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Old February 14th, 2008, 07:41 PM   #1
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Bringing Up Blacks From Black Clipping???

I'm finding this issue a little difficult to describe so let me first give the facts of the shoot. It was a very bright high contrast scene. Bright white clouds, white cars, black tarmac, shadows in door way and close-up bushes in full shadow. I exposed about half a stop below clipping so have full detail in the clouds. I get same result as described here for all CINE gammas in default settings and in all sorts of scenes.

As shot the darkest part, the bushes show minimal detail as you would expect and I'm trying to bring out a little of this detail with the Color Curves but here is the problem. The strong blacks cut-off sharply just like they clipped. IE the left side of the histogram has a very high value at 0 (zero luminance) and the drops to nothing. The Waveform monitor has a thick line running all along the 0 bar. Trying to drop the end by the lowest blacks even with very fine adjustment seems to drop all the blacks, not just the very bottom, and produces a lot of noise.

What is happening here and why is the EX1 histogram in bright contrasty scene not like a bell curve that tapers at both ends but like a rectangle where blacks (and to some extent white) drop off like the side of a cliff? With HDV I never saw anything like this as I always had gradual drop-off at each end of the luminance scale. I'm really confused as to just what the camera is recording and to how Vegas seems it.
COULD this be due to under-exposing. The picture quality unprocessed is superb, I just want to soften contrast to be more film like.
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Old February 14th, 2008, 08:09 PM   #2
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There are a lot of pixels in the black region of the image and that is what the histogram shows; namely how many pixels are at each brightness. The camera histogram puts black a bit to the right of the apparent zero and in an underexposed image you get that cliff at the black end because that's where all the pixels are. If you over expose it becomes a gradual decline because there aren't many pixels that are dark.
In Photoshop your posted image gives the usual histogram I'd expect (there are a lot of blacks present and no cut-off -- apart from a number down at 0) and the amount of detail in the dark hedge is quite surprising (considering the brightness range in the subject). You can bring it up with levels, but that doesn't help the rest of the image. I would use masking to bring up only the hedge using levels, but noise will be a problem with such an underexposed area.
Looks pretty good, to me.
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Old February 14th, 2008, 08:29 PM   #3
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Thanks Serena. Isn't the exposure latitude of this camera amazing!
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Old February 15th, 2008, 08:13 AM   #4
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Hi Michael,

What did the left side of the EX1 histogram look like when shooting? Was it registering any "0" pixels. How were you guaging white clipping? If zebras, at what setting?

This grab looks very saturated for stock settings. Was that something you did in post? If so, could you post an unaltered out of camera shot?

Very interesting thread!
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Old February 15th, 2008, 04:57 PM   #5
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Hi Michael,

What did the left side of the EX1 histogram look like when shooting? Was it registering any "0" pixels. How were you guaging white clipping? If zebras, at what setting?

This grab looks very saturated for stock settings. Was that something you did in post? If so, could you post an unaltered out of camera shot?

Very interesting thread!
NO POST - .mxf straight from camera. Frame grab from Vegas 8 32-bit time-line.

Matrix was set to HiSAT. Otherwise straight CINE4 with black master -3 and black gamma -2. 1080x 24p

The EX1 histogram was NOT vertical immediate cut-off like I saw in Vegas.

Zebra set at 95 with zebras just gone. That's why I say it is a little underexposed.
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Old February 15th, 2008, 06:27 PM   #6
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Yes, the under exposure is clear in the Photoshop histogram. Working to the 109% limit offers better dynamic range. Or, if you like, less noise in darks. Apply "levels" in post.
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Old February 15th, 2008, 09:45 PM   #7
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Zebra set at 95 with zebras just gone. That's why I say it is a little underexposed.
Thanks for the extra info. If I understand correctly, Zebra set to 95 will start to register Zebra indications at 90. If you backed it off even more from there to be safe, that is likely the issue.

Not sure why the difference in the two histograms.
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Old February 16th, 2008, 03:12 AM   #8
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If I understand correctly, Zebra set to 95 will start to register Zebra indications at 90.
This is the disadvantage of using Zebra 1 only - it show a range rather then above threshold values, which may be confusing. Pity that Zebra 2 is not adjustable, but still I prefer using it alone - at least I know that "just gone" means I'm around 100 IRE.

Zebra 1 is excellent for checking e.g. human faces and alike, within the allowable max range.
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Old February 16th, 2008, 08:50 AM   #9
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This is the disadvantage of using Zebra 1 only - it show a range rather then above threshold values, which may be confusing. Pity that Zebra 2 is not adjustable, but still I prefer using it alone - at least I know that "just gone" means I'm around 100 IRE.
My understanding is that zebra 2 also shows a range (95-105). Is that incorrect?
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Old February 16th, 2008, 09:14 AM   #10
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According to the (Euro) manual, page 40:

2 (Zebra 2): to display a zebra pattern for the video level over 100%.
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Old February 16th, 2008, 09:49 AM   #11
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Thanks Piotr,
I hadn't caught that. That is very helpful.

For Zebra 1, the manual is stating "To display a zebra patttern in the area of +/- 10% centering the video level set with Zebra 1 Level". This reads to me like if Michael had set to 95% that he would start seeing Zebra indications at 85%. Some had said before that it was a 10% range (5% up, 5% down), but this reads to me like 20%.
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Old February 16th, 2008, 10:10 AM   #12
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I think my 95 equates to 90-100 which in reality, when using it at the top end is 90. I realize now that Zebra 1 is meant for a RANGE in the lower areas as for skin and hence the default of 70. For clipping I now believe i was doing it wrong and must use the Zebra 2 set at 100. Today I will repeat my tests using Zebra 2.
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Old February 16th, 2008, 05:45 PM   #13
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You have zebras and you have the histogram, the latter being far more useful.
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Old February 16th, 2008, 08:22 PM   #14
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You have zebras and you have the histogram, the latter being far more useful.
Serena; Did you read my latest post Zebra107= etc ... because if you really find the histogram good maybe my camera has a problem? As I said in that post MY histogram seems useless (except by re calibration) in that when I reach white clipping at 107 my histogram still has three more vertical bars to go! Tell me how your histogram is and how you use it so I can figure if I have a problem but I have never seen a histogram that looks like this one. My white clip, the spot meter says 100 and the Zebras say 107 and my histogram is only at about 80% max?
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Old February 16th, 2008, 08:37 PM   #15
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Regardless of how far to the right the histogram goes surely it's self evident when you hit clipping?
Start by underexposing and open the iris, the more of the graph that disappears to the right of the graph the more you are clipping. Same goes for clipping at the blacks. Remember that a completely black or completely white frame only shows as a single, thin vertical line on a histogram. Keep in mind that a histogram is a statistical plot of the population of pixel values and the old saying about statistics applies unless you take some care in how you read the results.
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