Entry
R0 = pointer to buffer for JPEG data
R1 = size of JPEG data buffer
R2 = pointer to block of parameters
+0 width of image in pixels
+4 height of image in pixels
+8 quality value (0 - 100): lower quality results in smaller image
+12 number if 8 bit components in source: 3 => 24 bit colour, 1 => 8 bit greyscale
+16 horizontal DPI of image, or 0 if unknown
+20 vertical DPI of image, or 0 if unknown
R3 = pointer to workspace area, or 0 for the CompressJPEG module to allocate its own workspace from the RMA
R4 = size of workspace area (if R3 /= 0)
Exit
R0 = JPEG tag, to be passed to other CompressJPEG SWIs
This call starts the JPEG compression process, setting up various parameters for it.
The buffer for the JPEG data should be as large as possible, since the JPEG compression routines cannot guarantee to compress the image by a fixed amount.
If you wish to supply your own workspace area, its required size for a colour (24 bit) image is:
20000 + ((image width rounded up to a multiple of 16) × 30)
and its required size for a greyscale (8 bit) image is:
20000 + ((image width rounded up to a multiple of 16) × 9)
An error is returned if the workspace area becomes full.
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