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Blend HDR modes

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Carl
c r v a

Posts: 7163
Filters: 75
It's very hard to make a creative HDR filter when you don't have all the blend modes available, I always seem to stumble and need to use the LDR blend component somewhere in the filter to get the effect I want, destroying the HDR flow ........ can it have all the blend modes? or is this impossible for some reason smile:?:
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Skybase
2D/3D Generalist

Posts: 2850
Filters: 67
I figure the blendmodes available in LDR utilize math that's set within bounds. For example, overlay looks like this: if (Base > ½) R = 1 - (1-2×(Base-½)) × (1-Blend); if (Base <= ½) R = (2×Base) × Blend (source = http://dunnbypaul.net/blends/)

Basically in that given blend there's nothing cumulative as with some other blend modes too. HDR blendmodes like add is just blend+blend meaning that the blendmode can become brighter given no bounds.

Which is why the HDR blendmodes become limited to only several. But put it this way: given the RGB math tools you can try making your own unique blend mode just for the fun of it smile:)
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Carl
c r v a

Posts: 7163
Filters: 75
very interesting Skybase thanks smile8) ....... using the maths tools I don't think I'd be sure if I'm passing on hdr imformation or not. but as you suggest might be fun playing around with them smile:D cheers

ps unfortunatly link didn't work [ page not found ]
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Sphinx.
Filter Optimizer

Posts: 1357
Filters: 38
I can confirm your suspicion: many of the classic blendmodes were designed for 8bpc, i.e. 0..255, a fixed range and a fixed mid point ("gray point"). With HDR you theoretically don't know the min..max range and there is no mid point. Consider the overlay formula Skybase posted above:

Code
if (Base > ½) R = 1 - (1-2×(Base-½)) × (1-Blend);
if (Base <= ½) R = (2×Base) × Blend


Here is what it really says:

Code
min_range = 0
max_range = 1
mid_range = (max_range - min_range) / 2

if (Base > mid_range) R = max_range - (max_range - 2 × (Base - mid_range)) × (max_range - Blend);
if (Base <= mid_range) R = (2×Base) × Blend


But with HDR we don't have predefined min_range and max_range .. see the problem? (this is also the reason as to why invert doesn't make sense with HDR).

What you can do however is to inspect all values in the image and figure out min and max values. You the use these values to "normalize" the image temporarily, run it through LDR blend and convert it back to HDR...

Alternatively you can reduce the contrast greatly, run it through the LDR blend and increase the contrast afterwards..
Njyldgarkn sample cache!
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Skybase
2D/3D Generalist

Posts: 2850
Filters: 67
Oh sweet, more explanation!

http://dunnbypaul.net/blends/ <--- didn't work because there was a ) on the link heh.
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Morgantao
Can't script

Posts: 2185
Filters: 20
Boy I wish my brain wasn't so intollerant to math...
Seems like everything I'm interested in comes to a screeching halt by simple math. Or maybe slams into a math wall would be more like it. smile:(

Just to name a few of my interests that I had to let go due to my nemesis (nemathis): Electronics, Chemestry, Physics, Image processing, Software engineering... smile:cry:
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Carl
c r v a

Posts: 7163
Filters: 75
Thanks for link Skybase, always hope FF would add pinlight as a blend mode you can get some pretty cool blending with it. Sphinx I will try lowering the contrast and see what can happen ........ very helpful from you both thanks smile8)
Morgantao I'm bit like you I have trouble with wrapping my old brain around the more complex maths which is irratating and frustrating smile:( smile:)
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