FIG. 1 , the on-screen image adjustment utility  110  can receive a user input  142  requesting to return back to adjusting the color at the specified image point  120 . For example, the user can request to reselect the previously selected effect. In this case, the effect applicator  135  can apply the reselected effect to the previously changed color. As another example, the user can request to select another effect different from the previously selected effect. In this case, the effect applicator  135  can apply the other selected effect to the previously changed color. In addition, the request  142  received from the user can include selection of another color at another specified point  120 ′. The effect proponent  125  can display superimposed on the digital image  105  another color control tool  130 ′ including “k” effect indicators corresponding to color effects or preset adjustments or both applicable to the other selected color associated with the specified point  120 ′, where k≠n. Once the on-screen image adjustment utility  110  receives user selection  132  of an applicable color effect or preset adjustment to apply to the other selected color, the effect applicator  135  can change the other selected color in accordance with the user selected color effect or preset adjustment. 
     In some implementations, the on-screen image adjustment utility  110  can apply multiple user selected color effects or preset adjustments or both, whether to a single color or to two or more different colors, in an additive manner with respect to the digital image  105 . In other implementations, the on-screen image adjustment utility  110  can apply multiple user selected color effects or preset adjustments or both to respective multiple colors of the digital image in an additive manner with respect to the digital image. Additionally, the on-screen image adjustment utility  110  can apply the multiple user selected color effects or preset adjustments or both to a single color of the digital image in substitutive manner with respect to the digital image  105  (by replacing the previously applied color effect or preset adjustment with the currently applied color effect or preset adjustment.) 
     Returning to the examples illustrated in  FIGS. 2A and 2C , after applying the deeper color effect corresponding to the effect indicator  272  selected by the user with the drag gesture  232 , the image processing application  200  can receive another request  222  from the user (e.g., via a single-tap gesture) to superimpose the 4-point color control tool  270  at the image location  220 , as illustrated in  FIG. 2A . At that time, the user can drag  234  the effect indicator  274  rightward in the GUI of the image processing application  200 , as shown in  FIG. 2D . In response to the received drag gesture  234  selecting the effect indicator  274 , the image processing application  200  can remove from the 4-point color control tool  270  (superimposed on the image  205  in  FIG. 2A ) the effect indicators corresponding to the deeper and paler color effects. In this manner, the 4-point color control tool  270  can convert into a 2-point color control tool that retains only the selected effect indicator  274  corresponding to the darker color effect and the effect indicator corresponding to the complementary, lighter color effect. 
     Also in response to the received drag gesture  234  selecting the effect indicator  274 , the image processing application  200  can change the selected sky blue color to a darker sky blue color that matches the new color indicator  274 - i  shown in  FIGS. 2A-2B . The changed darker sky blue color of the image  205  can be displayed by the image processing application  200  in real time, while the user performs the drag gesture  234 . The fraction of the change from the selected color (displayed in the reference color indicator  271 ) to the darker sky blue color indicated by the new color indicator  274 - i  is proportional to the length of the rightward drag gesture  234 . 
     Furthermore, as the user drags rightward  234  the effect indicator  274 , the image processing application  200  causes the 2-point color control tool to gradually fade out-of-view and removes it completely after the effect indicator  274  has been dragged by a predetermined horizontal distance from the specified point  220 , e.g., when the changed darker sky blue color matches the new color indicator  274 - i  associated with the 4-point color control tool  270  depicted in  FIGS. 2A-2B . 
     After applying the darker color effect corresponding to the effect indicator  274  selected by the user with the drag gesture  234 , the image processing application  200  can receive another request  240  from the user (e.g., via a double-tap gesture) to superimpose the color control tool  280  at the image location  220 , as illustrated in  FIG. 2E . The 4-point color control tool  280 , and its effect indicators are described above in connection with  FIG. 2F . In  FIG. 2G , the user can drag  242  the effect indicator  282  upward in the GUI of the image processing application  200 . In response to the received drag gesture  242  selecting the effect indicator  282 , the image processing application  200  can remove from the 4-point color control tool  280  (superimposed on the image  205  in  FIG. 2E ) the effect indicators corresponding to the color effects providing more or less color. In this manner, the 4-point color control tool  280  can convert into a 2-point color control tool that retains only the selected effect indicator  282  corresponding to the bluish color effect and the effect indicator corresponding to the complementary, cyanish color effect. 
