Is it possible to get wide gamut color out of Scanstation scans (color primaries wider than sRGB/REC709 locations)??

[Dan Baxter]

LG aren't clear about what's going on under the hood, but they may have a reason. There's no clipping in the colour scopes so it doesn't look like anything is clipped it may just be transformed from sRGB space using an LUT which is not necessarily a bad thing. The way that colour comes off most scanners involves a lot more work, one operator who runs an older model Scanity (he doesn't know exactly how old it is as he's just an employee) told me basically "The ScanStation is something else if that's really the way colour comes in the scan. We spend a lot of time on colour correction with the Scanity." In short, there's no evidence that anything the raw hardware is capable of is actually missing in the scan, and comparing against other scanners would be the wrong way to go about it even if you buy the same camera and lens and put it in a XENA as you would need to take out the LG light and program it to work exactly the same way otherwise it isn't like-for-like.

The Blackmagic Cintel doesn't go straight to Rec709, but they do still provide their own import LUTs and something about the import for prints has been proven to be problematic (whereas it isn't for negatives). To get to Rec709 involves a secondary colour LUT that the user has to create themselves, so more work. That's the same for most Bayer scanners, they capture raw or if they don't they may mess up the quality (for example the Moviestuff software crushes the capture and you lose detail). What LG is doing isn't necessarily a bad thing if nothing is lost or if there's minimal colour detail lost.

On 10/22/2022 at 1:19 PM, Larry Baum said:

It would seem a horrible shame to think of many films that got their one and only scan done without anyone realizing that the color gamut was clipped and that maybe for all time the original colors will be lost as the original film rots and fades and the digital archive failed to capture all the colors.

The scans are only as good as the person operating the scanner anyway. The ScanStation isn't exclusively for restoration work, it is a trusty reliable all-round workhorse. It can be used in different ways and it does what it's told. You can tell it to give the film its best effort, or you can tell it to make some quick proxies. If you're using it to inspect film it has a very nice built-in editing table and when a splice opens it reliably stops the scan and tells you to fix it. Some of the older scanners if you walked away from them to make a quick cup of coffee while they're doing their work at 7+ seconds per frame would un-spool the film onto the floor if you weren't there to babysit it when a splice opens. Many other scanners break down a lot, it doesn't. It'll scan on reels or cores it doesn't mind. It'll handle almost any film including film that's too badly warped for other scanners. Most of the time it goes straight to a deliverable format which is more than what most other scanners will do ("DPX-only").

There's a zillion different uses for them, you don't ever have to use it for restoration and you could still derive value out of it. As way of example, MemoryLab purchased their one pretty much just for home movie scanning. They had a choice to buy the Archivist, but when I asked last year why they chose the ScanStation they said it represented better value for them and they felt the increase in the cost was justified and they wanted maximum resolution for 8mm.

We'll get to the bottom of the colour gamut eventually. In professional settings, and this comes from multiple users not just one, most clients want Prores which is compressing beyond DNG or DPX anyway. For many the standard is to offer Prores XQ or HQ as the standard choices, it's made so that it can make the compression for you with minimal detail loss.

[Robino Jones]

On 10/21/2022 at 7:19 PM, Larry Baum said:

I dunno, I wish I was wrong, but it is starting to seem like I was likely correct.

Can you post examples? And if you don't have any examples on hand, shoot some film and have it scanned by Robert on his Xena and LG - a third scanner like the Scanity HDR would be helpful as well for comparing the results. Share your tests here so we can look into what you're talking about.

There might be a simpler reason why LG is not getting back to you. You might "feel" that you are correct but without anything to back it up it's not worth much.

Edit: Also get a DSLR scan of the same film, you said they had wider color gamut. 

Edited October 23, 2022 by Robino Jones

[Robert Houllahan]

Again.

