Hi all. Is anyone out there familiar with the IJG API? Here's my
situation. I am working on a filter that requires explicit knowledge of the
DCT coefficients stored in the JPEG file. To get these I am calling
jpeg_read_coefficients(). My problem is that while most of the values are
reasonable (in fact I get an approximation of the image,) several are beyond
what I understand the limit of the DCT algorithm supports. For example, the
dc coefficient for the luminance component of a pure black image has a value
of -1024 when it should be -128. I have tried scaling everything down by a
eight but this results in some fractional values which should not
technically be possible from the 8 bit representation of JPEG files. Is
there some special scaling system? If you don't know the answer to my
specific question, I would still appreciate some suggestions on who I could
contact. I have already searched the documentation that comes with IJG and
have found nothing. Thanks in advance for all your help,
Dave