     Also in response to the received drag gesture  242  selecting the effect indicator  282 , the image processing application  200  can change the selected sky blue color to a more bluish sky color that matches the new color indicator  282 - i  shown in  FIGS. 2E-2F . The changed more bluish sky color of the image  205  can be displayed by the image processing application  200 , in real time, while the user performs the drag gesture  242 . The fraction of the change from the selected color (displayed in the reference color indicator  281 ) to the more bluish sky color indicated by the new color indicator  282 - i  is proportional to the length of the upwards drag gesture  242 . 
     Furthermore, as the user drags upward  242  the effect indicator  282 , the image processing application  200  causes the 2-point color control tool to gradually fade out-of-view and removes it completely after effect indicator  282  has been dragged by a predetermined vertical distance from the specified point  220 , e.g., when the changed more bluish sky color matches the new color indicator  282 - i  associated with the 4-point color control tool  280  depicted in  FIGS. 2E-2F . 
     After applying the bluish color effect corresponding to the effect indicator  282  selected by the user with the drag gesture  242 , the image processing application  200  can receive another request  240  from the user (e.g., via a double-tap gesture) to superimpose the 4-point color control tool  280  at the image location  220 , as illustrated in  FIG. 2E . At that time, the user can drag  244  the effect indicator  284  rightward in the GUI of the image processing application  200 , as shown in  FIG. 2H . In response to the received drag gesture  244  selecting the effect indicator  284 , the image processing application  200  can remove from the 4-point color control tool  280  (superimposed on the image  205  in  FIG. 2E ) the effect indicators corresponding to the bluish and cyanish color effects. In this manner, the 4-point color control tool  280  can convert into a 2-point color control tool that retains only the selected effect indicator  284  corresponding to the more saturated color effect and the effect indicator corresponding to the complementary, less saturated color effect. 
     Also in response to the received drag gesture  244  selecting the effect indicator  284 , the image processing application  200  can change the selected sky blue color to a more saturated sky blue color that matches the new color indicator  284 - i  shown in  FIGS. 2E-2F . The changed more saturated sky blue color of the image  205  can be displayed by the image processing application  200 , in real time, while the user performs the drag gesture  244 . The fraction of the change from the selected color (displayed in the reference color indicator  281 ) to the more saturated sky blue color indicated by the new color indicator  284 - i  is proportional to the length of the rightward drag gesture  244 . 
     Furthermore, as the user drags rightward  244  the effect indicator  284 , the image processing application  200  causes the 2-point color control tool to gradually fade out-of-view and removes it completely after effect indicator  284  has been dragged by a predetermined horizontal distance from the specified point  220 , e.g., when the changed, more saturated sky blue color matches the new color indicator  284 - i  associated with the 4-point color control tool  280  depicted in  FIGS. 2E-2F . 
     In  FIG. 2I , the image processing application  200  can superimpose another instance of the 4-point color control tool  270  (from here on referred to as the 4-point color control tool  270 ′) on the digital image  205 , in response to the tan color selection  230 , specified by the user at the image point  220 ′, e.g., via a single-tap gesture. The 4-point color control tool  270 ′, and its effect indicators are described above in connection with  FIG. 2B . In  FIG. 2J , the user can drag  238  the effect indicator  278 ′ leftward in the GUI of the image processing application  200 . In response to the received drag gesture  238  selecting the effect indicator  278 ′, the image processing application  200  can remove from the 4-point color control tool  270 ′ (superimposed on the image  205  in  FIG. 2I ) the effect indicators corresponding to the deeper and paler color effects. In this manner, the 4-point color control tool  270 ′ can convert into a 2-point color control tool that retains only the selected effect indicator  278 ′ corresponding to the lighter color effect and the effect indicator corresponding to the complementary, darker color effect. 
