For those who just wanna know: cards at the time performed math on brightness values assuming a linear brightness scale when it should be logarithmic.
this post was submitted on 06 Dec 2024
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....ish
The maths was right, except it was all being done on colour values than already had the CRTs response curve baked into them. You may have heard of "gamma correction". Well, this is when you correct an images colour values for the display you'll view it on.
Blending before gamma correction and after gamma correction produce very different results. The cards were doing it after. This story is about doing it before.
Paul Debevec had similar observations around the same time. His work at the time was all about HDRI and that was put into Source a few years later.
Figured someone would do it better than me. Thanks for the correction
Fastest way to get an answer on the internet.
"It's a bit technical," begins Birdwell, "but the simple version is that graphics cards at the time always stored RGB textures and even displayed everything as non linear intensities, meaning that an 8 bit RGB value of 128 encodes a pixel that's about 22% as bright as a value of 255, but the graphics hardware was doing lighting calculations as though everything was linear.
Jesus Christ, I knew this was a problem with image editing software back then, but I never knew, that GPU manufacturers fucked it up as well. How did this happen?
I have a good guess on how this would actually happen:
PM: We need this
Specialist: makes this (doesn't check results)
QC: Looks good (but doesn't actually check)
Some updates later may further break the functionality. And as long as numbers aren't blatantly wrong (think 0s everywhere, for example) and nobody checks thoroughly enough, the issue will remain.
I have unfortunate experience of being a part of such a story, haha. There are ways to counter it. Mainly, their project documentation either wasn't up to par or wasn't used as a reference during creation and tests. Either way, it's negligence.
I imagine in case of GPU design, there should be a bunch of tests for image correctness at some point, which would require pixel perfect reproduction to pass.
But it's plausible that tests were running incorrect math too.
"They are just human after aaaall 🎶"
Laziness
Linear is probably a lot faster?
When the HL2 documentary came out, someone said "all these gaming news sites will have contant for months" and they were absolutely right
I do this to my silicon vendor. I apparently made some people's lives very uncomfortable for a good while this past year after I decompiled some of their binary blobs.
That moment when there's one company with which you'd almost be OK if they turned into a monopoly (still no, though).
Valve is that perfect example of being just shitty enough to be annoying without stepping over the line into complete enshittification. But this too will happen. I reckon there'd be good odds of it happening not long after Gabe retires.
That's my main worry, and why I'd never want a monopoly of any sort with contemporary hierarchical structures.
If they ever go public then yes, enshittification is guaranteed. As long as they remain a privately held company, there's a chance they can hold the enshittification at bay.
That explains why Doom 3's shading looked so bad
Wasn't their shading the whole selling point?
Mhm yes, is this going to fuck up older games?
Everyone's saying RGB is the problem, but what's the alternative? CMYK?
The way I read about it they were merely talking about out gamma correction. Or HDR—>SDR mapping - I wouldn’t say the article is super clear.
Allow me to introduce you to the perceptually uniform color spaces, CIELAB, CIELUV and HSLuv, something I needed for a project I was working on a few years ago:
https://programmingdesignsystems.com/color/perceptually-uniform-color-spaces/