Abstract:
A method of converting between color spaces where color components are cached when they are well-defined after color space conversion. When the components become undefined after conversion, the cached values are used instead of using an arbitrary default value. The resulting color editing system is “robust” in that it matches users&#39; expectations, shielding them from Surprising glitches introduced by the user of the arbitrary values for undefined color components.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to the field of graphics editing. More particularly, this invention relates to a system and method for converting between color spaces that preserves well-defined color components when converting from a first to a second color space.  
       BACKGROUND OF THE INVENTION  
       [0002]     In graphical applications, colors are specified using controls that reflect the values of color components in various color spaces. Typically, the resulting color is stored in terms of a single canonical color space.  FIG. 1  illustrates three exemplary colors spaces: RGB Cube, HSB Cone and HLS Double-cone. Other color spaces exist and are known by those of ordinary skill in the art, however these are not shown in  FIG. 1 . A color editor control may convert a color between color spaces to allow a user to edit the canonical color in terms of the differing color spaces.  
         [0003]     A side effect of the conversion between color spaces is that individual components may be defined in the original space, but undefined in a target color space, depending on the value of the input color. For example, “black” represented in the RGB color space is (0,0,0). The equivalent color expressed in the HSB color space has a well-defined brightness component but undefined hue and saturation components.  
         [0004]     A simplistic approach to this problem may be to convert from RGB to HSB and fill-in arbitrary default values for the undefined hue and saturation components. However, the user may have already specified values for these components that are expected to be preserved, even if the components are undefined.  FIG. 2  illustrates the problem that results from this simplistic, non-robust approach. In the HSB color space, when the user decreases saturation to zero (see, steps A)-C)), the original hue value is discarded due to an ambiguous conversion. This unexpected behavior is problematic and an inconvenience because as the user moves the saturation level higher (see, steps D) and E)), the hue remains at the arbitrary level assigned by the color editor in step C) (in this case 0). Thus, while only saturation is modified in steps A) and E), hue is changed in step C) and the user is unable to return to the original color in step A).  
         [0005]     Accordingly, there is a need for a system that retains values of color components when they are well-defined after color space conversion. When the components are undefined after conversion, the retained values may be used instead of simply choosing an arbitrary default value. The present invention provides such a solution.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to methods of converting between color spaces where color components are cached when they are well-defined after color space conversion. When the components become undefined after conversion, the cached values are used instead of using an arbitrary default value. The resulting color editing system is “robust” in that it matches users&#39; expectations, shielding them from surprising glitches introduced by the use of arbitrary values for undefined color components.  
         [0007]     Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The foregoing summary, as well as the following detailed description of preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary constructions of the invention; however, the invention is not limited to the specific methods and instrumentalities disclosed. In the drawings:  
         [0009]      FIG. 1  is a diagram of exemplary color spaces;  
         [0010]      FIG. 2  illustrates editing within a color space in accordance with the prior art;  
         [0011]      FIG. 3  is a block diagram showing an exemplary computing environment in which aspects of the invention may be implemented;  
         [0012]      FIG. 4  illustrates the process of converting from the RGB to HSB color spaces in accordance with the present invention;  
         [0013]      FIG. 5  illustrates the process of converting from the HSB to RGB color spaces in accordance with the present invention; and  
         [0014]      FIG. 6  illustrates editing within a color space in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     Exemplary Computing Environment  
         [0016]      FIG. 3  illustrates an example of a suitable computing system environment  100  in which the invention may be implemented. The computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment  100 .  
         [0017]     The invention is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.  
         [0018]     The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network or other data transmission medium. In a distributed computing environment, program modules and other data may be located in both local and remote computer storage media including memory storage devices.  
         [0019]     With reference to  FIG. 3 , an exemplary system for implementing the invention includes a general purpose computing device in the form of a computer  110 . Components of computer  110  may include, but are not limited to, a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . The system bus  121  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, Peripheral Component Interconnect (PCI) bus (also known as Mezzanine bus), Peripheral Component Interconnect Express (PCI-Express), and Systems Management Bus (SMBus).  
         [0020]     Computer  110  typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by computer  110  and includes both volatile and non-volatile media, removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes both volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by computer  110 . Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media.  
         [0021]     The system memory  130  includes computer storage media in the form of volatile and/or non-volatile memory such as ROM  131  and RAM  132 . A basic input/output system  133  (BIOS), containing the basic routines that help to transfer information between elements within computer  110 , such as during start-up, is typically stored in ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit  120 . By way of example, and not limitation,  FIG. 3  illustrates operating system  134 , application programs  135 , other program modules  136 , and program data  137 .  
         [0022]     The computer  110  may also include other removable/non-removable, volatile/non-volatile computer storage media. By way of example only,  FIG. 3  illustrates a hard disk drive  141  that reads from or writes to non-removable, non-volatile magnetic media, a magnetic disk drive  151  that reads from or writes to a removable, non-volatile magnetic disk  152 , and an optical disk drive  155  that reads from or writes to a removable, non-volatile optical disk  156 , such as a CD-ROM or other optical media. Other removable/non-removable, volatile/non-volatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive  141  is typically connected to the system bus  121  through a non-removable memory interface such as interface  140 , and magnetic disk drive  151  and optical disk drive  155  are typically connected to the system bus  121  by a removable memory interface, such as interface  150 .  
