Daniel Brown Posted July 18, 2014 Share Posted July 18, 2014 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. Quote Link to comment Share on other sites More sharing options...
tupp Posted July 18, 2014 Share Posted July 18, 2014 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. Daniel Brown 1 Quote Link to comment Share on other sites More sharing options...
sunyata Posted July 18, 2014 Share Posted July 18, 2014 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. Daniel Brown 1 Quote Link to comment Share on other sites More sharing options...
johnnymossville Posted July 18, 2014 Share Posted July 18, 2014 The problem is mostly chalked up to 8bit. You really picked a really tough shot to shoot right there didn't you? Daniel Brown 1 Quote Link to comment Share on other sites More sharing options...
leeys Posted July 19, 2014 Share Posted July 19, 2014 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. Daniel Brown 1 Quote Link to comment Share on other sites More sharing options...
varicam Posted July 19, 2014 Share Posted July 19, 2014 Or use a green screen. :) Quote Link to comment Share on other sites More sharing options...
Michael Ma Posted July 19, 2014 Share Posted July 19, 2014 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. Daniel Brown 1 Quote Link to comment Share on other sites More sharing options...
Daniel Brown Posted July 20, 2014 Author Share Posted July 20, 2014 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? Quote Link to comment Share on other sites More sharing options...
hmcindie Posted July 20, 2014 Share Posted July 20, 2014 It looks like compression artifacts. I don't know why people keep claiming this an 8-bit issue when you can clearly see the compression destroying the image noise with little blocks. 10-bits won't help with h264. Quote Link to comment Share on other sites More sharing options...
Administrators Andrew Reid Posted July 20, 2014 Administrators Share Posted July 20, 2014 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. Quote Link to comment Share on other sites More sharing options...
Guest Ebrahim Saadawi Posted July 20, 2014 Share Posted July 20, 2014 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. Quote Link to comment Share on other sites More sharing options...
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