Transforms for Video Compression, Part 1: Vectors, the Dot Product and Orthonormal Bases The use of transforms in data compression algorithms is at least 40 years old. The goal of this three-part series of posts is to provide the mathematical background necessary for understanding transforms and to explain why they are a valuable part of many compression algorithms. I’ll focus on video since that’s my particular interest. Part… View Article
Rolling CMOS Shutters and Curved Wiper Blades One time last winter I shot a photo with my camera phone out the windshield of my car and got a strange image with curved wiper blades: No, my wipers don’t look like this! I’ve been meaning to track down the reason why this happened. It is clear that cellphone cameras don’t usually use mechanical… View Article
If Only We Had Better Test Content… I just saw this news about research that says you notice compression artifacts less if you like the content of a particular video clip: Using four studies, Kortum, along with co-author Marc Sullivan of AT&T Labs, showed 100 study participants 180 movie clips encoded at nine different levels, from 550 kilobits per second up to… View Article
Creating Single-Frame Movies My camera (an Olympus SP-570UZ) allows me to optionally record a four-second audio clip with each photo I take. I haven’t used this feature much because I typically upload my photos to Flickr, and there’s been no good way to associate the audio with the video. Ideally, I would like an audio player to appear… View Article
The Basics of 3D Image Acquisition One of our clients is heavily involved in 3D video and has been for several years. However, several are just now starting to think about it because of the uptick of interest in the consumer electronics world. Enough questions have been posed to us recently that it seemed worthwhile to me to pull together a… View Article
Thoughts on 3D After NAB I just returned from this year’s NAB show, where I was bombarded with 3D demos in virtually every booth. Most of the factors driving this 3D superabundance originate outside of the broadcast industry itself. First, TV manufacturers are hot on 3D as a way to get everyone who just bought an HDTV to upgrade to… View Article
Encoders Aren’t Commodities My partner Ben Mesander had a really cool post the other day: An H.264 encoder written in 30 lines of C code. Ben’s encoder outputs completely valid H.264, but it doesn’t actually compress anything. (What do you expect from 30 lines!) In fact, because of the necessary H.264 headers, the output of Ben’s encoder is… View Article
The Math Behind Analog Video Resolution The world is moving in the direction of HDTV, but NTSC “standard def” signals are still common for many reasons and will remain so. One important reason is that cameras that output NTSC are widely available and cheap! Many applications, including a lot of security applications, simply don’t require the resolution of HDTV — and… View Article
On the Importance of Encrypting Video This morning brought a front-page Wall St. Journal article that’s a bit of a jaw-dropper: Militants in Iraq have used $26 off-the-shelf software to intercept live video feeds from U.S. Predator drones, potentially providing them with information they need to evade or monitor U.S. military operations. … The potential drone vulnerability lies in an unencrypted… View Article
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