REDrushes and the debayer quality
By S Simmons. Filed in Editing, Mac software, RED |
I’ve been enjoying the batch processing capabilities of REDrushes and as I was asked recently about the different debayer quality options I had a general answer to what the different quality levels mean but I had not done a side by side comparison. The debayering process converts the raw RED data to an RGB image for use in the video world so the higher the quality the better the image, at least in theory. When you do side by side comparisons with the same footage there are some subtle differences in quality.
The image below is from a 4k clip converted with REDrushes and the Full Res debayer setting to a 1920×1080 ProRes 422HQ file (click on the images for a larger view):
The next image below is the same part of the same frame of a 1920×1080 Prores 422HQ file that was debayered at Quarter resolution:
It’s a bit tough to see here on the web but the quarter rez debayer has noticeably more noise. It’s not extreme but it’s enough that you probably would lose some latitude when doing a color correction, especially if you were pushing the image. It also takes a LOT longer to render the full debayer.
The other place it would be most noticeable is around edges. You really begin to see the difference in the quality levels when you apply a difference matte between the two examples (click on the images to open a larger version):
Again, it’s very tough to see in this low quality web image and it depends a lot on the monitor you are viewing on but if the light isn’t too bright on the screen and you get really close (click on the image above for a larger view) you can really see the outline and edges on the slate. Here’s an exaggerated version:
Is there that much of a loss that it’s worth the extra time and effort to debayer at full rez? It might be more of a mathmateical question for the programmers as to what you really gain from full rez and as I’m an editor and not a colorist I don’t really know the answer (maybe a colorist or two will chime in via the comments) but if you can see that much difference in the matte above then that seems to me like loss enough to debayer at full rez for the final online. For the most dramatic example render you own footage with REDrushes at the two extremes of debayer quality, slap them in the a timeline, apply the difference matte (thanks Jon) and then render the full moving image. When the footage starts moving you can see even more.
