Chroma Clipping
- Thread starter Chadac
- Start date
Turning the chroma level way down seems to be doing the trick for me, too.
I just did a shoot with the following settings:
Film Cam PH 1080/25p
Detail -5
V Detail -5
Detail Coring -1
Chroma Level -4
Chroma Phase +1
Colour Temp ACH -1
Colour Temp BCH -1
Master Ped +2
DRS off
A iris 0
Gamma B-Press
Knee High
Matrix Norm2
Skin DTL ON
That's giving me something much more like the look I want without clipping on the skin tones so easily. Still seems to have limited ability to pull it around in post compared to the HVX200's DVCProHD, with posterisation still the main artefact that seems to crop up when I start pulling stuff around, but altogether much less dangerous on the skin tones thus far.... and may turn that Chroma level down even further!
Cheers, Hywel
I just did a shoot with the following settings:
Film Cam PH 1080/25p
Detail -5
V Detail -5
Detail Coring -1
Chroma Level -4
Chroma Phase +1
Colour Temp ACH -1
Colour Temp BCH -1
Master Ped +2
DRS off
A iris 0
Gamma B-Press
Knee High
Matrix Norm2
Skin DTL ON
That's giving me something much more like the look I want without clipping on the skin tones so easily. Still seems to have limited ability to pull it around in post compared to the HVX200's DVCProHD, with posterisation still the main artefact that seems to crop up when I start pulling stuff around, but altogether much less dangerous on the skin tones thus far.... and may turn that Chroma level down even further!
Cheers, Hywel
Barry_Green
Moderator
Glad to hear you're getting what you like out of it!
bgundu
Veteran
What would we do without Barry? Three cheers for Barry! Hip-hip horray!
PaPa
Major Contributor
Yeah, right now i'm sticking to the following settings, and it's leaving me with something i like.
Detail: -5
VDetail: -5
Chroma: -4
Coring: +1
Pedestal: 0
Gamma: CineD
Matrix: Norm1
I am quite pleased. But as you said, right now, the ONLY thing i don't like ( i've learned how to work around blowouts, and now they look awesome ) is the posterizing. If you have a solid colored wall, you really can't have any type of gradient low light going across it. Frustrating because that actually does limit you in terms of what kind of textures you can feed the camera.
But yeah, enjoying the hell out of this boy. Still very interested in seeing Barry's comparison between the AF100 and the GH2, however.
Detail: -5
VDetail: -5
Chroma: -4
Coring: +1
Pedestal: 0
Gamma: CineD
Matrix: Norm1
I am quite pleased. But as you said, right now, the ONLY thing i don't like ( i've learned how to work around blowouts, and now they look awesome ) is the posterizing. If you have a solid colored wall, you really can't have any type of gradient low light going across it. Frustrating because that actually does limit you in terms of what kind of textures you can feed the camera.
But yeah, enjoying the hell out of this boy. Still very interested in seeing Barry's comparison between the AF100 and the GH2, however.
Glad it is not just me PaPa, I agree that low light gradient across a solid coloured wall is the thing that is sticking out like a sore thumb for me, too.
I'm working on my production design (another invaluable tip from Barry about avoiding the "low budget indie film in a small white room" look) but- I'm shooting low budget indie films and there's only so much production design can do to hide these walls on my budget.
Still, compared with the list of things I had to avoid shooting with the Canons (brick walls, houses, tiles, water, stockings, striped blouses, jeans...) it is a big step forward.
Because I'm shooting 1080p but delivering 720p at the moment, I've found the "Reduce Banding" filter turned up close to max in FCP helps- this is basically adding noise to the image, but it helps given I'm downsampling as my final step. Apply this filter last in the chain, definitely after any sharpening and colour correction.
The footage does have different features from things I've used previously- I can see more noise in the deeper shadows (the mid to high tones are very clean) and more posterisation in the mid tones. Not unpleasant, easy to control the noise to any desired degree black crushing in post (which I always do anyway). Distinctive and different in character from the HVX200 footage- not really better or worse in character, just different.
