Color Management/custom profiles at capture - slides

The answer depends on your images and your gear. I’d give both lenses a try and would expect the Sigma to render more evenly. As for exposure/bracketing etc., your source material will teach you.

Take a few shots of different slides that exhibit extremes as well as not and post them here…if you want hints that relate to something other than to thin air.

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Well, you have thousands of slides and they are old slides, presumably from a variety of different films, the colours may have faded and there probably won’t be an IT8 target for some/many of the films you are trying to copy, you may not even know what films they were shot on. Although there are several easily accessible ways to make a camera profile for a given lighting setup using standard software (Lightroom, Capture One etc.) the only ones I know use reflected targets such as the Macbeth Color Checker or X-Rite Passport, or even Passport SG.

It is generally only dedicated scanner software such as Silverfast or Vuescan that can make use of the IT8, so-called “IT 8.7 or ISO 12641 compatible software”. I do have a friend who has succeeded in making his own profiles using bespoke colour profiling software but it certainly wasn’t straightforward though it was effective, and you’ll also find that the software required can be pretty expensive. In fact the only mention of such a profile used for camera scanning that I’ve seen is from the high end DT Heritage where they include a profile for their light sources in their dedicated software, but that’s a very expensive system of course. As you’ve found out it doesn’t seem to get discussed in digital camera scanning forums. Now that might be because we just want to get the best from our slides and not be tied down to the colour produced on film, and that’s an equally legitimate perspective, we’re not trying to reproduce the Mona Lisa.

I’d definitely take Digitizer’s advice and seek out a selection of potentially ‘difficult’ slides, dense, thin, faded etc. and then see how, if at all, they fall short of your expectations. I’d also settle on one lens and maybe use Vlads Test Target to choose between them, it will be fine for this, and may also show up any potential problems with flare etc. Of course you’ll be shooting on RAW so provided the technical aspects are correct the colour can be sorted at any time.

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I’ll just add one more point whilst I think of it. For absolute perfection you would need to remove the slides from their mounts and photograph them held completely flat, under Museum glass perhaps. Do you really want to be doing this? Personally I think it’s kind of a shame to do this with a family archive, particularly with those lovely Kodachrome card mounts. That’s where stacking comes in as an alternative I suppose but you don’t want to make the whole process so onerous that you never complete the project.

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Just a point re the dense areas of transparencies or negs - these are far better reproduced with a camera based digitising setup than with a scanner. With a scanner the amount of light that can be squeezed through the dense area is fixed by the scanner beam speed and brightness and this leads to noisy results or lost data. With a camera based system this can be increased without practical limit. If necessary a separate exposure for these areas can easily be HDR combined with exposures for the other areas.

I have recently digitised thousands of slides with my camera set-up and am constantly amazed at the amount of information that can be extracted from the dense areas, particularly Kodachrome. I used to produce slide presentations and project them with four Carousel SAV2000s combined with two Electrosonic dissolve units on twin screens. I was pretty impressed with the results.

Now with a digital projector and the visual options available for presentation with an application such as “Keynote” I am “blown-away” with the image quality and sharpness that has been previously unseen in those transparencies. They compete incredibly well with current photos shot on a digital camera!

As you seem not to be an easily fend off type, and also because of your funny grandpa, let’s elaborate some bits.

Bracketing could be useful and yes, the exposure should be for highlights. Depending on your camera’s ISO performance it may not be necessary to actually shoot several exposures. Would be sufficient to just convert the raw file with different exposure compensations and merge those. I’m not familiar with R5 but as a recent camera it should easily handle +2 stops compensation without making the noise any more apparent. Naturally, use the minimal native ISO when shooting.

Unfortunately, the issues of a high contrast input do not disappear with this approach. Diffraction doesn’t go anywhere with any kind of area sensor. Relatively even areas where the density differences are small should come out fine, but areas of high local contrast should be watched for flare spillover. The only truly efficient alternative is dot scanning, which drum scanners use. One thing to try would be to use a higher-than-target scanning resolution with a lens having higher than 1:1 ratio and then resize the image down.

This is where the rigs based on scanner lenses come into play. These have way better performance than consumer macro lenses, but often can’t capture the whole film frame at once, meaning stitching - another dimension of complexity.

