Abstract:
An image processor converts white areas displayable on a video display screen to white areas outlined in black and suitable for printing on white paper. In addition, black areas that are displayed on a video screen are converted to white for printing on white paper.

Description:
BACKGROUND of the INVENTION 
     This invention pertains to an apparatus and method for converting color image data for display on a display screen to color image data for printing on a color printer. This application claims the foreign priority benefits of Japanese Application No. 2-273508 which was filed on Oct. 15, 1990. This Japanese application and its translation are wholly incorporated by reference herein. 
     The background color for a color display screen is usually selected such that it will contrast with the color or colors of the image to be displayed on the screen. When that same image is printed on a color printer, however, the shape of the image may be ill defined if the color of the paper is used as the background, and one of the colors of the image is substantially identical to the color of the paper. This is particularly true if an area at the boundary of the image is substantially identical to the color of the paper. 
     It is well known to print an image and its background exactly as they appear on a display screen, such that a black background on the screen prints out as a black background on the paper. However, if the background is not printed such that the background takes on the same color as the paper, the printed image usually creates a similar, but different impression as the same image displayed on the screen. 
     It is also well known to print white areas on a display screen as black areas on the paper, and to not print a black area on display screen. Thus, when using white paper, the image on the display screen is inverted, such that black prints out as white, and white prints out as black. In this method, however, a white image, such as the white bird of FIG. 13, is printed as a black bird on the paper. Thus, this method results in a printed image that differs substantially from the image that&#39;s displayed on the screen. 
     Accordingly, the invention described below provides a means for converting image data representing a white area on the screen (or other color that&#39;s the same color as the printer paper) into image data for printing an outline of the white area. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the preferred embodiment of an information processing apparatus constructed in accordance with the present invention. 
     FIGS. 2-10 are block diagrams showing memory areas in the RAM of the preferred embodiment of FIG. 1. 
     FIG. 11 is a block diagram showing a buffer for printed output in the RAM of the preferred embodiment of FIG. 1. 
     FIG. 12 illustrates how the image of FIG. 13 appears when it is printed using the apparatus and method of the present invention. 
     FIG. 13 illustrates an image as it appears on a color display screen. 
     FIG. 14 illustrates how the image of FIG. 13 appears on a prior art printing apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an embodiment of an image processing apparatus according to the present information. Referring to this figure, a Video RAM or VRAM 1 stores data corresponding to one complete screen of data on a color display screen. The contents of the VRAM 1 is rewritten by a Microprocessor Unit or MPU 2 and read out by a CRT Controller or CRTC 3 to produce a color image on the color display screen of a color display 4. The MPU 2 functions under a control program 6 and converts data for the color display screen in the VRAM 1 into data for color printing, using various memory areas in the RAM 7. The converted data is outputted, through a serial-to-parallel converter 8, to a color printer 9. 
     A complete screen of color data is stored in a first memory area 11 of the RAM 7. The information stored in this first memory area 11 consists of data that represents the three primary colors; specifically, red, green and blue (R, G and B, respectively). FIG. 2 illustrates a portion of the first memory area 11 in which storage areas for display row &#34;n&#34; and the two adjacent display rows &#34;n-1&#34; and &#34;n+1&#34; are shown. Each storage area for each row includes separate areas for storing the three primary colors for that row. 
     FIG. 3 illustrates the second memory area 12 in which three rows of &#34;white pixel data&#34; are stored. The white pixel data is computed for each pixel of each display row by logically AND&#39;ing the R, G and B bits for that pixel, i.e., logically AND&#39;ing the corresponding R, G and B data that&#39;s stored in the first memory area 11. The result of this logical operation is stored in the corresponding location in the second memory area 12. Thus, if a bit in the second memory area is set to a logical 1, then the pixel that corresponds to that bit is white. 
     FIG. 4 illustrates the third and fourth memory areas 13 and 14, respectively. &#34;White column data&#34; is stored in the third memory area 13, while the inverse of that data is stored in memory area 14. The white column data is computed for each pixel by logically AND&#39;ing the white pixel data (as stored in memory area 12) for a selected pixel with the white pixel data for the pixel immediately above and below the selected pixel. The logical inverse of this white column data is then stored in memory area 14. 