CFA based scanners like the Scan Station Xena-Color Kinetta HDS+ VarioScan which can all use the same make-model of sensor will have the sensor CFA Dyes (lots of cross-talk there) a combination of LED RGB lamp diodes, those diode color center temps and set RGB lamp balance at the front end then the Demosaic math and color transform matrix and or LUT at the back end to make a finished scan. All of these machines will have different specific engineering choices along each part of the imaging path.

I did a test and advice on setup of a Xena in the U.K. a while ago where I scanned a LAD and TAF on the Scan Station the Spirit and the Xena and we set the initial Xena color transform matrix (something you can get to on the Xena and which is "underhood" on other scanners) so the color accuracy was right on his Xena. Eventually the three scans matched pretty closely with some minor differences.

In the "True RGB" Spirit PhantomII control software there are color balance lamp output and other color correction tools to get the scan in range on the scopes. So every scanner is not just pushing an automatic button to get the best scan from any specific stock. So for that test I had to setup the color on the Spirit too and make specific choices in the scanner setup which seemed most accurate.

This test was done before I acquired the Arriscan and I would have used it in 2-flash 16bit mode for that as I think it is a "gold Standard" for scanning and accuracy.

If I scan a TAF and a LAD on my Arriscan, Xena and Scan Station I think there will be some differences and that once a colorist gets their hands on the scans that they can make the colors match pretty well.

I think a "True RGB" scanner like the Arriscan or Xena RGB or LaserGraphics Director will still be the goto for high end work and will make a more color accurate scan.

That said I have not had many people who had issues with Scan Station scans for lack of color accuracy. I setup the Scan Station scans with the color grading on and usually for negative a gamma of 1.0 and then trim the hilite and shadow controls so there is no clipping in the scopes and they look good. The scans are not clipped in the scanner scopes nor are they in Resolve or Nucoda and they seem to be able to be graded easily.

YMMV

[Dan Baxter]

15 hours ago, Robino Jones said:

There might be a simpler reason why LG is not getting back to you. You might "feel" that you are correct but without anything to back it up it's not worth much.

Just to clarify for you, his scanner is one of my friends. We haven't reached the same conclusion he has. But yes LG can be a pain with communication.

15 hours ago, Robino Jones said:

And if you don't have any examples on hand, shoot some film and have it scanned by Robert on his Xena and LG - a third scanner like the Scanity HDR would be helpful as well for comparing the results.

We can test ScanStation vs ScanStation (same model run the same way) at some point, no need to test against completely different scanners. If Robino sends over a colour chart we could re-scan it on another ScanStation quite quickly and then it'd be obvious if one wasn't getting perfect colour. We can already test the same gen Sony Pregius in other scanners as it is, there's really no need to bother Robert unless it would be useful for him to do a comparison perhaps against his SS Personal - but as he already has a Xena I think the value would be low. There's no clipping in the colour scopes.

3 hours ago, Robert Houllahan said:

That said I have not had many people who had issues with Scan Station scans for lack of color accuracy. I setup the Scan Station scans with the color grading on and usually for negative a gamma of 1.0 and then trim the hilite and shadow controls so there is no clipping in the scopes and they look good. The scans are not clipped in the scanner scopes nor are they in Resolve or Nucoda and they seem to be able to be graded easily.

Yep, my mate's not having an "issue", he just wants to make sure it's working as best as it can.

[Carl Looper]

I would conclude from the discussion that the scanstation software doesnt provide for  selecting an encoding colour space larger than the Rec.709 triangle. I imagine the sensor would be capable of doing so were it programmed to do so, but given the apparent absence of such an option in scanstation software (based on commentary by those who run scanstations) its a reasonable assumption to make that it only encodes in terms of the Rec.709 colour space. 

[Robert Houllahan]

19 hours ago, Carl Looper said:

I would conclude from the discussion that the scanstation software doesnt provide for  selecting an encoding colour space larger than the Rec.709 triangle. I imagine the sensor would be capable of doing so were it programmed to do so, but given the apparent absence of such an option in scanstation software (based on commentary by those who run scanstations) its a reasonable assumption to make that it only encodes in terms of the Rec.709 colour space. 

