Redlog - still no answer?

[Irri]

I'm going to a grade on Monday and I'm a bit worried.

I spoke to the colourist and he said "I hope you send the nice stuff, not the stuff that some people send which is all milky with blacks up at 40"
I knew exactly what he meant. He wants REC709 or Redspace because he doesn't want to have to grade redlog back to REC709 before he starts grading. I don't expect him to understand this; it's not really his job.

So what do I send him?
REC709 DXP and lose a lot of information?
redlog DPX and have him grading for hours?
REC709 tiffs and have him barely able to use his machine?

I read about a DP who went to a grade and they asked for REC709 DPX. He spent 5 hours unable to get good skin tones and they eventually went to redlog and got the results they wanted.

Unless I've got this completely wrong, redlog is transfer system to disgard and abundance of highlight information in order to retain detail in the lower registers when going to a lower bit depth. But surely it is meant to be used with a some kind of LUT. Does it even need a LUT, isn't it just an equation rather than mappings of individual values? The only thing I have seen about redlog is on Stu's prolost site which gives gamma values for converting to linear light in compositing applications.

We're going to be using a DaVinci. Has anyone found a solution to this problem?

 

[mikeburton]

I'm going to a grade on Monday and I'm a bit worried.

I spoke to the colourist and he said "I hope you send the nice stuff, not the stuff that some people send which is all milky with blacks up at 40"
I knew exactly what he meant. He wants REC709 or Redspace because he doesn't want to have to grade redlog back to REC709 before he starts grading. I don't expect him to understand this; it's not really his job.

So what do I send him?
REC709 DXP and lose a lot of information?
redlog DPX and have him grading for hours?
REC709 tiffs and have him barely able to use his machine?

I read about a DP who went to a grade and they asked for REC709 DPX. He spent 5 hours unable to get good skin tones and they eventually went to redlog and got the results they wanted.

Unless I've got this completely wrong, redlog is transfer system to disgard and abundance of highlight information in order to retain detail in the lower registers when going to a lower bit depth. But surely it is meant to be used with a some kind of LUT. Does it even need a LUT, isn't it just an equation rather than mappings of individual values? The only thing I have seen about redlog is on Stu's prolost site which gives gamma values for converting to linear light in compositing applications.

We're going to be using a DaVinci. Has anyone found a solution to this problem?

I always supply REDLOG to the colorist. Usually, I apply a simple curve in REDCINE without crushing the blacks but enough to make the image less "Milky". This will be the simple one light LUT applied to the DPX's so the colorist still has all the information necessary to make a nice grade and apply the final look but doesn't have to start from scratch and waste time = money. If he is going to master in HDCAM you could supply REC709 but I don't like the gamma curve applied to a REC709 DPX image as much and feel REDLOG is a better overall base to start with.
Also, if he continues to bitch remind him how much he is charging you per hour....

 

[Irri]

Thanks for the reply Mike. That's an interesting idea which I hadn't thought of. One thing though... If I use a curve to make my redlog DPX look like REC709 in RedCine, haven't I just undone the redlog curve?

 

[mikeburton]

Technically you will be undoing the REDLOG Curve, however, the curve I apply will not look like the REC709. It is a customized LUT that I will taylor for each clip or scene. The key is to watch your histogram and not clip highlights or crush the blacks, this way you still leave that decision in your colorist/DP's lap.

 

[M Most]

I spoke to the colourist and he said "I hope you send the nice stuff, not the stuff that some people send which is all milky with blacks up at 40"
I knew exactly what he meant. He wants REC709 or Redspace because he doesn't want to have to grade redlog back to REC709 before he starts grading. I don't expect him to understand this; it's not really his job.
....I read about a DP who went to a grade and they asked for REC709 DPX. He spent 5 hours unable to get good skin tones and they eventually went to redlog and got the results they wanted.

Unless I've got this completely wrong, redlog is transfer system to disgard and abundance of highlight information in order to retain detail in the lower registers when going to a lower bit depth. But surely it is meant to be used with a some kind of LUT. Does it even need a LUT, isn't it just an equation rather than mappings of individual values? The only thing I have seen about redlog is on Stu's prolost site which gives gamma values for converting to linear light in compositing applications.

We're going to be using a DaVinci. Has anyone found a solution to this problem?

Anyone who attempts to use a color corrector, DaVinci or otherwise, on log coded material (Redlog or otherwise) without a log to lin transformation in the processing chain doesn't understand what they're dealing with and will never achieve a proper result. Log coding is used as a container to pack more relevant information in a smaller space based on the general distribution of visual information in an image. It is not meant to be viewed directly and it is not meant to be color corrected directly. It requires an inverse log transformation in order to yield a proper image. This is usually done in DI work by applying a viewing LUT at the end of the processing chain, thus allowing the larger amount of useful information in the log coded image to be manipulated, but a proper, converted image to be viewed. Without an inverse log transformation, the values in the image will never represent a "normal" greyscale. The sad part of all of this is that many video colorists - i.e., "DaVinci guys" - don't know or understand any of it and make comments like the one you quoted. Those that have participated in digital intermediate work do understand it and set up their systems accordingly.

