Urgent compression disaster

[gilleklabin]

Hello Red Users,

I recently directed a video and sadly me and DP are left here wanting a beautiful file version of the promo and we're going crazy trying to find the right kind of compression. It was a low light shoot and it seems to me that every time we compress the file we get disastrous banding and noise in the frame, around the background smoke and light. There are banded artifacts around the lights and anywhere where smoke is being lit. (see pics 1 n 2).

I have attached frames from the 10 bit uncompressed HD version (4) and some from Apple's intermediate codec and some from proRes 422. we just want a full HD version, or even a 720p version but we can't seem to get the compression right.

any help would be of huge value to us as we're close to tears

thanks in advance
Gille

[BradWright]

Hello Red Users,

I recently directed a video and sadly me and DP are left here wanting a beautiful file version of the promo and we're going crazy trying to find the right kind of compression. It was a low light shoot and it seems to me that every time we compress the file we get disastrous banding and noise in the frame, around the background smoke and light. There are banded artifacts around the lights and anywhere where smoke is being lit. (see pics 1 n 2).

I have attached frames from the 10 bit uncompressed HD version (4) and some from Apple's intermediate codec and some from proRes 422. we just want a full HD version, or even a 720p version but we can't seem to get the compression right.

any help would be of huge value to us as we're close to tears

thanks in advance
Gille

Here's a couple of things I would suggest. First, don't use AIC for anything. AIC is an 8 bit codec. Converting from 12 bits to 8 bits is a very difficult process. Tons of grey shades will be lost in the processes.

In the original 12 bit Red Raw image, there are 4096 shades of grey between absolute black and the brightest white. When you reduce the image to 10 bit you have only 1096 shades of grey. When you get to 8 bit you have only 256 shades of grey. What this means is that black and white images suffer the most. Those very subtle grey shades often become big swaths of solid color banding.

What you will likely need to do is color grade the image, so that the image has more contrast. You want the transition between light and dark to take up less pixels on the screen. This way the viewer's eyes won't see the giant bands of color. Adding blur in the transition areas can help, as well.

I wish you all the best of luck with it. You've sort of hit the worst case situation for color compression.

[Jeremy Neish]

I have a lot of experience in video compression (been doing it since QuickTime 1.0). If you'd like some help, I'm willing to give it a shot and see if it's possible to reduce the banding. However, since you are presumably trying to reduce the bitrate considerably from what started out as virtually lossless, the loss of those bits has to show up somewhere and depending on the nature of the footage banding can be hard to eliminate completely.

[gilleklabin]

Hi Guys,

thank you so much for your maths Brad, kind of puts my mind at ease. since posting i have exported a 720p 4:2:2 version of the video using the Sheer 10bit uncompressed codec and it looked worlds better.

Jeremy, out of curiosity what would you have tried in order to fix the problem? as this is only for our own versions of the file (the band have taken delivery on DVD of all things) i wouldnt want you to waste your time on it.

thanks again guys,

you make reduser great

Gille

[Dominic Jones]

Well, you shouldn't really have problems going from RedCode to a decent, high-bit-depth uncomp HD codec.

You don't state what your current workflow is, so hard to nail down where you're hitting the problems, but try a conform via Crimson (you're cutting on FCP, no?) to RedCine, then export to one of the AJA or BlackMagic codecs (free to download if you don't have them). BM do a great 10-bit 4:4:4 uncompressed codec that really shouldn't show any banding. Use a downsample filter that's kind, like Lanczos or Mitchell...

If you don't have Crimson, just try the odd shot through RC to see what the output looks like. I would have also thought that the 10-bit 4:2:2 codec should look good, too.

Good luck, nice looking shots if you can solve those issues...
Dom.

EDIT: Looks like I just missed you! Glad to hear you got it looking better...

[Cail Young]

Worst case you may need to add noise or grain in the tool of your choice.

EDIT: Side note - awesome lighting.

[Emery Wells]

I second Calis recommendation. Adding a tiny bit of noise to the image will break up the banding almost completely. It's a commonly used trick and it works quite well.

[doyneditmas]

Thanks Guys for your tips!! I shot the above promo and its a shame that the compression is unable to deal with the backlit smoke in shades of grey and you get this horrible banding, Brad's post does explain why although I have looked at a movie trailer shot in B+W in Apple HD 720p which I believe is encoded with H.264 and it looked fine. When we try to go from 10bit uncompressed to ANY of the compressed formats PRO RES, H.264, Photo JPEG etc this horrible artifact rears its ugly head yet none of the trailers on Apple seem to suffer from the same compression they all look fabulous? Is this a RED anomoly?

Again thanks for all your help!!

The best we can get is keeping it in 10bit uncompressed with the Sheer Codec.


Hamish

[conrad gaunt]

Adding a little noise to the footage can help the codec distribute its quantization better. I used to do this during fade to black type shots to avoid banding.

[Stacey Spears]

Hopefully posting a link to another forum is not a voilation here. I really did not want to repost all of the images. http://www.avsforum.com/avs-vb/showthread.php?t=1011359

In the link above I show examples of noise shaping and dither to convert from high to low bitdepth. The first example is from an animation. It shows rounding vs. dither from 16-bit to 8-bit. The next example shows 10-bit to 2-bit. This is an extreme example to show the power of dither and noise shaping. Next up are some examples of linear vs. non-linear scaling.

In your example, banding may be occuring from high to low bitdepth as well as from compression.