abrupt highlights clipping

[Jamie Baughman]

Just to jump in to the conversation...

Here's a grab of a test shoot I did yesterday.

I'm a little dark inside (the mantle) and totally blown out...especially in the window picture right.

I could have sworn the stuff I've shot with my XL-2 (my old cam) wouldn't have been so drastic...but this is a totally different camera. There are a lot more examples where there are these drastic brightness conditions, but also a lot of stuff that just blew me away with how stunning it was...and this was shooting 720p.

I love the camera so far, just think it will take some time for us to get to know each other!

I'm chalking this up to operator error since it was my first day out with the camera in a practical situation and wasn't equipped with filters.

[Steven Thomas]

After having read Bob's post, Piotr, I know you were using Bill's original TC setting which uses a standard gamma. Did you happen to try turning off the profiles and use the camera's default standard video settings?

That would of been interesting. Bill, I know you took great care in setting up the color channels. Maybe its possible that things are a bit hot with these setting which may drive the colors to clipping a bit early, which may be causing what Piotr has been concentrating on. But on the otherhand, it sounds like you did a decent job setting these up.

Bob, which image did you grab the blue channel histo from? I know he had a couple examples of intentionally over exposed to show what he is seeing.

[Steven Thomas]

Jamie,
As you said it was over exposed. Also, I'm not sure what you were focusing on?

[Steven Thomas]

To add to Bob's post, Adam Wilt's latest EX1 review he mentioned the following quote regarding EX1 highlights:

"I’ve found that the EX1’s knee does a fine job except when highlights are strongly colored. Saturated highlights show more hue shift and harsh clipping than I’d like. I’m exploring this further out of curiosity, but even if the knees were perfect I would still shoot with cine gammas, because I prefer the progressive compression to the look of a traditional knee."

[Bob Grant]

Originally Posted by Steven Thomas

After having read Bob's post, Piotr, I know you were using Bill's original TC setting which uses a standard gamma. Did you happen to try turning off the profiles and use the camera's default standard video settings?

That would of been interesting. Bill, I know you took great care in setting up the color channels. Maybe its possible that things are a bit hot with these setting which may drive the colors to clipping a bit early, which may be causing what Piotr has been concentrating on. But on the otherhand, it sounds like you did a decent job setting these up.

Bob, which image did you grab the blue channel histo from? I know he had a couple examples of intentionally over exposed to show what he is seeing.

The one from here http://www.dvinfo.net/conf/showpost....5&postcount=53

I incorrectly named my screen grab Image41, it's actually from image42!

The green channel looks pretty much the same, the red channel isn't clipped.
This is always the problem with cameras that go to 11, if you have anything other than a specular highlight then having any channel go into clipping wierd things will happen if you're not very careful. Even WB setting can affect the color shift as you go into clipping. Trying to fix these problems in post varies from extremely difficult to impossible. Shooting it right is the answer. If that scene was being shot on film there'd be serious lighting in use and the DP running around with a light meter. Sony gave us a cheap camera that gets us one notch closer to film. We need to learn what DPs have been doing for nearly a century.

Probably what the EX1 should have is false color metering but that could be difficult to implement and again you need to know what it's telling you.

[Leonard Levy]

What do you mean by the camera goes to 11?

[Christopher Barry]

Some funky skies have also been seen in footage comparing the EX1 to the HVX. If I recall, default STD curve used. I can not find the link, so I frame grabbed a problem shot.
http://www.siliconcine.net/temp/Blew_Skies.jpg
White balance also looks too blue, a point Bill raised earlier for consideration. My gut feeling is the STD curve and perhaps the knee is the cause, coupled with exposure.

I posted this before in another thread:
From the XDCam HD brochure (the 350 series), we can see how different the Standard curve compares to the Cine curves, and a lot more of your highlights would have shown a burnt out look with "Standard" curve.
http://www.siliconcine.net/temp/XDCAM_Gamna_Curves.jpg

The Cine Gamma Curves for the EX1, from the brochure and manual.
http://www.siliconcine.net/temp/EX1_Gamma_Curves.jpg

[Steven Thomas]

Yes I saw this comparison too and also remember this being brought up.