Having got a handle on the skin tone blowouts it is really only that posterisation which is bugging me... anyone got a magic setting to avoid that? Probably can't have it simultaneously with other fave settings but would be good to have one on the dial for where you know posterisation is likely to be a problem.
Cheers, Hywel.
I'm working on my production design (another invaluable tip from Barry about avoiding the "low budget indie film in a small white room" look) but- I'm shooting low budget indie films and there's only so much production design can do to hide these walls on my budget.
Still, compared with the list of things I had to avoid shooting with the Canons (brick walls, houses, tiles, water, stockings, striped blouses, jeans...) it is a big step forward.
Because I'm shooting 1080p but delivering 720p at the moment, I've found the "Reduce Banding" filter turned up close to max in FCP helps- this is basically adding noise to the image, but it helps given I'm downsampling as my final step. Apply this filter last in the chain, definitely after any sharpening and colour correction.
The footage does have different features from things I've used previously- I can see more noise in the deeper shadows (the mid to high tones are very clean) and more posterisation in the mid tones. Not unpleasant, easy to control the noise to any desired degree black crushing in post (which I always do anyway). Distinctive and different in character from the HVX200 footage- not really better or worse in character, just different.
Having got a handle on the skin tone blowouts it is really only that posterisation which is bugging me... anyone got a magic setting to avoid that? Probably can't have it simultaneously with other fave settings but would be good to have one on the dial for where you know posterisation is likely to be a problem.
Cheers, Hywel.
Last edited:
Rick Burnett
Section Moderator
Which has me wondering, if you shoot with lower chroma values, does that translate to using up less colors in your 8-bit palette? I haven't had a chance to test it, but I am wondering how chroma settings affect the banding? Of course, trying to add those colors in after the fact is probably going to exacerbate the banding.
I wonder if anyone has written a plugin that tries to do pixel averaging across low differential spatial pixel values. Might be something neat to try.
I wonder if anyone has written a plugin that tries to do pixel averaging across low differential spatial pixel values. Might be something neat to try.
Stu Siegal
Well-known member
I wonder if Twixtor would recognize the banding as noise and smooth it out if you selected a large enough area. Don't own Twixtor or I'd give it a try.
Alpha Beta Omega
Veteran
Using HD norm (which is pretty flat) and Norm1 (which has some noise) should help to mask some banding issues.
I don't know if lower chroma = less colours from the 8 bit palette. My visual impression of the footage I shot with Chroma level -4 compared with 0 was that the most saturated primary colour stayed nice and bold and saturated, but it turned the wick down on the mid-saturation colours. Kind of like a gamma curve applied to the saturation rather than a reduction in overall "colour gain".
That probably would reduce the number of available colour choices for these gradients, but for me it seems to be a better compromise because it lets me get the skin tones closer to the 80% level where I like them to be without blowout, which means the rest of scene can be rendered more or less intact with minimal grade, at which point the camera seems to be doing a pretty good job. With the higher chroma levels I was having to underexpose to control the skin tone clipping, which meant pulling up and desaturating in post, which was definitely making the posterisation much more dramatic, as two tones which were originally almost identical would get pulled further apart in colour, making the quantisation much more obvious.
I'll try to do some tests next time I'm set up in the infinity cove by exposing for the skin tones with different chroma settings, seeing where the clip happens, and seeing what happens to a smooth background gradient. I don't have any calibrated charts for a more scientific approach I'm afraid! Will be a good experiment as I'm meant to be shooting some tutorial videos on the plain cove background next week.
I'll play with HD norm and Norm1 as well, although I much prefer the PAL-like colour rendition of Norm2 and the BPress look gets me closer to what I usually do in post, which has seemed a safer bet so far. I'll try the Cine-like gammas a bit more too as I never shot anything else on the HVX200 - maybe turning the chroma right down would give me more latitude to expose where I want to on those too.
Cheers, Hywel.