I do not see any examples or technical data offered or linked to within this thread to make any conclusions from. 
 

Is there any technical examples which form the basis of this assumption? I am not saying it is wrong but some data to draw from would be better than speculation.

 

 

 

[Dan Baxter]

19 hours ago, Carl Looper said:

I would conclude from the discussion that the scanstation software doesnt provide for  selecting an encoding colour space larger than the Rec.709 triangle. I imagine the sensor would be capable of doing so were it programmed to do so, but given the apparent absence of such an option in scanstation software (based on commentary by those who run scanstations) its a reasonable assumption to make that it only encodes in terms of the Rec.709 colour space. 

Don't make conclusions from this discussion. You can make it go a little bit beyond the Rec.709 colour space and get wide gamut using very specific scan settings, but we're still not sure if it really matters or not. It isn't clipping anything, it seems to be that for most formats what it does is use a LUT to convert the full gamut into Rec.709. That isn't necessarily a bad thing because if it didn't do that you'd get clipping if you did no post colour correction. Please have a look sometime at how the Blackmagic Cintel works - Blackmagic supplies the user with LUTs they have to use to convert the scan into a usable colour space in Resolve, so that the LG does this under-the-hood for you isn't necessarily a bad thing, it doesn't mean you're losing anything, it doesn't stop you doing HDR grades, it doesn't appear to be irreversible, and it cuts down the post-scan work required to make a deliverable file. That is to say if the scan has 10-12 true stops of dynamic range in it, it doesn't appear to be losing any of the dynamic range in the Rec.709 conversion.

Also trust me on this: lots of Lasergraphics users think they know more about them than they actually do, we've discovered stuff that nobody else has known. I'm not talking about the obvious stuff that any professional company knows about. Yes there's an absence of under-the-hood settings, but again that's not really a negative. Even with a scanner as seemingly basic as a ScanStation in terms of software settings, the average user still has enough trouble as it is making them do consistent quality work. If you could change every under-the-hood setting you would quickly break it. As an example - let's say you need to scan without the diffusion concealing the base scratches because you have a job that requires you see all the film damage: a ScanStation can't do that. If you put something in front of the light to to make the effect go away then it gets confused and it can no longer find the perfs to register the frame. So that's an under-the-hood setting and changing it would require rewriting the capture software and providing an entirely new light-box with a software setting allowing you use the diffusion to hide damage or to make it visible. If enough users wanted that feature I'm sure they could add it, but most users would just use another scanner for jobs like that. So the point is that just because there's an under-the-hood setting that you can't change, it doesn't necessarily mean that it's a bad thing - if you want complete control over everything you can always commission a DCS Xena!

[Carl Looper]

In terms of capturing (to file) the full chromacity range of the film, an encoding in terms of Rec.2020 would be better than Rec.709. This requires at least 12 bits per colour component. The opto-electric transfer function (or "gamma") of Rec.2020, is exactly the same as Rec.709. If Rec.2020 otherwise achieves a wider gamut encoding, it's only because it uses more bits. To put it another way, (ignoring the change of hue for the primaries) a 10 bit version of Rec.709 encoding will have a larger triangle in chromacity space than an 8 bit encoding. The difference in primaries between Rec.709 and Rec.2020 just means the shape of the gamut triangle remains within the visible chromacity range, i.e that the bits required to encode the full chromacity range of the film don't have bits wasted on invisible chromacities. In principle, (apart from said waste), a high bit encoding, using Rec.709 primaries, can be transcoded to Rec.2020 ( in downstream processes), without any chromacity loss. In practice, the waste factor is important as it affects file sizes. It is more optimal to alter the primaries (in particular green) to keep file sizes in check. Which is what Rec.2020 does.