There's no doubt that the image is way cool. It should of been white balanced. I believe the standard gamma was used. I also agree that the image is over exposed.
This may be just how the standard gamma blows out its highlights when over exposed. I have never seen this since I live on the cine curves.

We'll have to perform some experiments.

BTW, I have this same comparison, but it is 1080P version (Not the 720P version). The EX1 in the same shot does not show this problem. I'm not sure if they just did a better job with exposure, or they switched on a cine curve.

[Bob Grant]

Originally Posted by Leonard Levy

What do you mean by the camera goes to 11?

It can record right upto hard digital clipping at 110%. Some NLEs will clip that at 100% unless told otherwise.

[Bill Ravens]

Very interesting, Chris. When I looked at the b&w step wedges with the WFM, I compared STD with Cine gamma curves; and, initially chose STD for TC1 because it exhibited a more (vertically) symetrical wfm pattern, as I would expect with the STD curve you show in the F350 series curves. Overexposure indicated a definite cutoff at 100%. I, subsequently, changed to the CINE gamma curve for TC2 because of the more gentle rolloff characteristics at the right end. Furthermore, Adam Wilt writes the following about the CINE2 preset:
"• CINE2 – “broadcast safe cine”. CINE1 rescaled with whites limited to 100%."

If I get a chance, tomorrow, I'll post a screen capture of the WFM displays for the STD vs Cine Gamma curves.

[Christopher Barry]

Steven, I also observed the 1080p footage did not have the same funky sky as the 720p. Information from that comparison was perhaps not clearly documented and published.

I hope the following info is not too OT from Piotr's initial post and request for answers to this issue, however, it may have some general relevance and may assist those interested in comparing STD and CINE gamma curves:

It has been documented that even the F900's Standard gamma curve suffers in shots requiring a wide dynamic range. Have a look at this Standard curve image and the Digital Praxis custom gamma curve graphs applied to the camera/scene thereafter. Steve Shaw has been generous to provide a lot of information on the Digital Praxis site.
http://www.digitalpraxis.net/sonycurves.htm

You can see that the Digital Praxis custom gamma curves for the F900 blast the F900's Standard curve, compressing the range, lifting the blacks, preserving the highlights, and very nicely done by DoP, Geoff Boyle. Some curves are good for record, edit and finish with no grading (REC709 preset), others require post grading, however, there is more detail in the image and the right S shaped curves filter applied in post will extract the most out of the image (Bill Raven's "art"). The caveat I would add is that the EX1 codec, even in HQ mode, may have limitations to exploit such extreme PP settings that one may try to dial into the EX1 menus, such as trying to emulating the Cineon Log curve, due to the codec's 8-bit depth and compression likely not being robust enough to correct such extreme grading in post. In that case, recording via HD-SDI to an uncompressed 10-bit 4:2:2 device may be the next step for some. Thanks to Bob Grant for putting some of this into perspective for me, with his experience with the SI-2K camera and edit suite based on the CineForm codec.

Bill, your Wfm screen captures and explanation would be much appreciated, in this quest for knowledge and exploiting the EX1's goodness, to find it's limit!

[Piotr Wozniacki]

Originally Posted by Steven Thomas

After having read Bob's post, Piotr, I know you were using Bill's original TC setting which uses a standard gamma. Did you happen to try turning off the profiles and use the camera's default standard video settings?

Steven, thanks for joining the discussion. Let me address a couple of things:

1. Some of my grabs were intentionally overexposed to show conditions where ALL sky goes white. Yes I was checking with Vegas Histogram, Waveform and RGB Parade scopes and confirm that even the image41 shows levels upd to 110% (for Green and Blue). And yet it's the image41' exposure that one would use to "balance" between slightly overexposing the sky and showing details in the foreground - the camera' histogram looked normal to me, and nothing else spelled the disaster, either (all looked OK apart from the WB, but that has already been said).