Evenness does not need to be a factor. Use flat field correction both when preparing the profile and when shooting the slides. In addition to the lens vignetting this will also take care of any unevenness of the light source.

The Canon lens is fine, it should give around 4200-4600 ppi on the R5 sensor, which is likely sufficient. The Sigma one is likely sharper, but I wasn’t able to find any measurements.

While it is true that IT8 transparency targets are typically used in traditional scanning, there is nothing that prevents one from using them with DSLR as we will shortly demonstrate. For making an ICC profile the target doesn’t need to be a particular one. ColorChecker, IT8, reflection, transparency, anything. One can take a sheet of paper, put some oil and acrylic paints on it in squares, and call it a target. As long as the patches were measured with a spectro, and the target layout description file exists, it will work fine. A profile can be created and will be very much more useful for images of the same kind than no profile at all.

The procedure itself is not difficult, but one does need to do the homework. The software is open source, free, modern, high quality, and comes with a decent amount of community support. One can get it here, although this is not the only choice available.

Just to avoid further confusion, reproduction is a completely different problem domain with dissimilar constraints. What we all are mostly going for is a faithful interpretation of the look, which is already a very tall order if we consider the technicalities.

Without calibration it really can’t.

Flatness is a valid concern and it does need to be addressed. There are various approaches, e.g. ANR glass backing, all kinds of scanning frames, and the suggested focus stacking. Given that you (OP) already got a scanning rig, this issue should be familiar. Museum glass, as well as e.g. polarizing filters, are not advisable as these modify the spectral composition of light and, additionally, may interfere with the spectrum of the lightsource.

Besides, while 96-98 CRI lighting sounds reassuring, its worth it to measure the light composition with a spectro to be aware of the peaks/dips, and, more importantly, know which colors are the outliers. CRI rating calculation has important deficiencies which are rather relevant for scanning.

That mostly depends on the scanner and the software. The usual film scanner choice, the Epson family of scanners culminating with V850 and all the way back to 4990 in combination with VueScan allows modifying the (real, analogue) scanning exposure and offers multiscan (i.e. HDR). The deficiency of flatbed scanning is really not the exposure control, and not even the single-pass dynamic range. It is the low resolution (~2200 ppi) and the wait. That’s the primary reason DSLR scanning beats flatbeds. A ~45Mpx camera with a decent 1:1 macro lens achieves around 4600 ppi and is much faster, that’s all.

Before we look at an example of DSLR calibration using a transparency target, let’s stop for a moment and consider all the steps one needs to perform in this seemingly fast way of scanning.

Preparatory steps

  • Take a flat field capture (at the beginning of each scanning session)
  • Prepare the ICC profile (once for a DSLR / lens / target / lightsource combination)

Scanning steps, for each frame

  • Capture a normal single exposure
  • Do focus bracketing (unless the alignment is good)
  • Do exposure bracketing (unless after-the-capture compensation gives good results)

Processing steps, for each capture

  • Interpret the RAW
  • Apply the flat field correction
  • Apply the calibration profile
  • Convert to a working space

Processing steps, for each frame

  • Merge the exposures
  • Merge the focus brackets
  • Save the master scan

Clearly, this all doesn’t look like something that should be done manually, especially when we are talking about “many thousands” of images. A meaningful automation seems to be a must, and that means scripting. That, in turn, means command line tools. This is another area where open source tooling beats commercial software pretty much every time. However, it also means more homework. This brings us back to the question of personal choice. Oh, well.

Now for the promised example. Here is a capture of a transparency IT8 target on a 35mm slide, this is how ACR sees it. Note the black background and some details at the sides. The background is a piece of black cardboard with a 35mm hole in it, where the target is inserted. The details at the sides are where the frame area turned out to be bigger than the piece of cardboard, should have been avoided, but not critical. By the way, this was shot through a regular zoom non-macro lens, just for fun. That’s why the target area only takes a fraction of the frame. The backlight is ~D50 sunlight.


