Computer graphics processing and selective visual display system – Computer graphics processing
Reexamination Certificate
1998-08-12
2001-04-03
Vo, Cliff N. (Department: 2772)
Computer graphics processing and selective visual display system
Computer graphics processing
C345S440000
Reexamination Certificate
active
06211881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to graphical images and, more particularly, to format conversion of graphical images.
2. Description of the Related Art
Graphic images are often stored as image files in a variety of different formats. Often these formats contain some sort of compression to keep the size of the image files manageable. For example, GIF, TIFF and JPEG are popular formats for image files.
However, with conversion between image formats sometimes features supported in one format are not supported in the other format. Such discrepancies lead to incomplete conversion of the images such that the resulting images when displayed are not identical and sometimes have distinct differences. For example, GIF89a supports transparency, but JPEG does not. Hence, conversion of GIF89a images presents a problem because JPEG does not support transparency data. For example, straightforward conversion of GIF89a images to JPEG images often results in an undesirable color appearing in the resulting JPEG image. This is due to the use of an unusual color in the GIF89a image as the transparency color. With GIF89a images, the transparency color is never seen because it is treated as “transparent” when displayed. JPEG images, however, have no transparency support, so the conversion to JPEG results in a color (usually an unusual color) undesirably appearing when the JPEG image is viewed.
Thus, there is a need for improved techniques for image format conversion between formats having different transparency support.
SUMMARY OF THE INVENTION
The invention relates to improved image format conversion techniques that provide improved conversion from an image format supporting transparency to an image format not supporting transparency. The invention replaces a transparency color in an original image format prior to format conversion. Consequently, the format conversion uses the replacement transparency color instead of the original transparency color, and thus is able to provide improved image conversion when converting from an image format supporting transparency to an image format not supporting transparency. The replacement transparency color can be any desirable color, but is preferably chosen to blend with the image. The replacement transparency color can also be matched to the background color.
The invention can be implemented in numerous ways, including as a method, an apparatus, a system, or computer readable medium. Several embodiments of the invention are summarized below.
As a method for converting a source image file having a first image format to a target image having a second image format, one embodiment of the invention includes the acts of: determining whether the source image having with the first image format uses at least one transparent portion; receiving a color table from the source image file; identifying a transparent color for the at least one transparent portion from the color table; determining a replacement transparent color for use with the target image having the second image format; modifying the color table by substituting the replacement transparent color for the transparent color; and thereafter converting the source image file having the first image format to the target image file having the second image format in accordance with the modified color table.
As a method for converting a source image file having a first image format to a target image having a second image format, one embodiment of the invention includes the acts of: allocating a memory block in the memory of the computer system; reading a header block from the source image file; reading a logical screen descriptor block from the source image file; determining whether a color table is present in the source image file; reading the color table into the memory block when the determining act determines that the color table is present in the source image file; reading a graphic control block for an image block in the source image file; determining whether transparency is used in the image block by an examination of the graphic control block; identifying a transparent color index for the color table; determining a replacement transparent color for use with the target image having the second image format, where the second image format does not support transparency; modifying the color table by substituting the replacement transparent color for the transparent color; and thereafter converting the source image file having the first image format to the target image file having the second image format in accordance with the modified color table.
As a computer readable medium containing computer program code for converting a source image file having a first image format to a target image having a second image format, an embodiment of the invention includes: computer program code for receiving the source image file having with the first image format that uses at least one transparent portion; computer program code for receiving a color table from the source image file; computer program code for identifying a transparent color for the at least one transparent portion from the color table; computer program code for determining a replacement transparent color for use with the target image having the second image format; computer program code for modifying the color table by substituting the replacement transparent color for the transparent color; and computer program code for converting the source image file having the first image format to the target image file having the second image format in accordance with the modified color table.
The advantages of the invention are numerous. One advantage of the invention is that display of the image resulting from the image format conversion appears more like the original image. Another advantage of the invention is that the transparency color for those portions of an image intended to be transparent is controllable.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
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Gabler Jeffrey R.
Starnes Darrell J.
Akin Gump Strauss Hauer & Feld & LLP
Compaq Computer Corporation
Vo Cliff N.
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