[Carl Looper]

The lack of technical documents regarding how ScanStation scans a film when particular setting are applied, and that operators of ScanStations appear to have no idea what you are talking about when talking about colour spaces, means that one is left to hypothesise what the result of a scan might be. In practice, of course, scans can be eyeball adjusted in software such as Resolve, and most colours will be reconstructable through that process. It's when otherwise using a scan of a film print to assess that film print (e.g. ahead of making a better print) that the specifics of the encoding become important. One might very well take a scan through Resolve and make a beautiful digital result from it, but how to otherwise use that grading information to make a new projection print, is entirely lost if a scan house (or Lasergraphics) can't or won't describe the scan in terms of the transforms it uses to encode the scan. That all said, a combination of speculation (hypothesising) and tests of such would eventually solve for such lack of information.

 

[Dan Baxter]

2 hours ago, Carl Looper said:

In terms of capturing (to file) the full chromacity range of the film, an encoding in terms of Rec.2020 would be better than Rec.709.

Film doesn't have a gamut as wide as Rec.2020 and Rec.2020 isn't full gamut either. Anyway we know how to force it to do full gamut... but what we don't know yet is whether it matters at all to the final quality. That will require further testing with the right type of film.

1 hour ago, Carl Looper said:

The lack of technical documents regarding how ScanStation scans a film when particular setting are applied, and that operators of ScanStations appear to have no idea what you are talking about when talking about colour spaces, means that one is left to hypothesise what the result of a scan might be.

There's a WIP manual for it now that's available to users... previously you're correct there was very little in the way of documentation.

1 hour ago, Carl Looper said:

One might very well take a scan through Resolve and make a beautiful digital result from it, but how to otherwise use that grading information to make a new projection print, is entirely lost if a scan house (or Lasergraphics) can't or won't describe the scan in terms of the transforms it uses to encode the scan.

I'm really not following you here Carl. You can't just scan a film and expect the scan to look exactly like a brand new projection print without any colour work. For many scanners grading is difficult, try grading a faded film off a GodenEye sometime - you won't be impressed.

[Robert Houllahan]

3 hours ago, Carl Looper said:

The lack of technical documents regarding how ScanStation scans a film when particular setting are applied, and that operators of ScanStations appear to have no idea what you are talking about when talking about colour spaces, means that one is left to hypothesise what the result of a scan might be.

How is this different than any other film scanner? I have Scanners from Arri DFT DCS and LG and none of them have any color gamut space settings, in the case of DPX they scan to 10bit log (12bit) or 16bit linear.

The Arriscan for example is setup to the film base (RGB+IR LED lamp intensity) and then Linear to Log conversion with the ability to set Cineon values.

Other scanners have color correction tools in the scan setup to do matching and balance etc. but nothing specific to Rec709 or 2020 etc. I think for negative they are all based on the Kodak Cineon code values from the 1980's on.

[Carl Looper]

4 hours ago, Dan Baxter said:

Film doesn't have a gamut as wide as Rec.2020 and Rec.2020 isn't full gamut either. Anyway we know how to force it to do full gamut... but what we don't know yet is whether it matters at all to the final quality. That will require further testing with the right type of film.

There's a WIP manual for it now that's available to users... previously you're correct there was very little in the way of documentation.

I'm really not following you here Carl. You can't just scan a film and expect the scan to look exactly like a brand new projection print without any colour work. For many scanners grading is difficult, try grading a faded film off a GodenEye sometime - you won't be impressed.

So a projection print is improved by adjusting printer points on the printer. The traditional devices used for assessing an answer print are colour analyser cameras and densitometers. One could also use a scan of the print for this. But not if the transforms used to encode the scan are opaque.

This is not about how a scan "looks" but what the resulting numbers on file mean, i.e in terms of the physical light transmitted by the film. If the files are encoded in terms of known standards, such as Rec.709, or Rec.2020, or any other known standard, it is then simple enough to grade the print, and compute the required compensation for the printer lights.

I only mention Rec.2020 as it's gamut triangle is a reasonable match to print stock gamut, without bit wastage. One could, of course, use an even larger colour space, if at the expense of larger file sizes.

