Display reduction method using sub-pixels

A display reduction of 1/n is performed with a display device, with which three light-emitting elements, which respectively emit light of the three primary colors of R, G, and B, are aligned in a fixed order to comprise one pixel. A plurality of pixels are aligned in a first direction to form one line. A plurality of lines are aligned in a second direction, orthogonal to the first direction, to comprise the display screen. Original image data is converted to working image data by magnifying or reducing the original data by 3/n in the first direction. The working image data are then allocated to the three light-emitting elements that comprise one pixel and the displayed. The display reduction reduces the loss of information compared to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 , an input means 1 inputs information on the operation instructions, etc. A display image storage means 8 (VRAM, etc.) Contains the elements needed for sub-pixel display. A display control means 2 controls the various elements to make display device 3 perform display based on the display image stored in the display image storage means 8 . Display device 3 includes a plurality of sets of three light-emitting elements, which respectively emit light of the three primary colors of R, G, and B. The light-emitting elements are aligned in a fixed order to form one pixel. The pixels are aligned in a first direction to form one line. A plurality of such lines are aligned in a second direction, which is orthogonal to the first direction, to form the display screen. To be more specific, display device 3 may be a color LCD or color plasma display, etc. driven by a driver (not shown) to drive the respective elements of the color LCD or color plasma display, etc. An original image storage means 4 stores the original image data prior to display reduction. The original image data are raster image data or vector image data that are subsequently developed into raster image data. The original image data may be that of a general image or a font. In the process of display reduction by display control means 2 , a working image data storage means 5 stores a temporary working image, obtained by magnification or reduction of the original image stored in original image data storage means 4 . An anti-aliasing process means 6 performs smoothing of the outlines of a given image. A filtering process means 7 performs a filtering process, based on factors to be described below, on the working image data stored in working image data storage means 5 and stores the resulting image storage means 8 . Referring now to FIGS. 3 ( a )-( c ), the factors for a first-stage filtering process are shown for one pixel consisting of the three light-emitting elements (sub-pixels) of R, G, and B. The degrees of contribution to luminance of the subpixels are such that R:G:B&equals;3:6:1. If as shown in FIG. 3 ( a ), the target sub-pixel is an R sub-pixel, since the sub-pixel to its left is a B sub-pixel and the sub-pixel to the right is a G sub-pixel, energy collection is performed so that, for example, a factor of {fraction (1/10)} is allocated from the B sub-pixel to the left (one sub-pixel prior to the target sub-pixel, n-1), {fraction (3/10)} is allocated from the R sub-pixel, which is the target sub-pixel, and {fraction (6/10)} is allocated from the G sub-pixel to the right (one sub-pixel after the target subpixel, n&plus;1. Thus if the respective sub-pixel values V are expressed using a suffix, the value V(n) after the degrees of contribution to luminance are taken into account is such that V(n)&equals;({fraction (1/10)})*V n-1 &plus;({fraction (3/10)})*V n &plus;({fraction (6/10)})*V n&plus;1 . Likewise, the filtering process when the target sub-pixel is a G sub-pixel is as shown in FIG. 3 ( b ). The filtering process when the target sub-pixel is a B sub-pixel is as shown in FIG. 3 ( c ). As is clear from FIGS. 3 ( a )-( c ), if just the factors of the first stage are used, the factors are applied to a total of three sub-pixels centered about the target subpixel. The factors for a second-stage filtering process are described with reference to FIGS. 4 ( a )-( c ). The first stage is exactly the same as that shown in FIGS. 3 ( a )-( c ). Here, when the target sub-pixel is R, since the order of sub-pixels in the stage below the B sub-pixel that branches from the target sub-pixel is GBR as shown in FIG. 4 ( a ), energy collection is performed by allocating factors of {fraction (6/10)}, {fraction (1/10)}, and {fraction (3/10)} in that order from the left side. Likewise, since the order of sub-pixels in the stage below the R sub-pixel that branches from the target sub-pixel is BRG, energy collection is performed by allocating factors of {fraction (1/10)}, {fraction (3/10)}, and {fraction (6/10)} in that order from the left side. Also, for the G sub-pixel that branches from the target sub-pixel, since the order of subpixels in the stage below is RGB, energy collection is performed by allocating factors of {fraction (3/10)}, {fraction (6/10)}, and {fraction (1/10)} in that order from the left side. As a result, the hierarchy shown in FIG. 4 ( a ) is formed. With regard to the R sub-pixel (noted sub-pixel, n) at the center of FIG. 4 ( a ), there are three pathways, passing through the B, R, and G sub-pixels, respectively, of the upper stage that lead to this target sub-pixel. The factor for the value V(n) of the target sub-pixel is ({fraction (1/10)})*({fraction (3/10)})&plus;({fraction (3/10)})*({fraction (3/10)})&plus;({fraction (6/10)})*({fraction (3/10)})&equals;{fraction (30/100)}. The factor for the other sub-pixels for the lowermost stage are determined in the same manner