Forgot your password?
typodupeerror

Comment: Gamma and sRGB (Score 4, Insightful) 368

by smasch (#31254802) Attached to: Scaling Algorithm Bug In Gimp, Photoshop, Others
The basic issue here has to do with gamma curves and the way they're being handled (they're not).

Most image files on your computer (BMP, JPG, PNG, etc.) are stored in the sRGB color space. sRGB defines the use of a gamma curve, which is a nonlinear transformation applied to each of the components (R, G, and B). The issue here is that most scalers make the assumption that the components are linear, rather than try to process the gamma curve. While this does save processing time (undoing the gamma curve then redoing it), it does add some error, especially when the values being scaled are not near each other.

So does this matter? Well, in some pathological cases where there are repeated sharp boundaries (such as alternating black-white lines or fine checkerboard patterns), this would make a difference. This is because the linear average of the pixels (what most image scalers use) yields a different result than if the gamma value was taken into account. For most images (both photographic and computer generated), this shouldn't be a big problem. Most samples are close in value to other nearby samples, so the error resulting from the gamma curve is very small. Sparse light-dark transitions also wouldn't be noticeable as there would only be an error right on the boundary. Only when you exercise this case over a large area does it become obvious.

One final point: this gamma scaling effect would occur regardless of the actual scaling algorithm. Bilinear, bicubic, and sinc would all have the same issue. Nearest neighbor interpolation would be unaffected, but in these cases, the output would look far worse.
Censorship

Chinese Censor-Beating Software Resembles Malware, But Isn't 160

Posted by timothy
from the good-to-know dept.
coondoggie writes "Software designed to beat Chinese censorship may behave in ways that seem suspect, but it is all part of the application's strategy to fool the Great Firewall of China, according to one programmer of the software. 'There are many built-in tricks that do all kinds of things to confuse the firewall,' says David Tian, a scientist for NASA who works spare-time on UltraSurf, the free software designed to promote unrestricted Internet access for citizens of China persecuted for being members of Falun Gang, the religious group the Chinese government is trying to suppress."

Everything that can be invented has been invented. -- Charles Duell, Director of U.S. Patent Office, 1899

Working...