Release Notes
Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances
70
Maximum number of colors to use in generating a library-supplied color
map (the actual number of colors is returned in a different field).
Default 256. Ignored when the application supplies its own color map.
boolean two_pass_quantize
If TRUE, an extra pass over the image is made to select a custom color
map for the image. This usually looks a lot better than the one-size-
fits-all colormap that is used otherwise. Default is TRUE. Ignored
when the application supplies its own color map.
J_DITHER_MODE dither_mode
Selects color dithering method. Supported values are:
JDITHER_NONEno dithering: fast, very low quality
JDITHER_ORDEREDordered dither: moderate speed and quality
JDITHER_FSFloyd-Steinberg dither: slow, high quality
Default is JDITHER_FS. (At present, ordered dither is implemented
only in the single-pass, standard-colormap case. If you ask for
ordered dither when two_pass_quantize is TRUE or when you supply
an external color map, you'll get F-S dithering.)
When quantize_colors is TRUE, the target color map is described by the next
two fields. colormap is set to NULL by jpeg_read_header(). The application
can supply a color map by setting colormap non-NULL and setting
actual_number_of_colors to the map size. Otherwise, jpeg_start_decompress()
selects a suitable color map and sets these two fields itself.
[Implementation restriction: at present, an externally supplied colormap is
only accepted for 3-component output color spaces.]
JSAMPARRAY colormap
The color map, represented as a 2-D pixel array of out_color_components
rows and actual_number_of_colors columns. Ignored if not quantizing.
CAUTION: if the JPEG library creates its own colormap, the storage
pointed to by this field is released by jpeg_finish_decompress().
Copy the colormap somewhere else first, if you want to save it.
int actual_number_of_colors
The number of colors in the color map.
Additional decompression parameters that the application may set include:
J_DCT_METHOD dct_method
Selects the algorithm used for the DCT step. Choices are the same
as described above for compression.
boolean do_fancy_upsampling
If TRUE, use direct DCT scaling with DCT size > 8 for upsampling
of chroma components.
If FALSE, use only DCT size <= 8 and simple separate upsampling.