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HDR Alpha

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Mike Blackney

Posts: 375
Filters: 57
Sorry if this has already been discussed smile:)

I've just noticed that alpha channels don't seem to have HDR like the RGB channels. Is this intentional? Actually, maybe that's not it, maybe the eyedropper isn't reading HDR alpha.

I'm trying to use all four channels of a script component for debugging and whenever I send a negative value to A it's clamped at 0.
Posted: August 5, 2010 8:08 am   Details E-Mail
Mike Blackney

Posts: 375
Filters: 57
If it helps, I just checked that it's not the eyedropper but the alpha channel that's clamped. I used a map filter and returned the alpha in the r,g,b HDR channels and they were all zero smile:(
Posted: August 7, 2010 8:50 am   Details E-Mail
saurabhgayali
Saurabh Gayali
Posts: 183
Filters: 84
what could a negative alpha mean smile:D

i really think we cannot have a negative alpha
saurabh.gayali@gmail.com
Posted: February 18, 2011 7:13 am   Details E-Mail
Betis
The Blacksmith

Posts: 1207
Filters: 76
I think the actual effect wouldn't change if it was negative, I think Mike is curious about the data aspect, like storing 4 HDR values in a single pixel, and then you could have more room for math instead of staying in LDR mode.
Roses are #FF0000
Violets are #0000FF
All my base are belong to you.
Posted: February 18, 2011 9:45 pm   Details E-Mail
Sphinx.
Filter Optimizer

Posts: 1750
Filters: 39
I needed that several times too - having four HDR capable channels would make things easier when you're using the channels for special purposes.

The problem is of course when components perform blending and use the alpha channel as it is supposed to be used. Here the 0..1 range is assumed.

I'm guessing that a lot of range checking is going on currently with the alpha channel - perhaps these checks could be reduced to a minimum so that the alpha stays HDR when possible, and only components that essentially need the 0..1 range will clamp the range.
Njyldgarkn init/prepare process x no. of render blocks x no. of passes
Posted: February 22, 2011 2:13 am   Details E-Mail

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