     Also in response to the received drag gesture  238  selecting the effect indicator  278 ′, the image processing application  200  can change the selected tan color to a lighter tan color that matches an associated new color indicator shown in  FIG. 2I . The changed, lighter tan color of the image  205  can be displayed by the image processing application  200 , in real time, while the user performs the drag gesture  238 . The fraction of the change from the selected color (displayed in the reference color indicator shown at the center of the 4 point color control tool  270 ′ in  FIG. 2I ) to the lighter tan color indicated by the associated new color indicator is proportional to the length of the leftward drag gesture  238 . 
     Furthermore, as the user drags leftward  238  the effect indicator  278 ′, the image processing application  200  causes the 2-point color control tool to gradually fade out-of-view and removes it completely after effect indicator  278 ′ has been dragged by a predetermined horizontal distance from the specified point  220 ′, e.g., when the changed, lighter tan color matches the associated new color indicator depicted in  FIG. 2I . 
     Upon receiving from the user the drag gesture  238  selecting the lighter color effect associated with the effect indicator  278 ′, and prior to changing the selected tan color in accordance with the selected lighter color effect, the image processing application  200  can store the RGB values  218  corresponding to the selected tan color at the specified image location  220 ′. In some implementations, the stored RGB values  218  corresponding to the selected tan color at the specified image location  220 ′ can be displayed in the GUI associated with the image processing application  200 , along with the stored RGB values  216  corresponding to the selected sky blue color at the specified image location  220 . By storing the RGB values  216  and  218 , corresponding to the selected colors at respective specified image locations  220  and  220 ′, prior to applying the respective selected color effects or preset adjustments, the image processing application  200  can undo either one of the respective color changes. For example, to undo a color effect or preset adjustment applied to one of the two selected color, the user can first select the displayed RGB values associated with the one of the two selected colors, and then can unselect the control  214  displayed on the GUI associated with the image processing application  200 . 
     In this fashion, the technologies described in connection with systems  100  and  200  provide a simple and intuitive color adjustment mechanism operable by a user who is unfamiliar with hue, luminance, saturation, brightness, and other color transformations. The foregoing concepts are known in color science but are unknown to most users. In addition, the disclosed technologies can be executed on mobile devices for which, typically, display real estate come for a premium. 
       FIG. 3  shows an example of a method for applying color effects and preset adjustments or both to a digital image within an on-screen image adjustment environment. In some implementations, the method  300  can be executed by one or more computing appliances, for example by the mobile device  102  in conjunction with system  100  (or  200 ), to perform color adjustments of a digital image. For instance, the process  300  can be applied to a digital image displayed in a predetermined region of a user interface of an image processing application by using a color control tool overlaid on the digital image. 
     At  310 , a digital image including of a plurality of colors is presented within a graphical user interface (GUI) on a display device. In some implementations, the image processing application, with which the GUI is associated, can detect one or more colors of the digital image for which color effects and preset adjustments are available. In such implementations, the image processing application can mark on the digital image the detected one or more colors to indicate to the user that the marked one or more colors can be changed. 
     At  320 , user input selecting a color within the digital image is received. In some implementations, the user can select the color based on self-assessment. In other implementations, the user can select the color from among the one or more colors marked by the image processing application, as described above at  310 . The color selection can be provided by the user via touch gestures (e.g., single-tap, double-tab, etc.), or via a mouse/keyboard input. 
     At  330 , a color control tool is displayed within a graphical user interface (GUI) and superimposed on the digital image being manipulated. The color control tool is configured to cause change of a selected color within the digital image in accordance with user input specifying movement within the GUI. Further, the color control tool includes a plurality of new color indicators each indicating a new color to which the selected color will change in response to an associated predetermined movement within the GUI. For each one of the plurality of new color indicators, a new color indicated by a new color indicator is obtained from the selected color by applying an associated color effect or a preset adjustment of a plurality of color effects and preset adjustments corresponding to the plurality of respective new color indicators. Each one of the plurality of color effects or preset adjustments can include two or more color transformations that are combined in an associated predefined proportion. For example, the two or more color transformations combined in the associated predefined proportion include either of gamma, luminance, saturation, contrast, or brightness adjustments. Moreover, the associated predetermined movement within the GUI, responsible for changing the selected color to the new color, corresponds to application of an associated effect to the selected color. 
