>100 ire

D

djhg

Member
I am wondering if it's wise to exploit the entire luminosity
gamut of the FS100. Seems like a no-brainer -- of course
so, and then squeeze it down in post to broadcast safe
(or wherever is required.)

I didnt expect this to come up at all, because I didn't
think cameras were designed to resolve above 100.
But the FS100 appears to differentiate tones up to
about 115. The question arises because my pro camera
store sales people advise never to rely on holding any
detail above 100 even if the camera can see it..
But it seems to me if the detail's still there in the video when
I view it in post (it is) it would be a waste of latitude
not to use it to see the full dynamic range of the camera.
 
Bad things happen at high brightness levels. Primarily, color shifts and the dreaded "chroma clipping" and yellow skin highlights and such.
 
depends... what is the post chain? can it keep full range intact? Do you have control of the post workflow -or- hand off to clients?

i disagree with Barry, nothing bad happens above 100 and below 109 IRE - unless you are using software that clips, and in that case the problem is with pro-sumer software

Avid Media Composer, Lightworks, Smoke, Resolve & FCX all maintain full range

PP and FCP do not

I do have control of the post chain, and i use full range in camera, and Avid in post.... all good!
 
There was a lot of reasons not to use whites over 100 back in the analog CRT days. I've seen white levels over 100 actually causing monitors to make audible whining noises while the picture would bloom and vertical lines would get bowed. It was a mess! Digital devices are less prone to this, if at all, but I'm not convinced that you're really going to get too much extra detail from allowing the superwhite levels.
 
Dermot said:
i disagree with Barry, nothing bad happens above 100 and below 109 IRE - unless you are using software that clips, and in that case the problem is with pro-sumer software
Click to expand...
I'm not talking about post, I'm talking about in-camera. At high brightness levels the odds increase that one or more of the color channels is clipping, and that causes either color skewing or highlight desaturation.

If you're talking about shooting all-white or shades of gray, then it may not be an issue. Try overexposing skin up to 90-100 IRE and see what happens -- it'll turn sickly yellow, because the red channel clips first, long long before you get to 100+ IRE.
 
Barry_Green said:
I'm not talking about post, I'm talking about in-camera. At high brightness levels the odds increase that one or more of the color channels is clipping, and that causes either color skewing or highlight desaturation.

If you're talking about shooting all-white or shades of gray, then it may not be an issue. Try overexposing skin up to 90-100 IRE and see what happens -- it'll turn sickly yellow, because the red channel clips first, long long before you get to 100+ IRE.
Click to expand...

If it's clipping in camera then it's over 109.... any color channel / any time.. so keep it under 109 - simple no?

and no, the red channel does not clip long before the others on my cameras.... you might want to take long hard look at your choice of profiles.... seems like there's a chance something is suboptimal in that department

as to over 100 IRE causeing issues at delivery? Oh yea, well known, instant QC fail & clamped at the broadcasters output anyway.... also an issue is most Qt codec's are looking for video legal on input, so sending them over level can easy resualt in your Qt not looking like what you thought you had... Ok, one of a thousand reason why a Qt can look crap

Shoot full range, grade in post, be happy, don't worry about "issues" over 100 unless your post chain can't accomadate -or- you have no control of the post chain

works for me

d
 
Andrius Simutis said:
There was a lot of reasons not to use whites over 100 back in the analog CRT days. I've seen white levels over 100 actually causing monitors to make audible whining noises while the picture would bloom and vertical lines would get bowed. It was a mess! Digital devices are less prone to this, if at all, but I'm not convinced that you're really going to get too much extra detail from allowing the superwhite levels.
Click to expand...

At least as far as what a properly calibrated display will show, 100 IRE= 700mv analog CRT reference voltage= max REC709 8 bit white value of 235 or 10-bit value of 940= 100% white with no detail. There is no whiter than white. If you are working in or calibrated to a different color space gamma, you may see something different, but that just means the scope values are off for the color space and monitor calibration, not that you are getting more usable image data.

Barry is right, if you want better highlight rendering without clipping artifacts, the better practice is to under expose slightly rather than push the limits.
 
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Dermot said:
If it's clipping in camera then it's over 109.... any color channel / any time.. so keep it under 109 - simple no?
Click to expand...
Simple, yes, but completely incorrect.

IRE is not a reflection of any one color channel, it's the composite of all the color channels together. The formula in HD (rec 709) is about 21% red, 72% green, and 7% blue. In standard-def it was more like 60% green, 29% red, 11% blue.



and no, the red channel does not clip long before the others on my cameras....
Click to expand...
Of course it does, when shooting something red... the red will max out long before the IRE reaches 109.