Using dcraw, convert the image to a tiff:

dcraw -v -T -o 5 -j -M -6 -W -g 1 1 -w -c chart-capture.nef > chart-xyz.tiff

Explanation of the options can be easily found online. The important bit is the raw gets converted with the linear gamma. Note how because of that the result looks much darker:


Then, for an easier target detection, I cropped the image. This is not strictly necessary, but makes things simpler:


Now take the measurements from the scanned capture. scanin is a tool coming with ArgyllCMS. Again, the explanation for all the switches can be found online.

scanin -v -dipoan -G 1.0 -p chart-crop.tif it8Wolf.cht F210418.cie

The it8Wolf.cht is the target layout desctiption file, comes with ArgyllCMS. The F210418.cie is the target batch measurements data file, available from the vendor of the target. The result is an .ti3 file, not yet directly usable. In the meantime let’s check the diagnostic output of the target detection:


Everything seems to be located nicely.

Finally, creating the ICC profile. This is a matrix profile, which is preferred over LUT profiles on small numbers of patches:

colprof -v -D"My Profile" -qm -am -u chart-crop

The profile gets placed to the appropriate system folder, Photoshop gets started up, and here is the image with the profile applied:


Similarly the profile can be applied to any other frame, scanned in the same conditions. Is this profile any good? Let’s check:

profcheck -v2 -k chart-crop.ti3 chart-crop.icc
> Profile check complete, errors(CIEDE2000): max. = 5.832972, avg. = 1.372846, RMS = 1.638548

For a matrix profile of medium quality on a limited number of patches (IT8 is not a big target) the results are quite fine. Subjectively speaking, the image could be brighter, but that’s down to the original target exposure, and also to the -u setting of colprof. This disables the automatic exposure correction by the profile, personal preference.

As you can see, the procedure is not excessively difficult, and in fact, is easily automatable.

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slow clap Wow, once again thank you for the thorough response. I am blown away and will have to think on this and analyze it a few times to fully absorb all of it!

Thank you!

Also, I will post some examples soon. I finally got my settings recipe dialed in for aperture priority on the R5 + lens + light source for bulk slides. This has had a very, very helpful effect on limited post time for more accurate color.

  • center-weighted avg. metering,
  • f.5.6 ish (up to +/- 2/3 if it is flat or needs DoF)
  • min shutter 1/125, max any
  • +2/3 EV,
  • D+ (highlight protection, forces ISO 200 which is a sacrifice I make for volume/sped, could be talked out of this).
  • not framed at 1:1, more like 1:1.7 or so? Limited by projector + lens combo. Yields a 24MP crop but can get to 30MP if I push closer.
  • and using Adobe Neutral profile and controlling contrast and vib/sat sliders later
  • they all get -1/3 to -1 exposure and 0-30% highlights and they are rock solid looking.
  • minor tweaks to shadows to taste

Still want to make color profiles though to be discerning.

This gives a strong, fast automatic exposure using ETTR, great shadow detail/noise, a good baseline on color, and never blowing highlights. Also works great for the occasional -1.3/0/+1.3 bracket on problem slides. Should probably go even more ETTR after deeper analysis digging into the RAW files, too. Camera histogram is a liar as we know. I get around 700-1500 prepped slides scanned per hour this way depending on my personal focus. Selects get made and those are scanned vertically at 1:1 45MP.

@nicnilov I am pretty happy, generally with my light source for my bulk scans on my Dr. FranKodakenstein Projectoscanner™ (still workshopping this one :crazy_face: ) but I have bought some 35W/20W Solux halogen bulbs to test for closer to 100CRI spectrum in the future after I am done cam scanning the first wave here.

Generally will be trying to increase my my light, alignment and lens quality as time goes on, and especially interested in jumping from 14bit to 16bit at some point with a higher MP count for medium format stuff I have to do.

Though, generally lab and at-home testing results vs the real world execution of such things are often just differences of degree rather than magnitude. So perhaps I should be happy for awhile and not let perfection be the enemy of the good (or even great). Time will tell.

For more on some lenses I’ve recently come across a few solid links, 1 of which I’ve posted on NLP forum elsewhere. The other two, @Harry posted in another thread and were quite surprising to me. These focus on 35mm 1:1 reproductions for camera scanning.

