When looking at stills from video and film footage, it appears that the "B" channel (from RGB) always contains the most amount of grain. I'm going to test out some methods of degraining only the Blue channel in order to determine if this might be a way to denoise without overly smoothing the image. I'll report back in a bit
Blue
Green
Red
From http://www.joemaller.com/fcp/fxscript_yuv_color.shtml
"Some deeper research into YUV reveals two reasons why Blue always looks so crummy when extracted from video images. The U channel ranges from Red to Yellow, the V channel ranges from Blue to Yellow. Because Yellow is Red and Green, Red is essentially sent three times, Green twice and Blue only once. Reconstructing the Luminance component reveals another reason Blue suffers, the Blue channel is only 11% of Luminance. "
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Hope replying to myself is OK. I'm not trying to bump the thread
Here are some test results. Unfortunately, the conversion to Xvid smooths out some of the differences.
Original Clip
original_xvid.avi
Blue Channel Only
blue_xvid.avi
Blue Channel Filtered
blue_filtered_xvid.avi
Output with Filtered Blue Channel
final_xvid.avi -
The thing is, the blue channel is allowed to include the most noise, because we (humans) are least sensitive to blue. That's why the colour encoding equations are the way they are.
Broadcast monitors have a "blue only" button to allow engineers to easily see how horrible the signal really is. As you say, because of the encoding, blue looks worse first, but this is only visible to human eyes when looking at the blue channel on its own.
Cheers,
David. -
This is one reason green is used for chroma key from encoded video. Blue is too noisy.
In the studio (e.g. newsroom), full bandwidth clean RGB is sent to the chroma keyer direct from the camera's CCD processing (before matrix and encoding) to provide clean keys from blue.
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