Dither 1.9.5 released:
- Bug fixed in Dither_resize16(), displaying green bars when SSE2 optimisations are disabled.
- Better check of stack16 clip dimensions.
Quote:
Originally Posted by Dogway
As a last question, Im forcing to proces Dither_y_gamma_to_linear in PC range to have more data to work with. Do you think this is more detrimental than beneficial?
|
TV range is all about keeping a headroom for the ringing causing by some filters (resizers, sharpeners…), so with PC range this headroom is lost. But this is not a big difference, and the bottom headroom is cleared by the gamma/linear conversion anyway.
Quote:
Originally Posted by Yellow_
the compositing application I'm importing them into assumes linear. So does the Dither_y_gamma_to_linear function serve this purpose?
|
Yes.
Quote:
|
Is it only necessary to linearize the luma, more accurate and technically correct to do it that way before the conversion to RGB, rather than a typical 0.45 reverse gamma on all channels in RGB data after conversion?
|
GammaYUV -> linearYUV -> linearRGB will give you wrong colors. Inverse colorspace conversions should be done in the same gamma/linearity as the forward conversion. For gamma YUV to linear RGB conversion you can use:
Code:
Dither_convert_yuv_to_rgb (output="rgb48y")
Dither_y_gamma_to_linear (tv_range_in=false, tv_range_out=false)
Dither_convey_rgb48_on_yv12 (
\ SelectEvery (3, 0),
\ SelectEvery (3, 1),
\ SelectEvery (3, 2) )
Quote:
|
Also as the source was encoded with a BT709 transfer curve not sRGB 2.2, to undo that ie: linearize YCbCr, I should be assuming something like the reciprocal of 2.35? If I understand correctly this helps prevent compressing shadow detail that can occur applying 0.45 to BT709 source?
|
You're right, it appears that BT709 doesn't use the same transfer curve as sRGB, the slope at 0 in sRGB is much steeper than in BT709. If you want to linearize the R'G'B' components converted from the BT709 Y'CbCr, apply on each one : R = R'/4.5 if R' < 0.081 or R = ((R' + 0.099) / 1.099) ^ (1/0.45) if R' ≥ 0.081. The formula are the same as in sRGB, but with different values. I will add the BT709 mode to Dither conversion functions in a future release.