Abstract:
A method for displaying a digital color image to a visually impaired person, includes the steps of: measuring the visual response of the person and specifying a set of enhancement profiles relating to the person&#39;s color and spatial frequency visual perception, adjusting the color content of the digital color image in response to a color content enhancement profile; adjusting the spatial frequency content of the image in response to a spatial frequency profile; adjusting the contrast of the image in response to a contrast adjustment profile; and displaying the adjusted digital image to the person.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of display devices and particularly to the methods and apparatus for the improvement of color and spatial discrimination of pictorial images for viewers with vision impairment. 
     BACKGROUND OF THE INVENTION 
     At present, when a person wants to view a photographic print he simply picks it up and looks at it. However, a person with a visual impairment cannot fully participate in the pleasure of photography due to their lack of visual acuity. The visual shortcomings of these people are partially addressed in U.S. Pat. No. 5,267,331 by Siwoff issued Nov. 30, 1993, entitled Digitally Enhanced Imager for the Visually Impaired, wherein a device is described which scans a page of text and creates a high resolution, high contrast image which is displayed upon a high resolution monitor. This enhancement of text eliminates any “gray” transitions between the text and the background thereby improving resolution. However this process is not applied to pictorial images because it does not improve the appearance of the pictorial image for a person with visual impairment. Also, U.S. Pat. No. 5,467,123 issued Nov. 14, 1995 to Zeevi et al., entitled Apparatus &amp; Method for Enhancing Color Images discloses a color image apparatus comprising apparatus for receiving signals representing a color image, image processing apparatus, and display device for displaying the processed signal. The image signal is processed to improve the appearance of the image for viewers who are color blind. The image processing extracts information that cannot be detected by the user (ex. yellow-blue signals) and adds the extracted information to a channel the user can detect (ex. red-green) thus enhancing their visual discrimination. This approach renders an image that appears extremely unnatural to any viewer, including a viewer that is color blind. There is a need, therefore, for an improved method and apparatus for displaying pictorial images to individuals who have impaired color and/or spatial discrimination. 
     SUMMARY OF THE INVENTION 
     The present invention meets the need by providing a method for displaying a digital color image to a visually impaired person that includes the steps of: measuring the visual response of the person and specifying a set of enhancement profiles relating to the person&#39;s color and spatial frequency visual perception, adjusting the color content of the digital color image in response to a color content enhancement profile; adjusting the spatial frequency content of the image in response to a spatial frequency profile; adjusting the contrast of the image in response to a contrast adjustment profile; and displaying the adjusted digital image to the person. 
     This method and display apparatus, which will be explained in full detail below, enables a visually impaired person to take any image, whether digital or hardcopy, enhance that image according to a measured profile, and output that image to either a monitor or a hard copy output device. This method has a distinct cost and logistical advantage. Rather than producing customized output such as photographs for each visually impaired person, the photograph is simply placed into a reader and either viewed or printed out. Additionally, when compared to the image processing disclosed in U.S. Pat. No. 5,467,123, the present invention produces a more natural looking image with enhanced discrimination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing apparatus for practicing the method of the present invention; 
     FIG. 2 is a diagram useful in explaining the image processing algorithm used in the present invention; 
     FIG. 3 is a flowchart showing the steps of adjusting of color content of an image according to the present invention; 
     FIG. 4 is a flowchart showing the steps of adjusting the contrast content of an image according to the present invention; and 
     FIG. 5 is a flowchart showing the steps of adjusting the spatial frequency content according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referencing first to FIG. 1, an image reading device  10  constructed and operative in accordance with the present invention, includes a color signal separation circuit  20  whose function is to separate the color channels from an image source  30  so that individual components are ready for the next step of image adjustment. These signals are separated into a luminance and two chrominance described as Red/Green, Blue/Yellow, and Black/White, and are indicated in the figure as R/G, B/Y, and BL/W. 