In the case of Redlog, the conversion used by Red is a bit nonstandard, so the inverse LUT applied should account for that. One approach is to set the black point to about 150 (not the "normal" 95), the white point to 1023 (matching Red's original conversion) and negative gamma to somewhere around 1.0 (rather than the "normal" negative gamma of .6 used in Cineon transformations), keeping the display gamma at 1 (Note that these numbers are for using a linlog node in Shake, if you're using After Effects, you want to use a gamma of about 2.7 in the Cineon converter). This shifts the resulting histogram a bit lower on the scale and adds a bit of contrast, allowing for a somewhat more representative starting point if applied as a view LUT at the end of the processing chain. But the important point to keep in mind is that the log curve must be linearized for proper display.

 

[Shawn Booth]

I'm going to a grade on Monday and I'm a bit worried.
I spoke to the colourist and he said "I hope you send the nice stuff, not the stuff that some people send which is all milky with blacks up at 40"
I knew exactly what he meant. He wants REC709 or Redspace because he doesn't want to have to grade redlog back to REC709 before he starts grading. I don't expect him to understand this; it's not really his job.

If you can, find a new colorist. This one's attitude is off.

 

[Irri]

Thanks for the replies.

The colourist wasn't being nasty, he just found it easier to grade. He may not understand the idea of the log conversion, but I do and I still don't know what to do when the files get to the DaVinci. Can you use custom black points, white points and gamma curves on them?

So we are still in the same place? Zero information from RED about the file format, a few gamma curves for converting to linear in compositing applications, and no way to send our clips in high quality to a any post house that doesn't have Scratch.

 

[ericyoung]

Thanks for the replies.
...So we are still in the same place? Zero information from RED about the file format, a few gamma curves for converting to linear in compositing applications, and no way to send our clips in high quality to a any post house that doesn't have Scratch.

Irri. Try PMs to Stuart English and Graeme Nattress as a heads up about your problem, but please ask them to answer in this thread for everyone's benefit!

 

[Irri]

Oh, I didn't realise you could PM people red names. I'll try GN.

 

[M Most]

Thanks for the replies.

The colourist wasn't being nasty, he just found it easier to grade. He may not understand the idea of the log conversion, but I do and I still don't know what to do when the files get to the DaVinci. Can you use custom black points, white points and gamma curves on them?

The DaVinci 2K is a video device. It is designed to take video formats in, and spit video formats out. It can operate in a data mode - in which you do have access to an output LUT - but in order to do that, you must have the data option, and you must have an external device that can serve up the data files as a continuous sequence, like a tape transport (One device often used for this is a DVS Clipster). In other words, it's designed as a real time processing device for very specific formats. And if you don't have it set up as a data device, those formats are SD and HD video - which is the way it is set up in essentially every post facility that uses it. Just because it's a great color corrector - and it is - doesn't make it an appropriate device if the source material is not video. That's why DaVinci also makes Resolve, which IS a data driven device, and has the appropriate architecture for that type of work. You can, of course, use an external "LUT box", such as a LUTher or a Truelight box, as well as some others - to apply an output LUT in real time that can feed both the monitor and the recorder. You could also use something like a Cinetal monitor with a built in display LUT as a pass through. But most video facilities are not equipped to do that.

Your post, and this thread, illustrates very well some of the points other threads are also touching on - the growing pains of trying to apply existing post methods and equipment to new formats that don't fit into that path. The immediacy of video and video post production, the ability to instantly play back at its best quality and manipulate those images, has created expectations on the part of many in and out of the mainstream post industry that high resolution file based methods cannot currently match. That's neither good or bad, it just is. The lesson to be learned (and it still in the process of being learned) is that when new formats come along, new approaches need to be taken, and new time frames must be realistically arrived at, so that the expectations can be fulfilled sensibly.

 

[Irri]

Thanks for the comprehensive information about the DaVinci. I guess there isn't much I can do before the grade and it's really not my problem.

I see what you mean about existing post methods, but I don't see why I can't just add a LUT to Apple Color, and grade my 10 bit redlog DPX sequence.

 

[M Most]

I see what you mean about existing post methods, but I don't see why I can't just add a LUT to Apple Color, and grade my 10 bit redlog DPX sequence.

You can, if that's what you want to do, are capable of doing, and have the proper monitoring to do correctly and effectively for whatever it is you're delivering.

 

[Irri]

I was meaning in the sense of "Why can't one have a LUT for these applications"

I do have broadcast monitors, but I would prefer to send projects to an experienced colourist. It just seems crazy sitting in the post house watching the guy grading redspace without a LUT.