1- 1X LENS TEST 2020 — Close-up Photography
2- 1x Macro Lens Test 2022 — Close-up Photography
3- How Good a Macro Lens do you Really Need for DSLR/Mirrorless Camera Scanning? - pixl-latr

Very interesting to read your method, as you would expect it’s similar to the one my friend uses except that he uses different software. I wonder if you could please explain what bearing the choice of IT8 target has on this - so Ektachrome, Fuji etc., even Kodachrome when such targets were available?

Would you see a difference in results given that the target might not match the film type of the originals?

Alternatively if you bought each of the currently available 35mm IT8 targets (5 from would the resulting profiles produce markedly different results?


Thanks nicnilov - I’ve been scanning for decades and still found lots of useful info in your post.

But re scanning dense areas I think your points above are more theoretical than practical. I’ve found multipass and analogue gain to give very little improvement in dense area repro. The speed of the scan beam and the max brightness are fixed and that puts a limit on what can be achieved this way whereas a DSLR exposure has no limit.

The difference I see with a DSLR is orders of magnitude better - and, of course, far quicker. Modern DSLR sensors also have a far greater dynamic range and, while that can to an extent be improved with the above techniques it still doesn’t hold a candle - or a candela :slight_smile: - to the DSLR output.

Generally this all looks valid, especially for preview bulk scanning. One point to consider is the automatic exposure. Is there really a reason for it? The maximum needed exposure is defined by the deepest shadows, which on slide film are within density 4.0. The minimum exposure is defined by the density of a clear film base, 0.05D. Density range of 4.0 in linear contrast terms is 10000, which in dynamic range terms is about 13.2 stops.

Your camera’s dynamic range at ISO 50 is 13.33Ev, which is a tight match. It means for the slides having the extreme dynamic range it would be rather difficult (and not desirable anyway) to take a single exposure accurately matching the image, calling for bracketing. For the slides not having such dynamic range any reasonable exposure will do, and it does make some sense to go ETTR.

However, when making a profile it is important for the target exposure to be correct, that is, the histogram reasonably spread and the middle gray being at 18% or 50 L* in L*a*b*. In order for the profile to be applied with precision, the image’s exposure should also be in normal range. Meaning if we take an overexposed image and apply a color correction via the profile, the particular densities of the image will be affected by parts of the profile curves destined for densities that are lower. If there is a significant non-linearity at different parts of the profile curve (which is not unusual), the result can be a misplaced correction.

Because of that it is advisable to scan most frames at a fixed exposure. This gives a more stable baseline, more suitable for profile-based correction.

Can’t comment on D+ without experience, but from the descriptions all it does is selectively boosts gain in shadows by the higher ISO. R5 dynamic range at ISO 200 is 12.18EV, which is a full stop lower than the maximum. I’m not sure this is a good tradeoff, given that the same f/stop can be extracted in post without affecting the noise. It’s easy to see how this would be beneficial for jpegs or video, but not for the raw files. Needs further investigation.

Source: Canon EOS R5 - DXOMARK

Consider using Camera Neutral instead. Adobe has its own views on how an image should look.

Nice choice. Solux can be driven to the vicinity of 5500K but only just, see Making a camera profile with DCamProf. It’s not a big deal, but is something to remember when configuring the profile generation.

Bit depth question is a difficult one. On the one hand, 14bit can be argued to be sufficient. On the other, (monochrome) tonality improvement on 16bit is visible, but still is not comparable with analogue print in smoothness. Also, 14bit in camera specs does not mean 16384 discernible levels. R5 sensor only has about 308 levels per channel, meaning about 29M colors as opposed to the theoretical 4 trillions.

Source: Canon EOS R5 - DXOMARK

Yes. However if you are going to build a profile in the future, keep the scanning setup consistent so that the profile would be applicable to the previously scanned images.

Different films use different emulsions, with result being the difference in color response. This response comprises the “film character”, or “the look”. One and the same object shot on different films may be rendered in a slightly different color. When we are applying a film profile, we are not looking to achieve a “realistic” image, or the look of the object in reality, as this isn’t possible. What is possible is to measure the color response of a particular film (superimposed on the response of the scanning equipment) and then apply it to a scanned frame.

