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Explaining Bit Depth...

 
Author desmondqford
ZRO
#1 | Posted: 28 Aug 2012 15:27 
After a failed fashion video shoot with the Canon 7D and 5DMarkIII, in which the client was extremely dissatisfied and rejected the work, the producer and director asked what went wrong and why an Alexa or Epic would be a better choice for color critical work.

The colors recorded didn't match the fabric and in some cases were dramatically off. For example, teal came out navy blue. Navy blue came out black. And all the blacks lost all the details and were murky...

These are fashion people who work exclusively in stills. They're just now branching out and adding short video clips to their website of models walking a runway wearing the specific clothing so that customers can see how it actually looks in motion.

I said that the reason the colors were off was due to the bit depth. The 7D and 5D have a bit depth of 8, whereas the Alexa or Epic have 12 bit depth. Bit depth works exponentially. Thus, 8bits is equal to 256 colors per code value (or color channel such as Red, Green and Blue), whereas 12bits is equal to 4,096 possible colors. Therefore, some of these obscure colors that clothing was made from, wasn't possible in an 8bit camera and if anything would have to be added in post via CGI or some type of motion graphics.

I know that Red and Alexa are superior in other ways too, obviously, but in respect to color accuracy I thought the culprit lay in bit depth. Is that accurate? Is my understanding of bit depth accurate?

Now they want to redo the shoot, but don't want to pay for the Alexa/Red rental. They blame the DP, who all along requested an Epic but was informed two days before the shoot that it wasn't in the budget and that they would use a 7D. Is there any hope for such a demanding client? What's more, they asked me to match the colors of the video to the stills which were shot in Raw on a 5D and then dramatically retouched!

Many thanks for your help!


DF

Author Steve

INF
Male
#2 | Posted: 28 Aug 2012 17:47 
I doubt very much the 8 bit signal is the problem. We have been using 8 bits for years without any such problems.

The number of 'colours' is not the 256 levels you mention, as the colour count of any 8 bit image is in excess of 16 million colours - more than enough for most of the colours we see in the world around us.

The more likely problem is lack of accurate IR filtering for the colour issues, and poor exposure curves for the shadow problem. The in-camera compression will not have helper either, but that tends to show blocking or banding artefacts.

We have a lot of users (Gamma Curve) users doing some fantastic work with DSLR cameras, and the results are often very, very good.
Steve Shaw
Mob Boss at Light Illusion

Author desmondqford
ZRO
#3 | Posted: 28 Aug 2012 18:47 
Thanks for explaining the bit depth question. You make really good sense. I forgot that it's 256x256x256!

This is so complicated then. I own a 5D as well and I often shoot non-professional video on it in natural light. I don't use filters or matte boxes, just EF lenses. I never have color issues like this.

I was on the set, shot on a typical photo cyc, and it was very well lit. The DP had a huge lighting package, Arri etc.... However, the images appear so dark and murky and the colors are very inaccurate. Skin tones are horrible too, both with the 5D and 7D. I tried grading it in Resolve and it falls apart easily even though I was told by many that the codec and compression for the 5D MarkIII is supposed to be a big improvement upon the MarkII...

I really can't see what went wrong? So frustrated.

Author Steve

INF
Male
#4 | Posted: 29 Aug 2012 17:43 
That actually sounds like poor camera set-up to me... but impossible to say without seeing example images.

Were Light Illusion EOS Gamma Curves not used? Or did someone play with the 'Picture Styles' in-camera?

Steve
Steve Shaw
Mob Boss at Light Illusion

Author desmondqford
ZRO
#5 | Posted: 30 Aug 2012 04:23 
No Light Illusion Gamma Curves were used. I'm currently researching them now to see how they will benefit me, which is why I'm on this forum...

The DP set the the picture profile to Standard and adjusted to saturation to -2 and the contrast to -1. Also, he had the aperture at 6.0, ISO 320, Shutter 50 on a EF 24-105 lens, and much of the footage ended up being underexposed since a lot of the clothing was black, navy blue or teal.

Author Jay Friesen
ZRO
#6 | Posted: 1 Sep 2012 13:52 | Edited by: Jay Friesen 
Yeah, my guess is with Steve. Very little do with bit depth and more to do with bad exposures. Add that to all the other inherent issues with DSLRs and you get horrible images I use the gamma curves for everything but things still have to be exposed well.

Display Calibration Light Illusion Forums / Display Calibration /
 Explaining Bit Depth...

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