There is a company that will make LUTs for you, but they charge about 400 pounds and I don't see why we should be paying for that when it is really something the post houses should be looking into.

 

[M Most]

I was meaning in the sense of "Why can't one have a LUT for these applications"

I do have broadcast monitors, but I would prefer to send projects to an experienced colourist. It just seems crazy sitting in the post house watching the guy grading redspace without a LUT.

There is a company that will make LUTs for you, but they charge about 400 pounds and I don't see why we should be paying for that when it is really something the post houses should be looking into.

I don't understand what you're getting at here. Post houses that are set up around DaVincis in both film to tape and tape to tape environments are video based. That's what they use for source material. If you bring them log coded, file based data formats you're not giving them what they are set up to use. There are two solutions to this: either give them video (NOT Redlog coded files), or go to a DI type facility that is designed to finish from file based formats (NOT a video based DaVinci room). Many post houses have digital intermediate capabilities, and most of them have video monitors and scopes in those rooms, as well as a very experienced colorist. Perhaps you should talk to them about going that route rather than using something that isn't as appropriate for your purposes.

 

[Irri]

Well, what would send a DaVinci based post house?

 

[M Most]

Well, what would send a DaVinci based post house?

Video. Either on videotape, or in the form of files. Those files could be Quicktime files (I'd recommend some kind of uncompressed HD format, like a Kona or Blackmagic codec, although ProRes would probably be OK as well), DPX files (but not log coded), Tiff files - whatever you want. The point is that to color correct in a video environment, as you do with a DaVinci, your source should be in video color space, with video gamma - not logarithmic.

You know, for all of the insistence, here and elsewhere, that color correction for a video deliverable has to be done from pristine 4K files with everything that the sensor captured, the fact is that essentially all network television in the US is color corrected tape to tape from best light dailies on HD videotape. And an awful lot of it looks pretty darned good. I would venture to say that if a lot of the projects talked about here looked as good as most network television dramas, those who are making them would be pretty thrilled. It's not necessarily the specific methodology that accomplishes that, it's all about having well shot original material and talented people in post who can make it sing.

 

[Irri]

It's not necessarily the specific methodology that accomplishes that, it's all about having well shot original material and talented people in post who can make it sing.

I couldn't agree more. However, I am trying to give those people the best chance they can get. I've had a lot of complaints about skin tones when using 10 bit REC709 DPX sequences, and know of several DoPs who have re-rendered to redlog late in the day to get better results.

I completely see your point about sending footage in a video colourspace and would love to send them 16bit tiffs if the machines could handle it. Maybe, I'll render out redlog and REC709 DPXs as well as REC709 tiffs and let them decide. I just want to wash my hands of the decision.

 

[M Most]

I completely see your point about sending footage in a video colourspace and would love to send them 16bit tiffs if the machines could handle it. Maybe, I'll render out redlog and REC709 DPXs as well as REC709 tiffs and let them decide. I just want to wash my hands of the decision.

16 bit Tiff files have no purpose in HD video, because video is either 10 or 8 bits. When I said "video," that's what I meant - 10 bit HD video. That's what a DaVinci gets fed. That's what it wants to see. How it is fed is up to the post facility, but in most cases it's either from a videotape or a digital disk recorder that can be controlled as a VTR (RaveHD, Clipster, etc.). In either case, what the DaVinci will see is video, fed over single or dual link HD-SDI. Whatever you give them, that's what it's going to be turned into, however they choose to do that. You should ask them what they want before you take a lot of your own time creating things they won't use.

 

[Irri]

So a DaVinci works internally at 10 bit? You'll have to forgive me as I come from a shooting background so I am just working my way around the post side of things. When using Apple Color I have the option to use 16 bit float and I assumed a Davinci was more advanced and would thus be able to work in at least the same depth.

 

[M Most]

So a DaVinci works internally at 10 bit? You'll have to forgive me as I come from a shooting background so I am just working my way around the post side of things. When using Apple Color I have the option to use 16 bit float and I assumed a Davinci was more advanced and would thus be able to work in at least the same depth.

No, a DaVinci works internally at 32 bit float, 8:8:8 sampling. But you're not starting out inside the DaVinci, you're starting out as an HD-SDI input. As I tried to explain before, the DaVinci 2K is not a data driven device. It does not have data input and cannot read data files. It has no data storage as it's not designed that way, it's designed to pass through video in real time. Its inputs are video, and its outputs are video unless it is specifically set up as a data system - not the case in most video facilities. You seem to want to make it something it's not. I started out all of my comments here by pointing out that if you're not using a video work path, a DaVinci is not an appropriate device to deal with your material, no matter how much you may want it to be, and no matter how much you may like the colorist that's running it. That's still the case. Unless you're willing to transfer your Red material to a video format prior to color correction, you really should forget about using a video finishing device.