Because the color response of different film brands varies, sometimes significantly, mixing and matching of films and profiles is going to give imprecise results. The deviation will typically be visible, but likely not that significant, and can actually be pleasing, just won’t be that a precise match. In any case, applying a non-matching film profile often is way better than keeping the image without color management. Deviations introduced by the scanning equipment can be far larger than the difference between film profiles.

The results will be different, noticeably but not necessarily significantly. Whether the difference will be definitive depends on the scanning goals.

It seems your are talking about areas so dense, that the scanner’s backlight power at maximum is not sufficient for the sensor to detect the values. This should mean the film density exceeds the scanner maximum density specification (which is not unusual for slides). There is no arguing a scanner has a performance limit, beyond which it just can’t do much. Speed of the scanning is a function of the selected scanning resolution. Therefore, since the backlight flow is continuous, the decisive factor is not the duration of the illuminance but its power. If the power is not sufficient to penetrate a given film density, the sensor will not get any data.

So, while multipass and analogue gain do give very real improvements when the film density is within the scanner specification, naturally, they won’t help much when the density is beyond that.

As a matter of fact, the exposure on an Epson scanner using VueScan can be increased to a complete overexposure. This won’t help with higher density images for a different reason, which is the light scatter within the scanner. The flare becomes so uncontrollable, it doesn’t makes sense to scan at such configuration. This doesn’t happen to the same extent with DSLR, but still remains a major quality factor.

Where/how did you get that information?

Source: Canon EOS R5 - DXOMARK

2^8.27 ~= 308. If dxomark data is to be believed, and if I’m interpreting it correctly.

Strange, compared to what I see here:

…and from the same page as you:

You are looking at the dynamic range which is measured in Ev (f/stops, log2). Select the Tonal Range tab on dxomark site. Sorry for not being specific enough before.

The interpretation seems to be correct in terms of what is said in DXOMARK camera sensor testing protocol and scores:

The best image quality metric that correlates with color depth is color sensitivity, which indicates to what degree of subtlety color nuances can be distinguished from one another (and often means a hit or a miss on a pantone palette). Maximum color sensitivity reports in bits the number of colors that the sensor is able to distinguish.

Yet, the chart does look weird, and I’m not sure I quite grasp the difference between the normalized Print and Screen charts on their site, and how the Tonal Range chart correlates with the Color Sensitivity. My statement of 308 levels per channels may be incorrect, but in any case the camera’s capability to distinguish tones is under 10 bits per channel, which is 1024 levels. I can’t substantiate this at the moment though, this was a research I did quite a while ago.

Or maybe it isn’t incorrect after all. Guys over tested R5 and found this (translated by Google):


In the chart above, we can see that for the lowest native sensitivity, the number of tones reaches around 326, so we get an 8.4-bit data record. Regardless of these criteria, the R5 is unfortunately inferior to its competitors. For example, Nikon Z7 got 9 bits, Panasonic S1R 8.7 bits, Sony A7R IV - 8.8 bits. Increasing the sensitivity obviously degrades the tonal range and at ISO 1600 in the EOS we get the values ​​of 7.1 bits, which gives about 135 tonal transitions. With the maximum available ISO of tonal transitions, we only have 16, which is 4 bits.

The difference between 308 and 326 could be due to the testing methodology.

Just ran a test and D+ (highlight tone priority) does meter the image at X, then adjust to X -1EV only if needed.

I know I would much rather pull a shadow darker than push it brighter, especially considering color shifts. In my bracket tests so far, shadow noise when I equalized exposures (- 0 + EV) to match 0EV and then moved further with the shadow slider is visibly superior in the +1 (or more) exposure this way with no discernible differences in mids and highlights. But lab tests would say otherwise, I suspect. For critical single scans, I am using all manual mode in a completely separate setup/light source and a few test shots, etc., taking all of what I have learned here into deep consideration!

Again, quite the education few days for me.

