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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

blue sky and clipping

Philip Powell

Philip Powell

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I've kind of noticed this in a few other shots and wondered if anyone else has.

Often, when shooting a blue sky a portion of it will clip(in the blue channel). And the transition from this blue channel clipped area to the non clipped area creates artifacts. It winds up looking like a noisy steak across the sky, transitioning from the Blue channel clipped areas to the non-clipped areas. (not a useable shot as a consequence.)

The shot looks great other than that. But based on my quick tests, I would say that when shooting a blue sky you can never let the blue channel clip.

I don't have my polarizer yet, otherwise I would test to see if that helps.
 
I don't think the pola will help, but are you using any ND filters?

I haven't experienced this problem but I do shoot a lot of sky here in the middle of the ocean. I have to use ND.
 
it might be the same thing we experienced today. Can you post pics? If it is the same issue I'll post sample footage too.
 
It winds up looking like a noisy steak across the sky...
Click to expand...

Is that anything like "the cow jumped over the moon?" Or were you badly quoting Thomas Pynchon?

But seriously, there are a lot of factors that affect whether a polarizer will help or not (time of day - there is 75 degree difference in the field of polarization between high noon and sunset; ratio of forground objects to background objects; whether or not glare, translucense, reflectivity, contrast are desired or not; matching other shots, etc.). But they will also act to a degree as an ND filter.

As it's the blue channel that's clipping, you may better off with a UV or haze filter since it may be the UV that' causing the clipping since you say the shot looks okay otherwise. At the extreme, try a skylight filter. A UV filter is colorless because it is blocking the uv light outside of human perception (but camera sensors still see it). Haze filters are slightly yellowish to counter too much scattered blue light. Skylight filters take this a step further and are pink or amberish to cut the blue even more and warm the shot.
 
stills of it

stills of it

Here is a shot of the blue channel and one of the full RGB. It's only at that transition point that things look poor. I've increased the contrast on the RGB one so that the issue can be seen a bit better.
 
Yes, I have exactly the same problem, even more pronounced.
I thought that it is 16 bit to 8 bit conversion doing it, since when I watch it on 16 bit TIFF out to 12 bit screen I do not see it, or it is much less visible.
 
Of course skies clip. It's a regular CMOS sensor. Try the same shots with a DSLR and you will get the same result.

Grad NDs - or shooting during magic hours :) -are an option.
 
I could barely see these artifacts on the original image, but heres the curves totally screwed with...if this is the problem.
 
NateWeaver said:
I'm not seeing anything either, and I stared at the sky for 30 seconds.

I think this must be a display issue.
Click to expand...

Hmmmm...I must say I'm a bit perplexed. While I fully believe this is an actual issue, I do believe it's harder to see on some displays than others. In fact, on my home PC, viewing the jpegs I could just BARELY see the problem, while here at work, viewing the same jpegs it's obvious. (especially in the blue channel shot.)

Also, trust me when I say this isn't a banding issue, unfortunately I'm very familiar with what that looks like.

I will try and post some video shortly.
 
Sir Pancake said:
Hmmmm...I must say I'm a bit perplexed. While I fully believe this is an actual issue, I do believe it's harder to see on some displays than others. In fact, on my home PC, viewing the jpegs I could just BARELY see the problem, while here at work, viewing the same jpegs it's obvious. (especially in the blue channel shot.)

Also, trust me when I say this isn't a banding issue, unfortunately I'm very familiar with what that looks like.

I will try and post some video shortly.
Click to expand...

I analysed my video and I see on the histogram that I clipped the blue channel.
Then I backed it off a bit in post for color correction.
I wonder if I don’t touch the footage at all if this bending will pop up.
Have to try.
I don’t see it on my 16 bit TIFFs at all, do you see it on your TIFFs?
I see it only after converting from 4K->2K-> H.264 8-bit
Most laptops and LCD desktop screens are 32bpp it mean 3x8 bit plus 8 bit padding or possible 3x10 bit plus 2 bit padding (never seen this one though)

Yes on the 16 bit per pixel screens you see this bending big time, but I see it just a bit on the 32 bpp laptop screen as well, because I know what I am looking for.
But what you see barely on your laptop you will see very well on the 50” HD-LCD, try it.
Big time bending.
 
Do you have the original R3D file? I can convert it to uncompressed and take a look on my broadcast HD monitor for you.
 
Laptops do not have good contrast, also desktop LCDs.
But large LCDs designed for HD-TV do.
Turn up your contrast if you have adjustment.

I am just burning Blu-ray done with color space conversion set to ‘perceptual’ this one suppose to kill banding. Let you know in 5 minutes if it helped.
 
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