That probably would reduce the number of available colour choices for these gradients, but for me it seems to be a better compromise because it lets me get the skin tones closer to the 80% level where I like them to be without blowout, which means the rest of scene can be rendered more or less intact with minimal grade, at which point the camera seems to be doing a pretty good job. With the higher chroma levels I was having to underexpose to control the skin tone clipping, which meant pulling up and desaturating in post, which was definitely making the posterisation much more dramatic, as two tones which were originally almost identical would get pulled further apart in colour, making the quantisation much more obvious.
I'll try to do some tests next time I'm set up in the infinity cove by exposing for the skin tones with different chroma settings, seeing where the clip happens, and seeing what happens to a smooth background gradient. I don't have any calibrated charts for a more scientific approach I'm afraid! Will be a good experiment as I'm meant to be shooting some tutorial videos on the plain cove background next week.
I'll play with HD norm and Norm1 as well, although I much prefer the PAL-like colour rendition of Norm2 and the BPress look gets me closer to what I usually do in post, which has seemed a safer bet so far. I'll try the Cine-like gammas a bit more too as I never shot anything else on the HVX200 - maybe turning the chroma right down would give me more latitude to expose where I want to on those too.
Cheers, Hywel.
Thanks, Barry, this is no doubt the explanation for the AF100's color-shifted highlights that Art Adams pointed out in his ProVideo Coalition review:
http://provideocoalition.com/index....onic_af-100_the_good_the_bad_and_the_ugly/P1/
Here’s my biggest complaint about clipping on the AF-100:
Those brake lights aren’t supposed to be orange. They’re an orange red, and while most other cameras would render them as clipped red this camera seems to say to itself, “I see a clipped red channel and a clipped green channel, so I’m just going to mix those two clipped values together.” When you mix red and green you get orange. It’s not an attractive look.
I also appreciate your analysis of the GH2's compression of color saturation when it approaches overexposure in non-Cinema modes. While this isn't a technically correct way to handle clipping in a single R, G, or B channel, it at least pushes the blown highlights toward white, which produces a more natural-looking type of color shift in most cases.
I think this phenomenon points out an inherent fallacy in the theoretical design of camera sensor Bayer Filters. The RGBG filter array they contain will inevitably produce inaccurate color shifts whenever any single color sensor clips from overexposure. This can easily occur with the high intensity, pure-color stage lighting used in live performances. Since there is often no practical way to measure your actual exposure in these circumstances, you must make creative use of the non-linear highlight saturation behavior of your camera. Unfortunately, the AF100 doesn't appear to handle these situations as gracefully we'd hope.
For extreme lighting situations, what I'd really want is a camera sensor that compresses highlights without hard clipping or color shifts. This could probably be done with a Bayer Filter composed mostly of non-filtered clear elements calibrated to directly produce pure luma signals. Less sensitive chroma sensors would be interspersed among the luma sensors in a regular pattern. With high-ND color filters, the chroma sensors would not saturate even with heavy overexposure of the surrounding luma sensors, maintaining accurate color detection even for blown highlights. This type of sensor design could produce a full-color YCC gamut directly, without needing an intermediate RGB conversion stage.
Hunter Starnes
Active member
This is all very informative! Thank you Barry and others for doing all the hard work for the rest of us! 
Barry_Green
Moderator
One last observation on this -- I ran through the other gammas just to see if there was any big difference. I particularly suspected that "high" might offer some benefit, but ... no, all the gammas behave pretty much the same, except -- Cine-V actually lets you push even further. You can go to about 91 IRE before the red channel is maxxed out, and 92 and even 93 still looks to be the same basic color without a shift.
So if you absolutely positively want to push your skintones some 25 IRE into overexposure and have them still "hold", CINE-V gamma looks like the recordholder, with CINE-D a close second. The biggest thing that makes the biggest difference is to drop the chroma level as low as you can, and then the gamma can add just a little bit extra rolloff.
So if you absolutely positively want to push your skintones some 25 IRE into overexposure and have them still "hold", CINE-V gamma looks like the recordholder, with CINE-D a close second. The biggest thing that makes the biggest difference is to drop the chroma level as low as you can, and then the gamma can add just a little bit extra rolloff.