MeGUI x264 CRF Lower Quality in Darker Scenes with Subtle Color Differences

[Pilotwings_64]

I'm searching for MeGUI presents that will allow me to convert my FRAPS captures to videos that strike a good balance between archival quality and manageable bit rate. I have found a few that seem to work well in lighter areas and in darker areas with strong color contrast. Finding presets that perform well in lighter scenes has been easy. However, using those same presets, I notice much lower quality in darker scenes that contain areas in which the color contrast is very low.

I have included screen shot's below. This phenomenon can be seen on the wooden floor and the lower, wooden portion of the wall, even as upper portions of the images seem to remain much more true to the original. This is especially true of the "Low" quality x264, which is still about 7 GB per hour of video, before sound is added. The "High" quality x264 seems to produce a reasonably good, but not great, quality image, but the files using this preset tend to be about 25-30 GB per hour of video, before sound is added. This seems excessive. Is there a way I can clean up the quality in these types of dark scenes without resorting to extremely high bit rates?

Thanks in advance.



All of the x264 streams were encoded with 10-bit color, and the screenshots were taken using MPC-HC.

I was able to see the differences best by putting each image into it's own layer on the same Paint.NET file. That way I could toggle between any two images for comparison.


Original FRAPS Capture - 383 Mbps







High Quality 10-bit x264 - 95.7 Mbps
program --preset slow --crf 12 --output "output" "input"







Medium Quality 10-bit x264 - 60.5 Mbps
program --preset slow --crf 16 --output "output" "input"







Low Quality 10-bit x264 - 25.0 Mbps
program --preset slow --crf 22 --output "output" "input"

[jagabo]

Is there a way I can clean up the quality in these types of dark scenes without resorting to extremely high bit rates?

No. You can try using higher CRF values and setting aq-strength around 1.8 to 2.0. But in the end the result is higher bitrates.

[Pilotwings_64]

Thanks for the reply.

Is there any way I can set MeGUI to use one crf value when it encounters a scene like this and another value for all other scenes?

Thanks again.

[poisondeathray]

You can specificy zones in x264 (and megui) , so different CRF values (or bitrate multipliers), even some different encoding settings can be applied to different sections

[jagabo]

Oh sorry, I suggested setting qcomp in my last post. I should have said aq-strength. Try setting aq-strength to a larger value than the default 1.0. Around 1.8 to 2.0.

[Pilotwings_64]

Thanks for the suggestions. I have not been able to get the quality I want by changing the aq-strength. After reading up on the subject, I think I'm going to have use zones, as poisondeathray suggested.