16 and 32 bit color correction

Thomas Smet · November 1st, 2007, 12:35 AM

Glenn thank you for confirming what I have always found to be true. I agree about the 8 bit yuv part. This is why I usually try to work in 8 bit RGB although with camera footage this gets kind of hard to do.

Bill Ravens · November 1st, 2007, 07:19 AM

Glenn...

Aren't there some other benefits to 10 bit processing that haven't been mentioned? If you work in 10-bit space for CCing, banding is less than when working in 8-bit, regardless of the bit depth of the original file? If output has to go back to 8-bit space, the tradeoff then becomes one of how well the conversion is dithered back to 8-bit.

Or have I missed the point of Thomas' question.

Glenn Chan · November 1st, 2007, 11:46 AM

Er... it depends on what you're talking about??

You need to specify where the 10-bit is occuring. Is it:
A- Converting your 8-bit Y'CbCr footage to a 10-bit intermediate. (There might be different ways of doing this. The simplest way of doing this... padding with 0s... doesn't help you.)
B- What bit depth you're passing from filter to filter.
C- If you render to an intermediate here (e.g. render to new track), what is the bit depth of the intermediate.
D- Output bit depth. e.g. 8-bit R'G'B', 10-bit SDI, etc. etc.

Bill Ravens · November 1st, 2007, 12:29 PM

I'm assuming what I would consider to be the optimised workflow, i.e.:

1-Original m2t file is 8 bit, converted to 10 bit intermediate(like with CFHD)
2-CC in vegas8 with 32 bit float
3-output back to 8 bit space, WMV or short form MPEG2 for SD-DVD distribution.

Thomas Smet · November 1st, 2007, 06:51 PM

I think it only helps if you convert to a 10 bit format first.

For example if you load a 8 bit image into Photoshop and switch the color mode to 16 bit it doesn't help at all. I tried this in After Effects as well. I will have to try a few other programs but I think it pretty much comes down to it takes too much processing which is what a intermediate format does anyway. Since the video is getting converted they can try to blend and smooth the bit depth. At least this is how I think they are doing it. Kind of how if you convert a 24 bit image to a 8 bit image and you can add dithering so you do not see the banding.

As far as I can tell though if you just pop in a 8 bit format and try to work with it in a 10 bit color space you will not really gain anything at all. Unless there is a color tool out there that will up sample the color depth on the fly in RT but I don't think there is.

Glenn Chan · November 1st, 2007, 07:11 PM

??

(I don't understand your last message Thomas.)

Quote:

1-Original m2t file is 8 bit, converted to 10 bit intermediate(like with CFHD)
2-CC in vegas8 with 32 bit float
3-output back to 8 bit space, WMV or short form MPEG2 for SD-DVD distribution.

I don't think step #1 necessarily helps. I haven't tested Cineform carefully though.

As far as outputting goes, you might want to output to a Cineform intermediate (or some other high quality format). From there make all the versions you need. For Vegas, you'll need to pay attention to levels and color space conversions.

Bill Ravens · November 1st, 2007, 08:33 PM

Yeah....
Mostly just my theoretical workflow. I've made the same experiment in Photoshop. Start with an 8 bit image. perform a CC on the image and look at the histogram...banding all over the place as the color gamut gets stretched out. Upgrade the original to 16 bit and do the same CC. Look at the histogram and you'll see the banding is nowhere near as bad. I suppose the upgrading process extrapolates a lot of color data where there wasn't any in the 8 bit image. You NEVER get something for nothing...one of the laws of physics. But, you can minimize the price(penalty) you pay.You guys understand the internal processing better than I do. Why oh why isn't CFHD used as a delivery format? I'd gladly suffer shorter record lengths in exchange for higher quality images. Guess it's the same reason there aren't pro-sumer videocams on the market with CF card media.

Glenn Chan · November 1st, 2007, 08:52 PM

Quote:

Why oh why isn't CFHD used as a delivery format? I'd gladly suffer shorter record lengths in exchange for higher quality images.

For various workflow reasons it might be a bad idea.

A- No RS-422 control. (Until recently.)
Most systems work off RS-422 control + SDI... one of the widely-supported standards in the broadcast industry. And I mean a real standard that works 100%, unlike HDV or MXF.
B- Sending hard drives around can be more expensive, and you don't have that archive solution / shelf life.
C- File format incompatibilities and other software incompatibilities would break the system.
D- No insert editing. (Convenient...) And the "deck" doesn't add timecode burns in real-time, which is useful when you need to make screeners of your master.

Uli Mors · November 6th, 2007, 12:34 AM

I wanted to state that VEGAS now supports 32 Bit calculation (optional, find it under "properties")

ULI

Alessandro Machi · November 23rd, 2007, 11:48 AM

I've used waveforms since the early 90's. I don't believe that the 0 to 100 IRE scale can be correctly configured in a linear fashion when it comes to codec assimilation. So all of these color correction systems are flawed because they mistakenly think that the codecs should be linearly allocated.

