Hi
I'm trying to paint a region black by modifying that region
coefficients. I am aware of jpegtran and its `-wipe` option and
that's been a big help to understand the internals. However, that
greys out the region and I'm trying to blacken it.
Assuming YCbCr, where with the [-128 127] range black is:
ycbcr([-128 0 0])
I was expecting that zeroing all coefficients of all components and
setting the DC of the first component to:
-CENTERJSAMPLE / comp_info.quant_table[0].quantval[0]
was the way to go but that's not it (I just get a slightly darker
grey).
I can't figure out what should I set the DC coefficients for black.
Can someone help?
Many thanks
David
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