     In some implementations, the displayed color indicator tool is superimposed on a portion of the image that includes the selected color. In some implementations, the image processing application can access, from among a plurality of effects stored on storage, multiple color effects and preset adjustments applicable to the selected color. As such, the color control tool can be populated, by the image processing application, with respective multiple new color indicators corresponding to the accessed multiple color effects and preset adjustments applicable to the selected color. Moreover, all the multiple new color indicators that populate the color control tool can be displayed in the GUI associated with the image processing application. Alternatively, the image processing application can concurrently display in the GUI only a predefined quantity of the multiple new color indicators that populate the color control tool. In some implementations, the image processing application can retrieve, from among the plurality of color effects and preset adjustments stored on the storage, only a predefined quantity of the color effects and preset adjustments, applicable to the selected color, equal to the predefined quantity of new color indicators associated with the color control tool to be displayed in the GUI. 
     At  340 , user input specifying a direction of movement within the GUI relative to the plurality of new color indicators is received via the color control tool. In some implementations, the plurality of new color indicators can be distributed radially around a reference location. The specified direction of the associated predetermined movement with respect to the reference location represents selection of an effect to be applied to the selected color. Additionally, a length of the associated predetermined movement represents a magnitude of the effect selected to be applied to the selected color. The user can specify the direction and the length of the associated predetermined movement by using a drag gesture input via a touch-sensitive display or a mouse/keyboard. 
     At  350 , the selected color is changed to match the new color indicator associated with the specified direction of movement. In some implementations, the digital image display can be updated in real time to show a result of changing the selected color to match the new color indicator associated with the received user input via the color control tool. The received user input selecting the color within the digital image can indicate an image pixel having the selected color. In some implementations, the selected color is changed only within a contiguous portion of the image that includes the indicated pixel. In other implementations, the selected color is changed throughout the image, for example, within all contiguous portions of the image that include pixels having the selected color. 
       FIG. 4  is a block diagram of an example of a mobile device  400  operated according to the technologies described above in connection with  FIGS. 1-3 . For example, a mobile device that can be configured to perform the technologies disclosed in this specification is the smart phone  102  described above in connection with  FIG. 1 . The mobile device  400  can include memory interface  402 , one or more data processors, image processors and/or processors  404 , and peripherals interface  406 . Memory interface  402 , one or more processors  404  and/or peripherals interface  406  can be separate components or can be integrated in one or more integrated circuits. Processors  404  can include one or more application processors (APs) and one or more baseband processors (BPs). The application processors and baseband processors can be integrated in one single process chip. The various components in mobile device  400 , for example, can be coupled by one or more communication buses or signal lines. 
     Sensors, devices, and subsystems can be coupled to peripherals interface  406  to facilitate multiple functionalities. For example, motion sensor  410 , light sensor  412 , and proximity sensor  414  can be coupled to peripherals interface  406  to facilitate orientation, lighting, and proximity functions of the mobile device. Location processor  415  (e.g., GPS receiver) can be connected to peripherals interface  406  to provide geopositioning. Electronic magnetometer  416  (e.g., an integrated circuit chip) can also be connected to peripherals interface  406  to provide data that can be used to determine the direction of magnetic North. Thus, electronic magnetometer  416  can be used as an electronic compass. Accelerometer  417  can also be connected to peripherals interface  406  to provide data that can be used to determine change of speed and direction of movement of the mobile device. 
     Camera subsystem  420  and an optical sensor  422 , e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as recording photographs and video clips. 
