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Captain Disillusion – The Horrors of the Alpha Channel
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View Reddit by BonkerHonkers – View Source
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Captain Disillusion – The Horrors of the Alpha Channel
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View Reddit by BonkerHonkers – View Source
Ohhhhh that’s cool. I don’t get it. 😂
But I love his videos and watched anyway.
“Train a generative adversarial net on some timelapse footage of people photoshopping memes”
I feel so attacked.
why is he silver
This one was way too technical for me to follow closely, but at least I got the gist of what he meant, even if I still don’t fully understand how software handles the ful process. A cool view of why you get artifacts like that on pictures though.
Use Nuke. Unlike after effects it makes premult and unpremult operations easy and clear
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I love this channel so much. His BTTF videos and the Flight of the Navigator one are a lot of fun and not too technical if anyone’s looking for a good starting point.
WITNESS ME
That ending lmao
As a stable diffusion guy that last joke was very rutkowski
My meme compositing efforts suddenly make much more sense and somehow less at the same time.
Holy shit he’s making videos again! This is a great day for the internet.
You can get Bloom in the alpha?? How?
This guy is the Bill Nye of VFX.
I often have no clue what he’s talking about, but I love watching him talk about it.
I am a graphic designer and I often output prores files with alpha in after effects. Choosing between “pre-multiplied” or “straight” is always a struggle when handing off to different editors. I just default to straight now.
In the opening when he shows the old way of doing it, why are they cutting a black super-hero shaped hole out of the sky? Wouldn’t that just be the background, beneath everything, and the rest goes on top?
While we’re here on alpha channels… can anyone explain to me:
Why so often, sometimes the majority of image results when searching for an image with transparency. Results contain the telltale white and grey checkerboard of an alpha channel… but its a ruse and the checkerboard is opaque and burned into the image. What gives and why is this a such a common thing?
Educational! 🤣
I feel like this video should have just been an email to Adobe support, maybe a forum post.
Man discovered the best way to pronounce GIF and I am absolutely down for it.
Jife for life.
I love how at the end he attempts to finish with a positive closing message, giving wise advice given all the problems he has just explained, just to go back to CD’s cynical and sarcastic tone right away, ranting about AI. Lmao.
Any chance someone can explain why premultiplication is worth doing? I couldn’t quite get that from the video
Can someone explain who this guy is and why his videos are apparently interesting to many people? He always covers topics which are really obscure, but acts like everyone should know about them. Where did this guy come from and why is he acting like he’s some sort of factor?
Wild. I knew [this post was wrong](https://old.reddit.com/r/halo/comments/yaosff/when_youve_been_waiting_your_whole_life_to_meet/), but didn’t know why. But the ‘ghost’ part of the video explains it. 🙂
I don’t usually work with images, but last month I had to find out how alpha blending and gamma correction works. This video would have come in handy if he had released it just a bit earlier…
The Captain’s videos are always so damn informative while remaining interesting to watch. He’s a good teacher.
I was just browsing some older Captain D videos this past week thinking it’s been a while since we’ve had an upload and here one is. I guess he’s mastered the timing of the upload schedule to coincide with when people start getting withdrawal.
One of the most underrated guys on YouTube.
i dont understand anything and yet im entertained.
I understood the Hans and Franz reference!
I didn’t understand any of the rest of it.
I miss when he posted more regularly. It seems like we get a 6 min video every 6 months now.
I wish someone would give him
Money for a full Netflix style series. He’s so good
I’m a graphics/gpu engineer and I don’t think I could really get the point from this video alone. Pre-multiplied alpha is a super tricky subject with lots of really weird historical quirks.
For people who want another expl:
Not multiplied alpha gives you a color and a transparency per pixel. This means you can have a pixel that is bright pink, but completely transparent (meaning it doesn’t show up at all, but the color property is still stored intact) this means you can freely edit color and transparency separately. This is how you usually “work” in photoshop etc. One weird issue with this is that if you have a fully transparent pixel, the color doesn’t matter, and often the color is kinda undefined (what is the “color” of something that isn’t there), so often it’s just picked black or white, or in more advanced situations (video games textures) you would “grow” the color outward from visible pixels to prevent the “bleeding” in of weird colors when resampling.
Pre-multiplied alpha applies a composition pass on the the image, which is multiplying the color (rgb) values with alpha (keeping alpha value intact!).
This effectively makes all fully transparent pixels black, and very transparent pixels very dark. This is ok because these values get added to the destination pixels during compositing, being part of the weighted sum (S x alpha)+(D x (1-alpha)) where S and D are source and destination colors. In per-multiplied alpha we store the color S’= (S*alpha) along with the untouched alpha value, this means we only have to calculate (S’ + D x (1-alpha)) during composition.
So why would you use this premultiplied format? It only really removes info and saves a dumb multiply. One of the cool things is that you can “make” pixels that do more that just blending. For instance a pixel with alpha=0 should be black for blending, but you can just fill in a color anyway, and looking at the formula above, it would result in an additive effect(!). By being smart with values, you can make a pre-multiplied image that blends and brightens the image at the same time. You can imagine how useful that is for stuff like magic, fire, lasers etc.
And just some added info: lots of GPUs and texture formats still have a premultiplied alpha mode, as this was a big deal in early rendering. Nowadays people now just manually do most of these effects, there isn’t really any need to be smart about this stuff and just have more layers instead.
man, I love this guy. nice!
as a vfx artist who has sat through so many explanations of alpha and transparency… this is the best version that doesnt try to dumb it down but could still be understood by a layperson
The whole silver paint on half his head weirds me out and I can’t watch him.
Captain Disillusion is amazing as always.