Very interseting solution to address the 8 bit banding issue

danyyyel

I have read this very interesting article link below on how to mitigate the banding issue. It has been said before but this clearly shows the result of using higher ISO that bring some noise that breaks the banding. I had started to experiment a bit with it but had no time lately, but I think the example in the post is very revealing. I hope to do some test on sky banding when I have some time to see if it works as good as in kholi wall example.

http://www.campcomet.com/archives/797

Noise. NOISE. Bad word, right? Most people hate digital noise and will do anything to avoid or remove it from their footage. The first, and seemingly most obvious choice, is to shoot at a lower ISO which tends to exhibit less noise in most digital cameras. However, as is with everything in life–generally, there are trade-offs… some you may not initially notice lurking around in your footage until you get to post.

One of these threats is Noise’s equally ugly older sister: Banding.

When the D90 and GH1 first dropped, one of the stand-out features was being able to utilize a various array of ISO increments to adjust for lighting situations. In ultra lowlight, some are brave enough to jam the ISO up to 3200. In broad daylight? Right on down to 160 (or 100 on Canon DSLRs). Unfortunately, the cleanliness and smoothness of a low ISO setting opens a gateway for banding to creep into your image.

Vitaliy_Kiselev

@danyyyel

Can you, please, add core idea to you post?

danyyyel

Did it above, hope it is ok.

balazer

If you want to use noise to cover banding, do it in post, where you have more control. No need to shoot at high ISOs just for that.

edit: Nevermind. After what Mark_the_Harp said, I realize that my idea wouldn't work very well. The noise needs to be introduced before the quantization. Adding the noise after would require a lot more noise to hide the banding.

kholi

@balazer

You're pitching to "mask" banding in post with noise (nothing new), but I must ask... Have you actually tried it? =]

I should've clarified as well, it's for those who are going to go to grade. You do not want to add "noise" step, go to DPX, then grade, and you certainly do not grade before you add noise.

If you're going straight out of camera to the internet, sure, you COULD use a noise layer but it's going to look worse than just dealing with it in camera. The dB needed to mask banding of the GH2 nature is much more drastic than what's going to go on in post.

LPowell

@danyyyel
The conversion from AVCHD to ProRes4444 with 5DtoRGB is what will reduce the banding (posterization), which is inevitable with the 8-bit 4:2:0 AVCHD color space. The GH2's read noise actually decreases as you increase ISO, though the dynamic range decreases even more so:

http://www.sensorgen.info/PanasonicDMC_GH2.html

As ISO goes up and dynamic range goes down, quantization of sensor noise becomes coarser. This may make the noise look more noticeable, even when the exposure is kept constant.

kholi

@LPowell

Thanks for explaining that. You also have a point about 5DtoRGB reducing amounts of posterization happening. It's very evident even with 422 through 5DtoRGB in comparison to Log and Transfer of the same ProRes flavor. Even more reason to stick with 5DtoRGB for image sensitive projects.

Do you know if the ISO to DR trade-off transfers over to video mode as well? I know it does for stills, but has anyone thoroughly tested video mode?

Also, do you know how color latitude is affected as you increase or decrease ISO? I have a feeling that lower ISO = more color Latitude, which may also account for the appearance of a larger range.

Thoughts?

lolo

to hide banding on an editor what i do is that i duplicate the video layer, then i key the section that has banding (must likely the sky or a wall, so is not a big deal as must likely it will be of one color mostly) on the upper layer, and then on the lower layer i add a fast blur of 1 to 3 pixels...

or something similar with masks and keys if the section that has banding is from the same color than a subject or other interesting stuff...

LPowell

@kholi
Yes, the decrease in DR as ISO is increased is an inherent property of the image sensor. It happens in video mode just as in still mode. Latitude at the dark end of the range is determined by how much light reaches the sensor through the lens. It will increase by up to one stop as the shadow noise decreases with high ISO's.

Meierhans

While its denoising features are only average, I found Magic Bullet Denoiser (the old one.. not sold anymore) to
work very well against banding. I had a really bad case of underexposed 7D footage that showed strong banding in the sky after CC. By using a combination of chromakey & MB Denoiser I could fix it completly.

Ralph_B

@lolo
Good technique. Thanks for sharing.

ronnylov

The technigue to add slight noise to reduce banding is called dithering.
Here is an interesting discussing of the topic denoising and debanding:
http://forum.doom9.org/showthread.php?t=153589

And here is the solution with the avisynth plugin dither: http://forum.doom9.org/showthread.php?p=1386559#post1386559

lolo

@Ralph_B :), you are welcome

P4INKiller

@ronnylov

Yup, dithering is pretty much what you want to do.
You're basically adding noise that correspond to the colors in your image, affecting only bands of lines while having a lesser effect on smooth gradients.

Mark_the_Harp

Isn't dithering adding noise before quantizing, not afterwards? Which is why high ISOs hide the banding. Not knocking these solutions but just saying...

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