script2.ijg

DELPHI版的JPEG文件解码源程序

# Here is an example of a successive-approximation script.
# This is equivalent to the default script used by
# "cjpeg -progressive" for YCbCr images:

	# Initial DC scan for Y,Cb,Cr (lowest bit not sent)
	0,1,2: 0-0,   0, 1 ;
	# First AC scan: send first 5 Y AC coefficients, minus 2 lowest bits:
	0:     1-5,   0, 2 ;
	# Send all Cr,Cb AC coefficients, minus lowest bit:
	# (chroma data is usually too small to be worth subdividing further;
	#  but note we send Cr first since eye is least sensitive to Cb)
	2:     1-63,  0, 1 ;
	1:     1-63,  0, 1 ;
	# Send remaining Y AC coefficients, minus 2 lowest bits:
	0:     6-63,  0, 2 ;
	# Send next-to-lowest bit of all Y AC coefficients:
	0:     1-63,  2, 1 ;
	# At this point we've sent all but the lowest bit of all coefficients.
	# Send lowest bit of DC coefficients
	0,1,2: 0-0,   1, 0 ;
	# Send lowest bit of AC coefficients
	2:     1-63,  1, 0 ;
	1:     1-63,  1, 0 ;
	# Y AC lowest bit scan is last; it's usually the largest scan
	0:     1-63,  1, 0 ;

# It may be worth pointing out that this script is tuned for quality
# settings of around 50 to 75.  For lower quality settings, you'd
# probably want to use a script with fewer stages of successive
# approximation (otherwise the initial scans will be really bad).
# For higher quality settings, you might want to use more stages of
# successive approximation (so that the initial scans are not too large).