Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances

your own devising). More info about the minimum system library requirements

may be found in jinclude.h.

ADVANCED FEATURES

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Compression parameter selection

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This section describes all the optional parameters you can set for JPEG

compression, as well as the "helper" routines provided to assist in this

task. Proper setting of some parameters requires detailed understanding

of the JPEG standard; if you don't know what a parameter is for, it's best

not to mess with it! See REFERENCES in the README file for pointers to

more info about JPEG.

It's a good idea to call jpeg_set_defaults() first, even if you plan to set

all the parameters; that way your code is more likely to work with future JPEG

libraries that have additional parameters. For the same reason, we recommend

you use a helper routine where one is provided, in preference to twiddling

cinfo fields directly.

The helper routines are:

jpeg_set_defaults (j_compress_ptr cinfo)

This routine sets all JPEG parameters to reasonable defaults, using

only the input image's color space (field in_color_space, which must

already be set in cinfo). Many applications will only need to use

this routine and perhaps jpeg_set_quality().

jpeg_set_colorspace (j_compress_ptr cinfo, J_COLOR_SPACE colorspace)

Sets the JPEG file's colorspace (field jpeg_color_space) as specified,

and sets other color-space-dependent parameters appropriately. See

"Special color spaces", below, before using this. A large number of

parameters, including all per-component parameters, are set by this

routine; if you want to twiddle individual parameters you should call

jpeg_set_colorspace() before rather than after.

jpeg_default_colorspace (j_compress_ptr cinfo)

Selects an appropriate JPEG colorspace based on cinfo->in_color_space,

and calls jpeg_set_colorspace(). This is actually a subroutine of

jpeg_set_defaults(). It's broken out in case you want to change

just the colorspace-dependent JPEG parameters.

jpeg_set_quality (j_compress_ptr cinfo, int quality, boolean force_baseline)

Constructs JPEG quantization tables appropriate for the indicated

quality setting. The quality value is expressed on the 0..100 scale