|
crowd sourcing the experts |
|||||
| |
|||||
 |
|||||
(Page 3 of 3 pages for this article < 1 2 3) Filed under: What is YUV?
Using the “knob” graphic from my last post, here’s what a set of control knobs would look like for an 8-bit YUV signal: The Y knob has 256 steps, from 0-255, and the U and V knobs range from -128 to +128. Most major video formats - MPEG-2, AVCHD, DVCPROHD, H.264, XDCAM - all use YUV color space. The pixels are all stored using some variant of Y, Cb, Cr. There are 10-bit and 12-bit versions of YUV as well, and they also behave similarly to 10/12 bit per channel RGB. When effects are used on a video frame, sometimes the effect needs to convert the values back to RGB before the effect can be applied. In 8-bit or 16-bit-per-channel color space, there can potentially be “rounding errors” when performing this calculation. There are YUV color values that, when converted to RGB, could create negative values. That can’t happen in 8-bit or 16-bit values. This can mean situations where pixels that should pass through an effect unchanged will, in fact change in an unwanted way. Effects in Premiere Pro that have the YUV logo do the processing directly on the YUV values without converting them to RGB first. At no point are the pixel values converted to RGB, and you won’t see any unwanted color shifting. 32-bit-per-channel color space has the color precision to convert cleanly from YUV to RGB, and will not cause any of these rounding errors. In Premiere Pro, all of the 32-bit effects are “safe” to use. Let’s look at the same examples from my last article:
2. A DV file with a blur and a YUV color corrector exported to DV with the max bit depth flag. We will import the 8-bit DV file, apply the blur to get an 32-bit frame, apply the color corrector to the 32-bit frame to get another 32-bit frame, then write DV at 8-bit. The color corrector working on the 32-bit blurred frame will be higher quality then the previous example, and again, the signal path is pure YUV. 3. A DV file with a blur and a color corrector exported to DPX with the max bit depth flag. We will import the 8-bit DV file, apply the blur to get an 32-bit frame, apply the color corrector to the 32-bit frame to get another 32-bit frame, then write DPX at 10-bit. This will be still higher quality because the final output format supports greater precision. AND, the signal path again is pure YUV. 4. A DPX file with a blur and a color corrector exported to DPX without the max bit depth flag. We will clamp 10-bit DPX file to 8-bits, apply the blur to get an 8-bit frame, apply the color corrector to the 8-bit frame to get another 8-bit frame, then write 10-bit DPX from 8-bit data. YUV as well. 5. A DPX file with a blur and a color corrector exported to DPX with the max bit depth flag. We will import the 10-bit DPX file, apply the blur to get an 32-bit frame, apply the color corrector to the 32-bit frame to get another 32-bit frame, then write DPX at 10-bit. This will retain full 32-bit YUV precision through the whole pipeline. As you can see, Premiere Pro really tries to keep color fidelity, and by using either YUV or 32-bit effects, you can be sure that the color in your video is as accurate as possible.
(Page 3 of 3 pages for this article < 1 2 3) 
You must be registered to comment. This is an effort to reduce spam. Please REGISTER HERE.
|
|
||||
Disclosure, to comply with the FTC’s rules 16 CFR Part 255 This article was either written by Adobe employees or for Adobe by an outside contractor. It is intended for the Adobe Channel on ProVideo Coalition, which Adobe sponsors.
Copyright © 2012, HD Expo, LLC a division of Diversified Business Communications. DBA Createasphere
All rights reserved. HD EXPO, High Def EXPO, Createasphere, E-Tech, Entertainment Technology Exposition, 3D Production Workshop, VariCamp, P2 Camp, ColorCamp 101, and Lighting, Filters & Gels for HD are all trademarks of HD Expo, LLC.