Bill Ravens · November 23rd, 2007, 11:56 AM

SMS acknowledges the inaccuracies inherent in a nonlinear gamma by allowing you to select linear gamma or gamma 2.22 with 32 bit floating point math. There are other issues related to using a linear gamma that keep it from being "mainstream" as you suggest.

November 1st, 2007, 11:46 AM	#18
Glenn Chan Inner Circle Join Date: Jun 2003 Location: Toronto, Canada Posts: 4,750	Er... it depends on what you're talking about?? You need to specify where the 10-bit is occuring. Is it: A- Converting your 8-bit Y'CbCr footage to a 10-bit intermediate. (There might be different ways of doing this. The simplest way of doing this... padding with 0s... doesn't help you.) B- What bit depth you're passing from filter to filter. C- If you render to an intermediate here (e.g. render to new track), what is the bit depth of the intermediate. D- Output bit depth. e.g. 8-bit R'G'B', 10-bit SDI, etc. etc. Last edited by Glenn Chan; November 1st, 2007 at 12:33 PM.

November 23rd, 2007, 11:48 AM	#25
Alessandro Machi Major Player Join Date: Oct 2003 Location: Los Angeles, Ca USA Posts: 553	I've used waveforms since the early 90's. I don't believe that the 0 to 100 IRE scale can be correctly configured in a linear fashion when it comes to codec assimilation. So all of these color correction systems are flawed because they mistakenly think that the codecs should be linearly allocated. __________________ https://alexlogic.blogspot.com/ Los Angeles Emmy Winner (yes, used a video edit controller and loved doing so.)

November 1st, 2007, 12:35 AM	#16
Thomas Smet Trustee Join Date: Mar 2004 Location: Milwaukee, WI Posts: 1,719	Glenn thank you for confirming what I have always found to be true. I agree about the 8 bit yuv part. This is why I usually try to work in 8 bit RGB although with camera footage this gets kind of hard to do.

November 1st, 2007, 07:19 AM	#17
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Glenn... Aren't there some other benefits to 10 bit processing that haven't been mentioned? If you work in 10-bit space for CCing, banding is less than when working in 8-bit, regardless of the bit depth of the original file? If output has to go back to 8-bit space, the tradeoff then becomes one of how well the conversion is dithered back to 8-bit. Or have I missed the point of Thomas' question.

November 1st, 2007, 12:29 PM	#19
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	I'm assuming what I would consider to be the optimised workflow, i.e.: 1-Original m2t file is 8 bit, converted to 10 bit intermediate(like with CFHD) 2-CC in vegas8 with 32 bit float 3-output back to 8 bit space, WMV or short form MPEG2 for SD-DVD distribution.

November 1st, 2007, 06:51 PM	#20
Thomas Smet Trustee Join Date: Mar 2004 Location: Milwaukee, WI Posts: 1,719	I think it only helps if you convert to a 10 bit format first. For example if you load a 8 bit image into Photoshop and switch the color mode to 16 bit it doesn't help at all. I tried this in After Effects as well. I will have to try a few other programs but I think it pretty much comes down to it takes too much processing which is what a intermediate format does anyway. Since the video is getting converted they can try to blend and smooth the bit depth. At least this is how I think they are doing it. Kind of how if you convert a 24 bit image to a 8 bit image and you can add dithering so you do not see the banding. As far as I can tell though if you just pop in a 8 bit format and try to work with it in a 10 bit color space you will not really gain anything at all. Unless there is a color tool out there that will up sample the color depth on the fly in RT but I don't think there is.

November 1st, 2007, 08:33 PM	#22
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Yeah.... Mostly just my theoretical workflow. I've made the same experiment in Photoshop. Start with an 8 bit image. perform a CC on the image and look at the histogram...banding all over the place as the color gamut gets stretched out. Upgrade the original to 16 bit and do the same CC. Look at the histogram and you'll see the banding is nowhere near as bad. I suppose the upgrading process extrapolates a lot of color data where there wasn't any in the 8 bit image. You NEVER get something for nothing...one of the laws of physics. But, you can minimize the price(penalty) you pay.You guys understand the internal processing better than I do. Why oh why isn't CFHD used as a delivery format? I'd gladly suffer shorter record lengths in exchange for higher quality images. Guess it's the same reason there aren't pro-sumer videocams on the market with CF card media.

November 6th, 2007, 12:34 AM	#24
Uli Mors Major Player Join Date: May 2006 Location: Germany Posts: 565	I wanted to state that VEGAS now supports 32 Bit calculation (optional, find it under "properties") ULI

November 23rd, 2007, 11:56 AM	#26
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	SMS acknowledges the inaccuracies inherent in a nonlinear gamma by allowing you to select linear gamma or gamma 2.22 with 32 bit floating point math. There are other issues related to using a linear gamma that keep it from being "mainstream" as you suggest.