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Daniel Brown

GH4 Guide: Master Pedestal Causing Banding and/or Red Rainbowing

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I've been trying Andrew's recommended photo styles enclosed in the GH4 Guide. It seems that the "C3 - Flat" settings can cause banding and a red rainbowing effect on gradient backgrounds.

 

I'm also on DVXUser and we've been discussing the issue and trying to figure out what could be the cause. It appears to be the fact that Master Pedestal is pushed to +15. I'm both trying to report possible issues and figure out fixes.

 

Here's a screen grab of the shot: [Graded] - [Ungraded]

 

I also cooled down the image which helped a bit.

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I don't see a banded transition between bit-depth levels, nor do I see any "rainbowing."

 

If it were an actual banded transition between bit-depth levels, the trasition would appear sharper, and we wouldn't see all that gradation within the area in question -- there would just be more bands instead of gradation.

 

It looks like a cast shadow from the subject onto the background. The "banding" that you might perceive is probably the umbra and penumbra of the cast shadow.

It appears that you were using a large, softer and cooler source (possibly daylight balanced) and that there was warmer ambient light (possibly tungsten balanced) filling the cast shadow.

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Remember you're shooting 8bit 4:2:0 - unless you are exporting 10bit - I wouldn't shoot against this uniform, neutral background, this is the worst case scenario for noise. I would go brighter, pure white even, because you can still get macroblocks as you go darker against a uniform wall like that. 

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I did say to light your backgrounds better. :P

 

I've seen this happen when the first time photographer (or seasoned photographer gets lazy, don't ask me how I know) uses only one or two lights and doesn't adequately light the background. This gives a shadow that when pushed in post gives ugh results, even in raw.

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The problem is 8-bit and noise when colors are pushed and the the contrast is accentuated, which accentuates the color of noise.  If you must work with the footage, you can try noise reduction before the grade.  If your noise reduction tool lets you profile the problem areas, maybe that would be better.  You can re-add grain later if needed.  

 

If the subject doesn't move at all, you have Photoshop CC, you can run videos through Camera raw filter, put a feathered mask outside the subject, and get really heavy handed with noise reduction and 0 the saturation.

 

Best to reshoot with a stronger fill light.

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We were under a time crunch, so the video got pushed out. It was in fine condition for where it was being shown. Plus it was motion graphic heavy, so it made up for some of the mistakes. The final word was that the banding and errors were due to [A] Lighting and  It's an 8-bit 4:2:0 image. Anyways...

 

Quick question regarding the Master Pedestal. Everyone I've talked to says that pushing the Master Pedestal to +15 or up at all will negatively effect the image and is counterproductive for color, noise, etc. Andrew says this is the way to do it for a flat image though (would really like your input on this Andrew).

 

What is everyone else thinking about the usage of Master Pedestal?

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The problem here is not to do with the master pedestal. The +15 setting helps the image by pushing the blacks away from the region of the encoding which doesn't get allocated enough bitrate. I have had consistently great results with it and wouldn't recommend it in the book if I thought it negatively effected the image.

 

It's important to learn how to grade an image properly as some of the colour cast issues here are easily fixed and adjusting the RGB curves would help too. Increase contrast in the image and dither the banding areas.

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Guest Ebrahim Saadawi

I found that raising the master pedestal to +15 helps in retaining more information in the shadows, and has no negative effect as far as I can tell.

It's just pushing the the bottom of the luma curve up to brighten the shadow areas. Below 0 crushes the blacks and loses information.

It does require colour grading in post though, so if you want a correct, deep black point straight of the card, then by all means do it in-camera.

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