     Communication functions can be facilitated through one or more wireless communication subsystems  424 , which can include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem  424  can depend on the communication network(s) over which a mobile device is intended to operate. For example, a mobile device can include communication subsystems  424  designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi or WiMax network, and a Bluetooth network. In particular, the wireless communication subsystems  424  can include hosting protocols such that the mobile device can be configured as a base station for other wireless devices. 
     Audio subsystem  426  can be coupled to a speaker  428  and a microphone  430  to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording, and telephony functions. 
     I/O subsystem  440  can include touch surface controller  442  and/or other input controller(s)  444 . Touch-surface controller  442  can be coupled to a touch surface  446  (e.g., a touch screen or touch pad). Touch surface  446  and touch surface controller  442  can, for example, detect contact and movement or break thereof using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with touch surface  446 . 
     Other input controller(s)  444  can be coupled to other input/control devices  448 , such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of speaker  428  and/or microphone  430 . 
     In some implementation, a pressing of the button for a first duration may disengage a lock of the touch surface  446 ; and a pressing of the button for a second duration that is longer than the first duration may turn power to mobile device  400  on or off. The user may be able to customize a functionality of one or more of the buttons. The touch surface  446  can, for example, also be used to implement virtual or soft buttons and/or a keyboard, such as a soft keyboard on a touch-sensitive display. 
     In some implementations, mobile device  400  can present recorded audio and/or video files, such as MP3, AAC, and MPEG files. In some implementations, mobile device  400  can include the functionality of an MP3 player, such as an iPod™. Mobile device  400  may, therefore, include a pin connector that is compatible with the iPod. Other input/output and control devices can also be used. 
     Memory interface  402  can be coupled to memory  450 . Memory  450  can include high-speed random access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, and/or flash memory (e.g., NAND, NOR). Memory  450  can store operating system  452 , such as Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. Operating system  452  may include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, operating system  452  can include a kernel (e.g., UNIX kernel). 
     Memory  450  may also store communication instructions  454  to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers. Memory  450  may include graphical user interface instructions  456  to facilitate graphic user interface processing; sensor processing instructions  458  to facilitate sensor-related processing and functions; phone instructions  460  to facilitate phone-related processes and functions; electronic messaging instructions  462  to facilitate electronic-messaging related processes and functions; web browsing instructions  464  to facilitate web browsing-related processes and functions; media processing instructions  466  to facilitate media processing-related processes and functions; GPS/Navigation instructions  468  to facilitate Global Navigation Satellite System (GNSS) (e.g., GPS) and navigation-related processes and instructions; camera instructions  470  to facilitate camera-related processes and functions; magnetometer data  472  and calibration instructions  474  to facilitate magnetometer calibration. The memory  450  may also store other software instructions (not shown), such as security instructions, web video instructions to facilitate web video-related processes and functions, and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions  466  are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively. An activation record and International Mobile Equipment Identity (IMEI) or similar hardware identifier can also be stored in memory  450 . Memory  450  can include integrated color adjustment instructions  476  that can include preset adjustments, generic and specific effects, and other related functions described with respect to  FIGS. 1-3 . 
     Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. Memory  450  can include additional instructions or fewer instructions. Furthermore, various functions of the mobile device may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits. 
     Implementations of the subject matter and the functional operations described in this specification can be configured in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be configured as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible nonvolatile program carrier for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. The computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them. 
     The term “data processing apparatus” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. 
     A computer program (which may also be referred to or described as a program, software, a software application, a module, a software module, a script, or code) can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     The processes and logic flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
     Computers suitable for the execution of a computer program include, by way of example, can be based on general or special purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a central processing unit for performing or executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a universal serial bus (USB) flash drive), to name just a few. 
     Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
     To provide for interaction with a user, implementations of the subject matter described in this specification can be configured on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In addition, a computer can interact with a user by sending documents to and receiving documents from a device that is used by the user; for example, by sending web pages to a web browser on a user&#39;s client device in response to requests received from the web browser. 
     Implementations of the subject matter described in this specification can be configured in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described in this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet. 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be configured in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be configured in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.