Take an example of red 255, green 128, blue 128. What would be the IRE that your waveform or zebras would display? About 60 IRE. But the red channel is already clipped at that point.

Feed your camera's output to a waveform monitor where you can separate out the color channels and you'll see what's happening. Point it at a greenscreen and light the green to 100% full saturation, and you'll see that your IRE is reading (again) about 60. Then try it with blue -- you'll see that the IRE level is down around 10, but the blue channel is 100% fully saturated and already clipping.
 
TO add to Barry's point (which doesn't need me to verify as accurate), when you're doing any form of colour timing or grade you should be using the RGB overlay waveform IMO. And if you are / do in the future - you will see Barry's point clearly illustrated.
 
Just realized there's an easier way to demonstrate it. Make a solid color in your NLE (255/128/128) and you'll see that your waveform displays it as about 69 IRE. It's a pinkish salmon, and the waveform shows 69 IRE, but you know the red channel is 100% maxxed out. Make it brighter -- what happens? The blue and green go up on the waveform, the IRE goes up, but the red can't go any higher -- it's already clipped -- and so the result is the color starts to get all washed out.

Next, make a solid color of rgb 0/255/0. That's 100% green, the green channel fully maxxed out. What IRE do you expect it will show? In mine, it shows right on about 61. The rgb parade shows green at 100% saturation, but the IRE is 61. Sure I could make it "brighter" but the net result will be just to make it a paler green. Once you're clipped (at 255) you're clipped, it can't get any brighter than that. This is also another reason why most digital imaging techs will tell you that when shooting greenscreen, keep the greenscreen area at no more than 60 IRE. It's already at full brightness at that point; any brighter will just pollute the color.
 
Barry_Green said:
I'm not talking about post, I'm talking about in-camera. At high brightness levels the odds increase that one or more of the color channels is clipping, and that causes either color skewing or highlight desaturation.

If you're talking about shooting all-white or shades of gray, then it may not be an issue. Try overexposing skin up to 90-100 IRE and see what happens -- it'll turn sickly yellow, because the red channel clips first, long long before you get to 100+ IRE.
Click to expand...

Barry_Green said:
Simple, yes, but completely incorrect.

IRE is not a reflection of any one color channel, it's the composite of all the color channels together. The formula in HD (rec 709) is about 21% red, 72% green, and 7% blue. In standard-def it was more like 60% green, 29% red, 11% blue.




Of course it does, when shooting something red... the red will max out long before the IRE reaches 109.

Take an example of red 255, green 128, blue 128. What would be the IRE that your waveform or zebras would display? About 60 IRE. But the red channel is already clipped at that point.

Feed your camera's output to a waveform monitor where you can separate out the color channels and you'll see what's happening. Point it at a greenscreen and light the green to 100% full saturation, and you'll see that your IRE is reading (again) about 60. Then try it with blue -- you'll see that the IRE level is down around 10, but the blue channel is 100% fully saturated and already clipping.
Click to expand...

i think you might be danceing on the head of a pin...

yea i have RGB parade, luma and composite on my scopes... so yea, i could shoot a green/blue/red anything and see 40ire on color channel + Luma and see composite at well past 120...

but that's not a reason to limit your range in shooting to under 100IRE one way or the other...

I shoot from -15 to 109, and i don't have issues with clipping cause i stay over -15 / under 109.

So guess if you can't be comfortable you are monitoring and exposeing optimaly, you can't be sure of the post chain.. then yea... kneecap the camera...

you want the best out of it ? shoot full range and avoid the fauxlog crapola.... release the chains that shackle ;-)

d
 
Dermot said:
i think you might be danceing on the head of a pin...

yea i have RGB parade, luma and composite on my scopes... so yea, i could shoot a green/blue/red anything and see 40ire on color channel + Luma and see composite at well past 120...

but that's not a reason to limit your range in shooting to under 100IRE one way or the other...

I shoot from -15 to 109, and i don't have issues with clipping cause i stay over -15 / under 109.

So guess if you can't be comfortable you are monitoring and exposeing optimaly, you can't be sure of the post chain.. then yea... kneecap the camera...

you want the best out of it ? shoot full range and avoid the fauxlog crapola.... release the chains that shackle ;-)

d
Click to expand...

Actually I do agree with this. These cameras are potentially capable of capturing DR well beyond the defined limits of HD video codecs and I am not a fan of the current fad log curves as the best possible means of taking advantage of that. If you know your camera intimately enough to be confident of your results at the extremes with whatever settings you prefer, I say go for it. Those buffer zones outside the 0-100 reference range are there to accommodate chroma overshoot. Use them to the max. :Drogar-SunGlass(DBG
 
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