[Carl Looper]

3 hours ago, Robert Houllahan said:

How is this different than any other film scanner? I have Scanners from Arri DFT DCS and LG and none of them have any color gamut space settings, in the case of DPX they scan to 10bit log (12bit) or 16bit linear.

The Arriscan for example is setup to the film base (RGB+IR LED lamp intensity) and then Linear to Log conversion with the ability to set Cineon values.

Other scanners have color correction tools in the scan setup to do matching and balance etc. but nothing specific to Rec709 or 2020 etc. I think for negative they are all based on the Kodak Cineon code values from the 1980's on.

I have no idea how other scanners compare. My interest in Scanstation is only because a local scan house has one, and I want to use it for grading a print.

[Carl Looper]

5 hours ago, Dan Baxter said:

Film doesn't have a gamut as wide as Rec.2020 and Rec.2020 isn't full gamut either. Anyway we know how to force it to do full gamut... but what we don't know yet is whether it matters at all to the final quality. That will require further testing with the right type of film.

There's a WIP manual for it now that's available to users... previously you're correct there was very little in the way of documentation.

I'm really not following you here Carl. You can't just scan a film and expect the scan to look exactly like a brand new projection print without any colour work. For many scanners grading is difficult, try grading a faded film off a GodenEye sometime - you won't be impressed.

So just to clarify, in case my previous response remains confusing. So in my case, the question of how a scan describes the light transmitted by the film is with respect to the question of how a new print, with new printer light settings, can be made from the original neg, i.e. for projection in an analog film projector. Nothing to do with how a scan might be graded, or otherwise escape such grading. 

 

[Robert Houllahan]

The simplest way to describe how the scanner translates the print to digital is that the scanner sensor is a monochrome sensor and each color is then illuminated with Red , Green or Blue light and each time that light is fired then the sensor takes a picture representing the color which is then mapped into the DPX frame file as linear data.

The Red Green and Blue light intensity are set by measuring the sensor output and setting the intensity of the light through the base at it's clearest so the sensor is close to but not clipping, then the rest of the sensor DR is just down to the shadows...

For the Scan Station using a Sony Pregius 6.5K camera it is 12bits for single flash and 14bits for HDR double flash so that is then mapped as linear data into 10bits or 16bits for DPX without a Lin to Log conversion table.

You could shoot out a Kodak Digital LAD and measure the AIM Density on a Xrirte Desnitometer, print that and measure it again then scan it and match the AIM charts to the code values in the scanned DPX frame.

For prints it is all linear data.

For making a film to film print there is also always the printer lights base setup and the color timer adjustments. There is no fully automated human decision free way to do film printing but there are the Kodak LAD control tools which allow a high degree of consistency to be made.

[Carl Looper]

Linear encoding is probably the safest option for a scan (involving the least number of assumptions in downstream processing) but it is also the most inefficient in terms of file sizes. Any "corner cutting" on such, (e.g. dropping bits) is going to compromise the data faster than if the scan was encoded in any of the non-linear ways it might be encoded. The most conservative non-linear encoding will be linear to Log encoding. Dropping bits in a log stream will have less affect on integrity than if dropping bits on linear data. Log encoding is also the first (and simplest) attempt to transform linear data according to a human perceptual understanding of light. Following on from log encoding (in terms of efficiency) is gamma encoding. A standard that has remained strong over the years is the one standardised in Rec.709. Indeed newer standards, such as Rec.2020, maintain the same gamma encoding as Rec.709. The main change between 709 and 2020 is the green primary - a change required to keep the resulting expanded colour space within the bounds of visible light (which avoids bit waste). 

Kodak LADs are good for calibrating printer lights, but as far as I know, they are not available for 16mm. I wish they were ! Nevertheless the basic idea behind a LAD is a good one. A LAD can be spliced to the head of a print, providing the means by which to characterise whatever transfer function is being used by a scan. 