     An enhancement module  40  includes a color content section  50 , a contrast content adjustment section  60 , and a spatial content adjustment section  70 . These adjustments within enhancement module  40  of color section  50 , contrast section  60 , and spatial content section  70  occur sequentially but the order and number of adjustments can be different based on the application. 
     After the adjustments have been made to the signals, they are sent to control and recombination circuitry  80  where they are recombined into an R, G, B signal, which are in turn output to a display screen  90  or a hard copy printer  100 . The display screen  90  can be for example a television receiver, a computer monitor, a personal digital assistant, an electronic picture frame, a data display, or a control panel. The apparatus detailed in FIG. 1 could be implemented either by a software programmed personal computer or by a hardware programmed ASIC device such as those produced by Texas Instruments Corporation, Dallas Tex., wherein specific needs at the time of production would determine specific device part numbers. 
     A measured subject profile  110  is determined by measuring the visual responses and preferences of the user. This measured subject profile  110  is employed to selectively modify the gain or attenuation in sections  50 ,  60  and  70 , thus rendering a pictorial image with more useable information for a person who has impaired color and/or spatial discrimination. The measurement of a users visual response is accomplished by displaying first a series of color patterns to the user, and based upon the user&#39;s responses, a color discrimination characteristic of the user is derived. Secondly, a series of sinusoidal grayscale gratings are displayed to the user and based upon the responses, a luminance discrimination characteristic is measured. Lastly, the preference measurement is accomplished by displaying a series of images with different color saturation, color balance, and tone scale curves. The user will then be asked to indicate which images he/she prefers. The format of the subject profile consists of a series of numbers representing the aforementioned user preferences associated with a particular scene content. These numerical values represent the gain factors for color content adjustment section  50 , contrast adjustment section  60 , and spatial content adjustment section  70  which are detailed in FIG.  1 . 
     Referring now to FIG. 2, the enhancement algorithms that are used in the present invention will be described in more detail. The digital image  115  is comprised of digital image content  120  and represented by equation  125  which is written as I (c) A x1 +B x2 +C x3 +G x4 . I (c)  is the representation of the image components where A x1  represents the color content of the image, B x2  represents the spatial content of the image, C x3  represents the mid-tone contrast of the image, and G x4  represents other relevant content characteristics of the image such as tone scale. 
     The digital image  115  is fed to decomposition algorithm  130  which in turn separates the digital image  115  into it&#39;s constituent attributes  140 ,  150 ,  160 , and  170 . Attribute  140  represents the color content of the image, attribute  150  represents the spatial content of the image (for example, the spatial content of the image can be represented as a spatial frequency profile specified by a plurality of spatial frequency band pass filters), attribute  160  represents the mid-tone contrast content of the image, and attribute  170  represents other relevant content characteristics of the image such as tone scale. 
     Depending on the individual steps of the adjustments, the decomposition of the image will use different algorithms, stored in decomposition algorithm database  135 , and occurs sequentially within decomposition algorithm box  130 . This step is repeated for each individual attribute. 
     For each individual attribute, these components are modified by enhancement algorithm  180  that changes the characteristics of attributes  140 ,  150 ,  160 , and  170  according to the subject profile  110 . For example, the characteristic of the color content is saturation and this value is attenuated or amplified. Similar operations will occur for the other attributes. Once the enhancement algorithm  180  is applied, the enhanced attributes  190 ,  200 ,  210 , and  220  are recombined by adding them together in recombination algorithm  230  that produces the enhanced digital image I (c) ′  240  which is represented as follows: 
     
       
           I   (c)   ′=A   x1   ′+B   x2   ′+C   x3   ′+G   x4 ′ 
       
     
     FIG. 3 further describes the decomposition of color content in the digital image  120 . The digital image  120  is decomposed into its respective color components of Red/Green  250 , Blue/Yellow  260 , and luminance  270  signals. The decomposition algorithm  280  includes components  250 ,  260 , and  270 . Decomposition algorithm  280  is one step in the decomposition algorithm  130 , as shown in FIG. 2, which complements color signal separation circuit  20  as shown in FIG.  1 . 