     FIG. 5 illustrates the fifth, sixth and seventh memory areas 15, 16 and 17 respectively. The fifth memory area 15 stores data that is the logical inverse of the data stored in row &#34;n&#34; of the second memory area; that is, the inverse of the white pixel data for row &#34;n&#34;. This inverted white pixel data is then shifted right one bit and stored in the sixth memory area 16. Similarly, the inverted white pixel data is shifted left one pixel and stored in the seventh memory area 17. 
     FIG. 6 illustrates the eighth memory area 18 in which a logical &#34;0&#34; indicates that the corresponding pixel is a white pixel surrounded, on all four side, by four other white pixels. Conversely, a logical &#34;1&#34; indicates that the corresponding pixel is either not white, or one of the surrounding pixels is not a white pixel. This result is obtained by logically OR&#39;ing the corresponding pixels in the fourth, sixth and seventh memory areas. 
     FIG. 7 illustrates the ninth memory area 19 in which the original color data from row &#34;n&#34; of the first memory area is stored. 
     FIG. 8 illustrates the tenth memory area 20 wherein an intermediate color image is stored. This intermediate color is similar to the original color image of the first memory area, except that interior white pixels have been converted to black. This result is accomplished by logically AND&#39;ing each primary color of each pixel of the ninth memory area (which contains a portion of the original color image) with the corresponding pixel of the eighth memory area (wherein a &#34;0&#34; bit indicates that the corresponding pixel is an interior white pixel). 
     FIG. 9 illustrates the eleventh memory area 21 which includes four sub-areas. In the first sub-area, a logical &#34;1&#34; indicates that the corresponding pixel is a &#34;white outline pixel.&#34; A white outline pixel is a white pixel that is not surrounded by four other white pixels, i.e., a white pixel that is not an interior white pixel. This result is achieved by AND&#39;ing each of the three primary colors for each pixel of the tenth memory area. Since the tenth memory area contains the color image in which interior white pixels have been converted to black, the only remaining white pixels must be white outline pixels. 
     In the second sub-area, a logical &#34;0&#34; indicates that the corresponding pixel is either an original interior white pixel (which has been converted to a black pixel in the tenth memory area) or an original black pixel. This result is obtained by logically OR&#39;ing the three primary colors in the tenth memory area. This result in then inverted and stored in the third sub-area such that a logical &#34;1&#34; in the third sub-area indicates that the corresponding pixel is either an original white interior pixel or an original black pixel. 
     To obtain the data for the fourth sub-area of the eleventh memory area, the first and third sub-areas are logically OR&#39;ed. Thus, a logical &#34;1&#34; in this fourth sub-area indicates that the corresponding pixel is either an original white pixel (either interior or outline) or an original black pixel. 
     FIG. 10 illustrates the twelfth memory area in which the final color image is stored. This final color image is obtained by exclusive OR&#39;ing (XOR) each pixel of the intermediate color image as stored in the tenth memory area, with the corresponding pixel of the fourth sub-area of the eleventh memory area. Thus, if a logical &#34;0&#34; is encounterd in the fourth sub-area, indicating that the corresponding pixel is neither black nor white, the primary color data of the original color image is simply copied into the corresponding location of the twelfth memory area. Conversely, if a logical &#34;1&#34; is encountered in the fourth sub-area, indicating that the corresponding pixel is either originally white or black, the corresponding primary colors in the intermediate color image are inverted. This inversion causes original white interior pixels (which are black in the intermediate color image) to be inverted a second time and return to their original white color. Conversely, this inversion causes original white outline pixels (which were not changed in the intermediate color image) to be inverted to black. Consequently, white interior pixels remain white, while white outline pixels are converted to black. In addition, original black areas (which were not changed in the intermediate color image of the tenth memory area) are inverted to white. The final color image, as stored in the twelfth memory area, is then transferred to a buffer 23 and then on to converter 8 and printer 9. FIG. 12 shows the result of a print-out of the display screen image of FIG. 13, while FIG. 14 shows a prior art print-out in which white areas are simply converted to black.