u/aaka3207in r/compsci • Recommends
I just finished College Trig for my CS major, and this is the first instance of it i've seen applied in CS.
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#jpeg#discretecosinetransform#dct
JPEG DCT, Discrete Cosine Transform (JPEG Pt2)- Computerphile
Computerphile
2.6M subscribers • 66 videos on Hallway
- Recommended by 7 people: 6 on Hacker News and 1 in engineering communities.
- A classic. People kept recommending it from 2015 to 2026.
- Presented by Mike Pound, University of Nottingham
Intermediate. Assumes working knowledge.
697K views11 years ago7 recommendations
Computer scienceGraphics and audioRenderingAlgorithmsMath for programmers
Mike Pound explains how the Discrete Cosine Transform works and why it is the key to JPEG image compression.
DCT is the secret to JPEG's compression. Image Analyst Mike Pound explains how the compression works. Colourspaces: youtu.be/LFXN9PiOGtY JPEG 'files' & Colour: youtu.be/n_uNPbdenRs Computer That Changed Everything (Altair 8800): youtu.be/6LYRgrqJgDc Problems with JPEG: COMING SOON Upside Down Trees (Huffman Encoding): youtu.be/umTbivyJoiI Colourspaces: youtu.be/LFXN9PiOGtY JPEG isn't a file format - JPEG pt1: youtu.be/n_uNPbdenRs Upside Down Trees (Huffman Encoding): youtu.be/umTbivyJoiI Problems with JPEG: COMING SOON! Computer That Changed Everything (Altair 8800): youtu.be/6LYRgrqJgDc facebook.com/computerphile twitter.com/computer_phile This video was filmed and edited by Sean Riley. Computer Science at the University of Nottingham: bit.ly/nottscomputer Computerphile is a sister project to Brady Haran's Numberphile. More at bradyharan.comWhy it's here
7 people recommend thisWhat people say. Highly recommended as one of the clearest and most accessible explanations of the Discrete Cosine Transform.
Moments people linked to
netsharcon Hacker News • Recommends
On “How JPEG works: Interactively explore JPEG's lossy compression methods”
There's a series of videos showing the algorithm: link I finally understood DCT after watching link to this video And someone created a "JPEG to PNG" tool that "finds the smoothest possible picture that encodes to the given JPEG file": link . I tried it with some very terribly compressed images, and the outputs were a lot better.
greggmanon Hacker News • Recommends
On “The Pixel Factory”
…sights. It seems more like someone was asked to do a presentation, didn't have a solid idea of what to talk about, and so threw together a bunch of stuff until it filed their allotted time. I'm not trying to be discouraging. A great presentation can go a long way to making things understandable. For example this video explaining jpeg worked for me link to this video My point is only that fancy graphics and animation are not enough. The presentation actually has to get it's points across. Maybe this one worked for everyone but me but it didn't really work for me. I don't really know what to suggest to make it better. Maybe it all made more sense live with more talking. There were a few "bugs" For exampl…
walagranon Hacker News • Recommends
On “Discrete Cosine Transform in Video Compression – Explain Like I'm Five”
Pretty cool! I would add Computerphile's Youtube Video as a watch after this: link to this video . This is a part of their 4-video series on JPEG: link
skywal_lon Hacker News • Recommends
On “Video Codec in 100 lines of Rust”
The Computerphile channel has a nice series of videos on JPEG and one focusing on DCT 0. It's a nice ans easy intro to the subject. 0: link to this video
boolemanceron Hacker News • Recommends
On “Technical Overview of AV1 Spec”
There is a good video1 from the Computerphile channel describing the concept in the context of JPEG. 1 link to this video
itishappyon Hacker News • Recommends
On “VideoGigaGAN: Towards detail-rich video super-resolution”
It receives information about the spacial frequency content of the image. If you're unfamiliar, it's definitely worth looking into the specifics of how this works, as it's quite impressive! Here's a few relevant Wikipedia articles, and a Computerphile video: link link link to this video
u/minnoMight know what he's talking about | Cryptoin r/compsci • Mentions
On “What's up with these compression patterns? (more info in comments)”
This video gives a demonstration of how you don't change an image as much when you compress high-frequency information.
u/Rhomboidin r/compsci • Mentions
On “jpeg lossy compression, from what i understand is it looks for high frequency colors, but then what does it do?”
You're thinking of the wrong kind of frequency. JPEG doesn't know anything about wavelengths of light. Frequency in this context means spacial frequency, as in how rapidly the intensity of a single channel varies from right to left or up to down as you move throughout the image. For example, a sharp transition (like black text on a white background) contains very high frequencies, while a smooth gradient contains low frequencies. And this is measured in two independent dimensions, i.e. it would be possible for a given macroblock to have, say, lots of high frequencies in the vertical component while having few in the horizontal component.
Here are the 64 basis vectors for an 8x8 DCT tran…
u/Syntaximusin r/compsci • Mentions
On “What's up with these compression patterns? (more info in comments)”
Oh no, I'm fully aware that mpeg will have artifacts. But these aren't random artifacts like I would have expected with mpeg; for one thing, they're in perfect squared sections and they all have patterns, similar to what you'd see with jpeg.
I was thinking maybe this was compressed as a jpeg BEFORE it was compressed again in mpeg, which is what completely ruined the static noise.
Here's a different video that, aside from having a crap frame-rate, has completely different artifacts: link to this video
u/DRIESASTERin r/compsci • Mentions
On “What were your favorite college classes?”
I'd say start learning about jpeg, it uses a lot of compression technologies and a decent amount of math. After that you'll kinda know where to go i'd say.
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