Once a scanners transfer function has been characterised, software can be written to emulate, on a computer screen, what the film would look like when projected on an analog projector. Any deviation from an ideal result can then be translated into printer point corrections to be made on the printer.

This workflow does not imply some sort of machine is making colour decisions. It just provides the means by which a colourist, using their eyeballs and experience, can make decisions translatable back into printer configurations (such as printer point adjustments).

 

[Robert Houllahan]

On 11/23/2022 at 4:23 PM, Carl Looper said:

Linear encoding is probably the safest option for a scan (involving the least number of assumptions in downstream processing) but it is also the most inefficient in terms of file sizes. Any "corner cutting" on such, (e.g. dropping bits) is going to compromise the data faster than if the scan was encoded in any of the non-linear ways it might be encoded. The most conservative non-linear encoding will be linear to Log encoding.

For film data scanning there is linear and Cineon-Log encoding, No other type of log encoding is used nor wanted.

Cineon Log was invented by Kodak in the 1980s to scan negative films and it's Log curve matches the sensiometric density characteristic of film negative as a way to compress the linear sensor response and make the bits more useful in post.

All CCD and CMOS sensors are linear devices i.e. more photons increase voltage output in a linear manor. The point of using Cinelon-Log was to take 12-14-16bits of data per pixel and scale them into 10bits.

Film positives are not scanned with a Cineon Log curve they are scanned as linear data because the print is "wysiwug" and linear encoding works for that.

ideally you would scan at 12bit 14bit or 16bit and just put those bits into a 16bit DPX file as linear data and go about processing from there, this amount of data becomes unmanageable for most computers and disk systems, so we have 10bit DPX and ProRes which most people use.

Film scanning has never primarily been about efficient files sizes it has been about a accurate and full representation of the density scale color and resolution on the film.

[Robert Houllahan]

On 11/23/2022 at 4:23 PM, Carl Looper said:

Kodak LADs are good for calibrating printer lights, but as far as I know, they are not available for 16mm. I wish they were ! Nevertheless the basic idea behind a LAD is a good one. A LAD can be spliced to the head of a print, providing the means by which to characterise whatever transfer function is being used by a scan. 

Once a scanners transfer function has been characterised, software can be written to emulate, on a computer screen, what the film would look like when projected on an analog projector.

LADs are available for 16mm we use them all the time.

The Kodak LAD system is not just a good system it is the system by which analog and digital elements are managed. There is no need to "characterize" the scanner. There are several systems which are used to profile digital displays and full end to end lab scanning film recording and printing to allow a colorist to grade using a digital projector which looks like the film print the lab will make.

 

[Carl Looper]

I would have assumed the Prores encoder would use gamma encoding, rather than storing linear or log data. Or is that not correct? 

Othewise dropping linear data down from 12/14/16 to 10 bits (dropping the least significant bits) is the worst thing one could do. Poor mans compression. Better is to firstly transform the linear sensor data to log, before digitising the result as 10 bit data. Even better is to perform gamma encoding prior to 10 bit digitisation. But only if the gamma function is known, otherwise the relationship between the original linear data and the gamma encoded values is severed. In other words, if the Prores encoder is performing gamma encoding (as would be sensible) it would be good to know which gamma transform it was using. Given the gamma transform, the original linear signal can be reconstructed (to a good approximation) using the inverse transform. And given a reconstruction of the linear data, the original light can be reconstructed from a plot of the sensors spectral curves. If the prores encoder otherwise remains opaque, a log file would be the next best thing. 

Does the scan station DPX encoder support log encoding? Or just linear?

 

 

 

 

[Robert Houllahan]

3 minutes ago, Carl Looper said:

I would have assumed the Prores encoder would use gamma encoding, rather than storing linear or log data. Or is that not correct?

I don't know how to say this more clearly.

Negative scans are encoded as Cineon-Log.

Positive scans are linear data.