     Modification algorithm  290  modifies color components  250  and  260  according to the measured subject profile  110 . Mathematical operations within modification algorithm  290  are either amplification or attenuation of color signals Red/Green  250  and Blue/Yellow  260  according to the parameters defined in the measured subject profile  110 . The profile  110  is determined by comparing the subject&#39;s response to that of an average normal observer and the difference between these two responses determines the gains for the enhancement algorithm  180 . The resulting output of modification algorithm  290  is enhanced Red/Green′  255 , Blue/Yellow′  265  and unmodified luminance  270 . 
     Referring now to FIG. 4, the contrast is adjusted using algorithm  300  according to the contrast parameters defined in measured subject profile  110 . Unmodified luminance  270  is adjusted with contrast modification algorithm  300 . The luminance value in profile  110  is determined by comparing the subject&#39;s response to that of an average normal observer and the difference between these two responses determines the gain for the enhancement algorithm  180 . This value could also be determined by the user&#39;s preference. Once the modifications are complete, the color contents  255  and  265  along with modified luminance content  275  is recombined using algorithm  310  and sent to the spatial frequency adjustment step illustrated in FIG.  5 . 
     Decomposing the spatial content of the digital image  120  occurs in step  320  by using either a standard fast Fourier transform function or a standard discrete cosine transform. Both these functions are well known to those skilled in the art. The measured subject profile  110  includes a spatial content parameter that is determined by measuring the contrast sensitivity function of the subject. The contrast sensitivity function of the subject is measured by the sinusoidal grayscale grating method described previously. The spatial content attributes are modified in step  330  based on the measured subject profile  110 . The spatial content value in profile  110  is determined by comparing the subject&#39;s response to that of an average normal observer and the difference between these two responses determines the gain for the enhancement algorithm  180 . The modified signal is then sent to  340  for recombination and the adjusted image  350  is displayed. It should be noted that recombination signals step  310 , shown in FIG. 4, recombination algorithm  230  shown in FIG. 2, and recombination circuitry  80  shown in FIG. 1 are the same step. FIG. 1 is a hardware step; FIG. 2 could be either a software or hardware step; FIG. 4 could be either a software or hardware step. 
     In addition, the subject&#39;s visual response for different subject matter can be measured, and the digital image adjusted according to the subject matter contained in the digital image. For example, the individuals response to scenes containing human faces and scenes not containing human faces can be measured, and when there is a difference in response, the scenes can be modified accordingly. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       10  image reading device 
       20  color signal separation circuit 
       30  image source 
       40  enhancement module 
       50  color section 
       60  contrast section 
       70  content section 
       80  recombination circuitry 
       90  display screen 
       100  hard copy printer 
       110  measured subject profile 
       115  digital image 
       120  image content 
       125  equation 
       130  decomposition algorithm 
       135  database 
       140  color content attribute 
       150  spatial content attribute 
       160  mid-tone contrast attribute 
       170  other relevant characteristic attribute 
       180  enhancement algorithm 
       190  enhanced color content attribute 
       200  enhanced spatial content attribute 
       210  enhanced mid-tone contrast attribute 
       220  enhanced other relevant characteristic attribute 
       230  recombination algorithm 
       240  enhanced digital image 
       250  Red/Green color component 
       255  enhanced Red/Green 
       260  Blue/Yellow color component 
       265  enhanced Blue/Yellow 
       270  luminance signal 
       275  modified luminance content 
       280  decomposition algorithm 
       290  modification algorithm 
       300  contrast adjustment algorithm 
       310  recombination algorithm 
       320  spatial decomposition step 
       330  modify spatial content step 
       340  sent modified signal step 
       350  adjusted image