Release Notes
Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances
68
int h_samp_factor
int v_samp_factor
Horizontal and vertical sampling factors for the component; must
be 1..4 according to the JPEG standard. Note that larger sampling
factors indicate a higher-resolution component; many people find
this behavior quite unintuitive. The default values are 2,2 for
luminance components and 1,1 for chrominance components, except
for grayscale where 1,1 is used.
int quant_tbl_no
Quantization table number for component. The default value is
0 for luminance components and 1 for chrominance components.
int dc_tbl_no
int ac_tbl_no
DC and AC entropy coding table numbers. The default values are
0 for luminance components and 1 for chrominance components.
int component_index
Must equal the component's index in comp_info[]. (Beginning in
release v6, the compressor library will fill this in automatically;
you don't have to.)
Decompression parameter selection
---------------------------------
Decompression parameter selection is somewhat simpler than compression
parameter selection, since all of the JPEG internal parameters are
recorded in the source file and need not be supplied by the application.
(Unless you are working with abbreviated files, in which case see
"Abbreviated datastreams", below.) Decompression parameters control
the postprocessing done on the image to deliver it in a format suitable
for the application's use. Many of the parameters control speed/quality
tradeoffs, in which faster decompression may be obtained at the price of
a poorer-quality image. The defaults select the highest quality (slowest)
processing.
The following fields in the JPEG object are set by jpeg_read_header() and
may be useful to the application in choosing decompression parameters:
JDIMENSION image_widthWidth and height of image
JDIMENSION image_height
int num_componentsNumber of color components
J_COLOR_SPACE jpeg_color_spaceColorspace of image
boolean saw_JFIF_markerTRUE if a JFIF APP0 marker was seen
UINT8 JFIF_major_versionVersion information from JFIF marker