Glow and temp/tint question

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alwes...@gmail.com

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Nov 15, 2021, 1:29:46 PM11/15/21
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Hi everyone,

Two short questions :
1/ I was wondering if there was a way to change temp/tint without affecting the luma.... (and without going on a separate layer with a color only blending mode). Let me know if I am wrong but it seems to me that temp and tint react just like gain adjustment on two different axis.... and so luma seems to be affected by every change....

2/ What is your favorite glow shader effect ? The assimilate Highlight bloom works but if there was a little more complex one in the repository... I'll be happy too.

Thanks in advance,

Best regards,
Alex

alwes...@gmail.com

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Nov 17, 2021, 1:54:22 PM11/17/21
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Hi everyone,

Just bouncing on my own two silly questions :-P
Just found on the manual that regarding temp and tint : " With any adjustment of these parameters SCRATCH attempts to maintain a constant luminance for the image." \o/
Indeed, the different color channel are compensating when adjusting these settings, and yet there is a slight difference in luminosity (mostly when the adjustment is pretty high. It is visible when you make an adjustment on a specific layer and switch this layer from normal to color blending mode : warmer temp goes darker, cooler goes brighter).
Perhaps there is some intrinsic limitation to the accuracy of the compensation ?
Anyway, on that YRGB stuff I was also thinking that a "luma mix" slider could be a great thing even for other RGB adjustments... or is there a tip for that parameter already ?

Cheers,
Alex

Tobias Wiedmer // Cine Chromatix KG

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Nov 17, 2021, 2:28:54 PM11/17/21
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Hi Alex,

for real white balance adjustments you need to do it colourspace aware->gain adjustment in linear (you have to convert properly and you need an inverse tonemapping in case you come from a display referred space)  or offset in log space (best case scenario ACES CC, not ACES cct).

if you want to avoid any luminance shift, you could build a matchbox shader which keeps it constant by comparing lumiance before and after the adjustment. Don’t know if that is very useful, though.

maybe that helps,

cheers,
Tobi
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