2. To address Steven's question above: yes, I did try the same scenery with STD3 but Bill's PP off (i.e.default factory setting); the camera behaved in the very same way (auto-exposure, zebra and histogram - wise), BUT the image I got was fine in that I could properly expose the foreground (the sky went all white then), or keep the sky colour (with the foregroud a bit dark, but watchable).

3. As I mentioned many times before, it is the combination of Bill PP's modified Hisat matrix with the standard STD3 gamma that is a no-no. Why? Well, suppose one is already aware of what may happen to partially blow-out sky; he may either expose for the sky (to keep it safe and show the clouds etc), or for the darker foregorund (e.g. to show the face of a person standing there). Unfortunately, with this PP/STD3 combination, one must go way down with the exposure (much lower than the histogram/zebra would suggest) to avoid the patchy sky like I showed - so much so that the foregrund becomes already way too dark, and - due to the PP high colour saturation levels - oversaturated and noisy (see image38).

So, that the sky is clipping doesn't surprize me, as I wanted to avoid underexposed and noisy foreground. If the way it doesn't clip behind the trees is normal for a camera of this (high) class, as Bob is suggesting - is fine with me, as well. However - and I have said it before, as well - using high-saturation PP with STD3 curve is dangerous in that the zebra/histofram and autoexposure of the camera offer no help in getting the right balance (if it possible at all).

Thanks everyone for their participation.

[Piotr Wozniacki]

Originally Posted by Jamie Baughman

I'm a little dark inside (the mantle) and totally blown out...especially in the window picture right.

I could have sworn the stuff I've shot with my XL-2 (my old cam) wouldn't have been so drastic...but this is a totally different camera.

Jamie,

I guess what you're showing with your picture is normal, though can see some traces of the strange abrupt blow-out beginning. I don't know your setting used with the picture you posted, it would be good if you remembered!

For comparison's sake, here go couple more examples of mine (sorry for the WB and focus being off; I took them while walking):

The first two are also through-the-window looks like yours; all factory settings used (i.e. STD3, but no PP at all). I don't think the outside is too much overblown.

The bottom two is the "horror continued" - the first pictures recorded while walking outside through the door (with Auto-Iris on), right after having dialed in Bill's TrueColour PP (SDT3 with Hisat matrix); note that even though I changed the WB quickly (to another bad value, but that proves to be of no importance), those trees against the sky look almost as if there was hoar frost on them!

Go figure...

EDIT: An idea occured to me and I went outside to check immediately - and yes, one can actually see the artefacts behind the trees in the camera's LCD! It's enough to switch peaking off (when I recorded these tests, I had it on with high intensity; since I was on autofocus the trees were all red with peaking, which obscured what was happening with the clipping around them...Now at least I know it's possible to observe and avoid this while shooting.

[Piotr Wozniacki]

Originally Posted by Bill Ravens

If I get a chance, tomorrow, I'll post a screen capture of the WFM displays for the STD vs Cine Gamma curves.

Please do, Bill! I've been searching for some graphical comparison of the STD curves with Cine gammas (the latter are depicted in the EX1 pdf brochure), but couldn't find anything.

[Piotr Wozniacki]

Have some bad news for you guys - even without Bill's TrueColour PP, with the standard gamma curve (STD3, all factory setting) the ugly phenomenon when at the verge of sky clipping is still there :(

And, which is even stranger, it's bluish NOT because of the blue sky in the background; today I got it again with the sky totally overcast (light gray).

Evidently malfunctioning Knee/highlight processing, or at least totally not idiot-proof - even with the out-of-the-box settings!

Again, please try to reproduce it with your units, cause - after being somewhat reassured with the discussion in this thread - I'm again suspecting my camera IS malfunctioning, after all.

PS: Bill, I'm taking back my statements that your TC PP is a "no-no" with STD3 - if anything, it can only make the phenomenon even uglier by making the artefacts more saturated...