so that the value V(n) after the degrees of contribution to luminance are taken into account is such that V(n)&equals;({fraction (6/100)})*V n-2 &plus;({fraction (4/100)})*V n-1 &plus;({fraction (30/100)})*V n &plus;({fraction (54/100)})*V n&plus;1 &plus;({fraction (6/100)})*V n&plus;2 . Likewise, the filtering process when the target sub-pixel is a G sub-pixel is as shown in FIG. 4 ( b ). The filtering process when the target sub-pixel is a B sub-pixel is as shown in FIG. 4 ( c ). As is clear from FIGS. 4 ( a )-( c ), when factors of two stages are used, the factors are applied to a total of five sub-pixels centered about the target sub-pixel. As examples of modifications of the above, those shown in FIGS. 5 ( a )-( c ) (where equal factors of (&frac13;) are allocated to the second stage) and in FIGS. 6 ( a )( c ) (where equal factors of (&frac13;) are allocated to the first stage) is given. Even when equal allocation is performed on part of the stages as in these examples, if factors that reflect the degrees of contribution to luminance are used in the other stages, this is adequate for practical purposes in many cases. This invention also includes cases where the above weighting is applied to three or more stages. Referring now to the flow chart in FIG. 2 , at step 1 , the display information indicating that display reduction is to be performed is input to input means 1 . The reduction rate (n) is then input from input means 1 (step 2 ). Then in step 3 , display control means 2 takes the original image data from original image data storage means 4 , magnifies or reduces this image by 3/n in the first direction, reduces the original image by 1/n in the second direction, and stores the resulting image in working image data storage means 5 . Either direction (vertical/horizontal) may be selected as the first direction of reduction. Next in step 4 , display control means 2 instructs filtering process means 7 to perform a filtering process, using the factors that reflect the degrees of contribution to luminance, on the working image in working image data storage means 5 . Here, the factors shown in any of FIGS. 3 ( a )-( c ) to 6 ( a )-( c ) may be used. When the filtering process is completed, filtering process means 5 returns the processed image data to display control means 2 . Display control means 2 stores the received data in display image storage means 8 . The storage in display image storage means 8 is not in one pixel units but in units of the three lightemitting elements of R, G, and B that comprise one pixel (that is as a sub-pixel image). Next in step 6 , display control means 2 issues an instruction to antialiasing process means 6 to perform smoothing in the second direction of the subpixel image, stored in display image storage means 8 . Then in step 7 , display control means 2 instructs display device 3 to display the image (in the form of sub-pixel display) by allocating the three-times magnified/reduced pattern to the three light-emitting elements that comprise one pixel of display device 3 based on the display image stored in display image storage means 8 . An example of image reduction by the present embodiment will now be described with reference to FIGS. 7 ( a )-( e ). In this example, image reduction is performed under the same conditions (½ in the vertical and horizontal directions) as those of the prior-art example shown in FIG. 8 . The first direction is the horizontal direction of FIG. 8 and the second direction is the vertical direction of FIG. 8 . First, the original image is that shown in FIG. 7 ( a ). The original image data for this image are stored in original image data storage means 4 . Image control means 2 then reduces this image by ½ in the vertical direction and magnifies this image by {fraction (3/2)} in the horizontal direction as shown in FIG. 7 ( d ) and stores the resulting image in working image data storage means 5 . In achieving the condition of FIG. 7 ( d ) from that of FIG. 7 ( a ), the condition of FIG. 7 ( d ) is reached via the conditions shown in FIGS. 7 ( b ) and 7 ( c ). In any case, since the working image data shown in FIG. 7 ( d ) is stored in working image data storage means 5 , display control means 2 performs allocation of the working image data of FIG. 7 ( d ) in a manner suitable for sub-pixel mapping and stores the image data of FIG. 7 ( e ) in display image storage means 8 . Display reduction, based on a reduced image of sub-pixels, each of which comprises one-third of one pixel, in the first direction (the horizontal direction in this example) is thus performed. It can be understood that even in comparison to the ideal reduced image shown in FIG. 7 ( f ) the image reduction by this embodiment results in the good image reduction result shown in FIG. 7 ( e ), with which the white part of the row at the right is not lost. As has been described above, by this invention, the loss of information is limited during display reduction and a reduced display that is easy to view is realized. Also, the filtering factors are arranged to perform high quality display with minimum color irregularities. Although the invention is described above as controlling R, G and B (red, green and blue) emitters, in some situations, other colors may be selected to produce the desired visual impression. Therefore, the invention should be seen by one skilled in the art to include any combination of color emitters. For example, there may be applications in which only two emitters are required to form a pixel. In other cases, more than three color emitters. For purposes of description, however, the above specification recites the common primary colors of R, G and B colors. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.