For bulk scanning, my choice/theory involved a few things, all of which were based nearly totally on speed…

  • The noise at ISO 200/400 is functionally not all that different from 100 in practical real world terms.
  • The tonal/DR penalty is real, I understand. But… bulk scanning and then doing more critical stuff after makes this difference here less important.
  • It also gave me the shutter speed advantage I want because of the aforementioned projector fan vibrations!
  • We just can’t have it all, can we! I just want a perfect 100 CRI light, perfect flat field autofocus lens at 1:1 that can scan imperfectly flat film somehow at 2000+ frames per hour providing me a raw file at ISO 100, f5.6, 1/500th, 16bits and 100MP, with perfect color SOOC, hands free, every time without fail y’all! EASY!

It seems likely that you’re correct @nicnilov and I can just set min and max shutter limits to achieve the same purpose without the D+ limitations. More testing! This pushes me more towards to Solux bulbs since they are brighter and I can nullify the ISO 200/400 part of my equasion.

I cannot disable the projector’s fan and its vibrations, at least not yet that I can figure. I did remove the 82V/300W light and installed my own separately powered 12V/7.5W (single point LED) light so it can be on while the projector (fan) can be turned off for in the moment, vibration free scans. Though I lose the ability to advance the slides in this situation and thus bulk scanning becomes tedious, hence wanting to kill the fan entirely.

If I end up with the halogen bulb I will (perhaps!?) want to keep the fan for cooling, but maybe a Solux bulb isn’t so bad compared to the 150/300W bulbs it was designed for! If I stick with my current LED solution, I can truly investigate killing the fan but cannot harm the advancing mechanism. 12v/35W/50W Solux bulbs are going in for testing as soon as I get them.

In any case, the speed at which this can process, hands free, is hard to ignore.

For color and capture, CRI, R9, Lumens, and CBCP (center-beam candle power) measurements all matter. A brighter light is great… but I want to keep my lenses between f4-f8 for sharpness with limited diffraction and not have to use ND filters anywhere in the line.

Such a complicated and fun mess and I will keep saying it - Thank you all for such a lively conversation. I am learning so much about the speed, quality, and time cost compromises that are required!


I will do some testing for sure. And surprisingly DXO says R5 ISO 400 is better than 200 for DR but not for tonal range. So I tested it and 400 compares more favorably to 100 when equalized (+/-2EV for either) than 200 does (+/-1EV for either). So strange. I wish I had the resources ($) to test this all against a few other cameras.

I think this has something to do with Canon’s Dual Pixel technology (dual gain) which is hard to utilize efficiently (requires their software, DPP)…

Also, I am surely letting the perfect be the enemy of the good here.

Thanks for instigating this discussion about colour and colour profiling, very interesting. I’m thinking that you’re well on the way to creating a very good system with which to embark on your task. I’m slightly worried by your hot projector light source though. Solux Halogen bulbs are of course the gold standard but are they future proof? Clearly they’re still on sale but for how much longer I wonder. Nicnilov is absolutely correct to suggest that LEDs and CRI ratings are problematic but it would be great if there actually was an LED light source that would fit the bill. Certainly DT Transitions make one for demanding applications, as seemingly do Negative Supply so it must be possible. It would mean that you wouldn’t need to live with that heat, and that fan!

I’m not sure you really need to keep your shutter speed shorter than 1/125, with a short time delay and a solid setup I get sharpness indistinguishable from flash at 1/2 sec.

There is of course a good thread on light sources on here:

I have no knowledge of this company but they seem to be producing some interesting products.

I currently use a nice LED that runs cool enough to touch! The 35/50W Solux versions will be hotter but slides are never in for more than a minute or so max, but usually mere seconds. These both pale in comparison to the 300W bulb it typically works with!

As for shutter speeds, 1/125 is ok, but 1/250 or more is fractionally (but visibly) better so that is what I am going with currently.

I think I can adjust my light source to be more focused on the CBCP the bulb is able to do, but I need to get some scanning done first.

I’d be interested to see what Negative Supply is using honestly, because I can DIY-solder basic lights with the best of them! Ha!

Thanks for the links!

Well, I appreciate that you’re sharing all this information so I hope you don’t mind me suggesting that if there is a difference in sharpness between 1/125 and 1/250 then that might be an area to look at. On the face of it that would suggest to me that the camera support isn’t sufficiently stable and is allowing some kind of vibration to creep in.