         [0023]     The drives and their associated computer storage media, discussed above and illustrated in  FIG. 3 , provide storage of computer readable instructions, data structures, program modules and other data for the computer  110 . In  FIG. 3 , for example, hard disk drive  141  is illustrated as storing operating system  144 , application programs  145 , other program modules  146 , and program data  147 . Note that these components can either be the same as or different from operating system  134 , application programs  135 , other program modules  136 , and program data  137 . Operating system  144 , application programs  145 , other program modules  146 , and program data  147  are given different numbers here to illustrate that, at a minimum, they are different copies. A user may enter commands and information into the computer  110  through input devices such as a keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  120  through a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor  191  or other type of display device is also connected to the system bus  121  via an interface, such as a video interface  190 . In addition to the monitor, computers may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  195 .  
         [0024]     The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 . The remote computer  180  may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  110 , although only a memory storage device  181  has been illustrated in  FIG. 3 . The logical connections depicted include a local area network (LAN)  171  and a wide area network (WAN)  173 , but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet.  
         [0025]     When used in a LAN networking environment, the computer  110  is connected to the LAN  171  through a network interface or adapter  170 . When used in a WAN networking environment, the computer  110  typically includes a modem  172  or other means for establishing communications over the WAN  173 , such as the Internet. The modem  172 , which may be internal or external, may be connected to the system bus  121  via the user input interface  160 , or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer  110 , or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,  FIG. 3  illustrates remote application programs  185  as residing on memory device  181 . It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used.  
         [0026]     Exemplary Embodiments of Robust Interactive Color Editing  
         [0027]     The processes of the present invention are described with reference to  FIGS. 4-6 . Generally, the parameters are:  
         [0028]     1. A canonical color space.  
         [0029]     2. A color space to convert to (i.e., the “display” color space).  
         [0030]     3. A color conversion process.  
         [0031]     4. A caching mechanism.  
         [0032]     Referring now to  FIG. 4 , there is illustrated the process of converting from RGB to HSB, while maintaining well-defined color values. As used herein, “well-defined” means that a particular color is defined unambiguously by a unique color space component triple (i.e., the H, S and B values) in that space. At step  200 , the RGB component values are input. At step  202  it is determined if the RGB values are achromatic. If no, then at step  206 , the hue, brightness and saturation values are calculated according to a well known conversion. Because this is a well-defined color value, the new HSB values are cached at step  208 . At step  218 , the HSB component values are returned to the user.  
         [0033]     If at step  202  the result is yes, then at step  204  it is determined if the color is black (R=G=B=0). If not, then at step  210 , the cached value for hue is used, saturation is set to zero and brightness is calculated. At step  212 , the cached saturation value is updated based on the result of step  210  and the HSB component values are returned at step  218 . If the color is black at step  204 , then the cached hue and saturation values are used and brightness is set to zero at step  214 . The cached values are not updated because of this condition (step  216 ) and the resulting color component values are returned at step  218 .  
         [0034]     Referring now to  FIG. 5 , there is illustrated the process of converting from HSB to RGB, while maintaining well-defined color values. At step  220 , the HSB component values are input. At step  222  it is determined if the saturation value is zero. If yes, then at step  234 , the red, green and blue component values are calculated according to a well known conversion. Because this is a well-defined color value, the new RGB values are cached at step  236 . At step  238 , the RGB component values are returned to the user.  
         [0035]     If at step  222  the result is no, then at step  224  it is determined if the brightness is zero. If yes, then at step  230 , the red, green and blue component values are calculated. At step  232 , the cached hue and saturation values are from the input values at step  220 . The RGB component values are then returned at step  238 . If the brightness is not zero at step  224 , then the red, green and blue component values are calculated at step  226 . However, the cached values are not updated because of this condition (step  224 ) and the resulting RGB color component values are returned at step  238 .  
         [0036]     Thus, the present invention caches a most-recent well-defined value for color components and uses these when:  
         [0037]     1. A color component becomes undefined after being well-defined: use the cached values for the undefined component instead of an arbitrary default value.  
         [0038]     2. A color component becomes well-defined after being undefined: use the cached values for the component when the color conversion moves away from a singularity  
         [0039]     Several caching mechanisms are possible. For example, a vector of approach into singular points in the converted color space may be stored and used to reconstitute the components once the converted color moves away from a singular point. The preferred implementation simply caches component values.  
         [0040]     Referring now to  FIG. 6 , there is the color space conversion of  FIG. 2  showing color editing using the present invention.  FIG. 6  illustrates the improvements of the present invention result from a robust approach. In the HSB color space, when the user decreases saturation to zero (see, steps A)-C)), the original hue value is discarded due to the ambiguous conversion. However, in accordance with the present invention, the well-defined cached value for hue is used. As the user moves the saturation level higher (see, steps D) and E)), the cached hue value is used and, eventually, the user is able to return to the original color in step A).  
         [0041]     Although the present invention has been described in exemplary terms with respect to a conversion between RGB and HSB (and vice versa), other conversions from different color spaces are contemplated by the appended claims.  
         [0042]     While the present invention has been described in connection with the preferred embodiments of the various Figs., it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. For example, one skilled in the art will recognize that the present invention as described in the present application may apply to any computing device or environment, whether wired or wireless, and may be applied to any number of such computing devices connected via a communications network, and interacting across the network. Furthermore, it should be emphasized that a variety of computer platforms, including handheld device operating systems and other application specific operating systems are contemplated, especially as the number of wireless networked devices continues to proliferate. Still further, the present invention may be implemented in or across a plurality of processing chips or devices, and storage may similarly be effected across a plurality of devices. Therefore, the present invention should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the appended claims.