This has been the case since the early 1990's

https://en.wikipedia.org/wiki/Cineon

 

[Carl Looper]

36 minutes ago, Robert Houllahan said:

LADs are available for 16mm we use them all the time.

The Kodak LAD system is not just a good system it is the system by which analog and digital elements are managed. There is no need to "characterize" the scanner. There are several systems which are used to profile digital displays and full end to end lab scanning film recording and printing to allow a colorist to grade using a digital projector which looks like the film print the lab will make.

 

Unless the transforms used by a scanner (along with a spectral plot of the sensor sensitivity) are made available, a developer writing software to process the scans has no choice but to characterise the scanners encoder, eg. with a LAD test or some other understood test strip.

How else would they otherwise know how to read the data and render it in the context of a given display? 

Certainly there will be existing solutions that do this, but if they are any good they will have done a characterisation of the scanner's particular encoder. 

 

 

[Carl Looper]

31 minutes ago, Robert Houllahan said:

I don't know how to say this more clearly.

Negative scans are encoded as Cineon-Log.

Positive scans are linear data.

This has been the case since the early 1990's

https://en.wikipedia.org/wiki/Cineon

 

Just because there is a claim that cineon encoders stored linear data for positives doesn't mean a Prores encoder does. Or am I missing something?

 

Edited November 26, 2022 by Carl Looper
clarification

[Carl Looper]

30 minutes ago, Robert Houllahan said:

I don't know how to say this more clearly.

Negative scans are encoded as Cineon-Log.

Positive scans are linear data.

This has been the case since the early 1990's

https://en.wikipedia.org/wiki/Cineon

 

My understanding of cineon was that it stored densities, which is log data (the log of inverse transmittance). Not linear data. And that this was how prints were encoded as much as negatives (but not requiring as many bits). However it's a moot point. What were interested in is how the scanstation Prores encoder stores data as this will be (I assume) more efficient than DPX (especially if the DPX is truncated DPX).

Edited November 26, 2022 by Carl Looper

[Carl Looper]

2 hours ago, Robert Houllahan said:

Film scanning has never primarily been about efficient files sizes it has been about a accurate and full representation of the density scale color and resolution on the film.

The various non-linear ways in which film might be encoded is about how to maintain accuracy when otherwise required to reduce the file size. For example, if the target file size is to be 10 bits (for whatever reason such as cost), the worst approach would be to truncate the linear sensor bits. As prevoiusly mentioned, more efficient (in terms of accuracy) is to compute the log of the linear sensor data, and truncate that. 

Of course, if cost is not a concern then saving the linear sensor data will be the most accurate.

But if cost is a concern (which, for most mere mortals, it will be) then 10 bit gamma encoding will be more accurate than 10 bit log encoding, and 10 bit log encoding will be more accurate than 10 bit linear data.

C

 

 

 

 

[Robert Houllahan]

The Cineon file format was designed specifically to represent scanned film images, and thus has some differences from other formats such as TIFF and JPEG:

• The pixel data represents "printing density", the density that is seen by the print film. Thus, Cineon files are assumed to operate as part of a reproduction chain keeping whatever values are originally scanned from a negative or positive film. Any negative can be reproduced on the recorder retaining the original neg's characteristics (such as color component crosstalk and gamma correction) — and thereby retaining the negative's "look" if it were directly printed. The original Cineon color data metric printing densities were based upon 5244 intermediate film. Conversion of Cineon Printing Density (CPD) to Status-M can be estimated with a 3x3 matrix or by using tables contained in the Kodak "Digital LAD" document. This document shows a specific relation between Cineon Code values and Status-M densities.
• The data is stored in log format, directly corresponding to density of the original negative. Since the scanned material is likely a negative, the data can be said to be "gamma with log encoding".
• To evaluate original scene luminances from Cineon data, the camera negative characteristics must be known. (Such characterization is known as "unbuilding.") Such characterization is aided by exposing a sensitometric strip so that the actual developing gamma can be determined. The film can be unbuilt by using the unique per-layer contrasts of the color negative.