Pixels, not grains – Why RA4 paper is ‘digital’, and why this matters (not?)

Look at the back print of some papers, such as FUJIFILM’s Crystal Archive Supreme HD, and the word ‘digital’ features prominently. Indeed, I’ve been told that current Fuji RA4 color papers are exclusively intended for digital exposure. But does that mean we can’t use them anymore for optical enlargements?

To an extent, the question is a bit of an academic one. I’ve been printing on FUJIFILM RA4 papers for a few years, and have printed on Kodak Royal ‘digital’ paper as well for a while. Stacked in boxes, I’ve got more than enough proof to show that it works – you can make color prints on these digital papers, with normal dichroic filter enlargers as well as LED contraptions. One caveat on the latter is that some care is needed in selecting proper LED wavelengths, but that’s an issue I’ve discussed at some length already.

But in principle, light is light, right? And isn’t that true, regardless of how we create and manipulate this light? Does it matter whether we:
(1) take a white light source and use dichroic filters to selectively cut certain bandwidths, then shine the light through a negative,
(2) take red, green and blue LEDs (of appropriate wavelengths) and vary their intensities, and also shine this light through a negative,
(3) use red, green and blue semiconductor lasers (again, of appropriate wavelengths), modulate these lasers digitally and scan them across the paper to expose an image without any negative involved?

You guessed it: it does matter. And the reason has nothing to do with these light sources per se. In principle, they’re all usable. The only real difference is that with the 3rd approach, we can perform all sorts of corrections and adjustments that we can’t do, or only with much difficulty using a color negative. And it so happens that today’s papers require such adjustments.

Back print of Crystal Archive Supreme HD paper: it’s very…digital.

So, how come? Previously, when FUJIFILM made a color paper, each color layer was in fact made from two light-sensitive emulsions. Hence, there used to be six light-sensitive emulsions used in an RA4 paper: three sets of two emulsions. Together, these sets were tailored in such a way to create nearly perfectly tracking Cyan, Magenta and Yellow dye images. By this tracking, I mean that the response curves of the color layers are nicely parallel, which prevents color crossover.

Schematic representation of well-tracking response curves in to red, green and blue light of the three color emulsion layers. The curves are slightly offset from each other as they would overlap perfectly in an ideal situation. Perfect tracking means that there will be no color crossover in the image.

Two things happened, however. Firstly, digital exposure systems like Durst Lambda and OcĂ© Lightjet came along. These expose RA4 papers with digitally modulated lasers. Given this digital control, an inherent match between the response of the RA4 paper and a color negative is no longer necessary – there is no negative anymore, after all. Moreover, even if the color response curves of the paper don’t track very well anymore, this can be corrected in the digital exposure, and such corrections can quite simply be embedded into an ICC profile so they’re always applied automatically to every print being made. Simply put: color RA4 paper just doesn’t have to be quite as good anymore in terms of crossover performance than it used to. Other parameters such as hue purity and chroma are still very essential, as is batch-to-batch consistency, aging properties etc. But crossover is just less of a concern because it can be ‘corrected away’ digitally.

The second thing that happened has always been happening, and that’s a continuous pressure to reduce costs. RA4 paper is a volume market and a commodity, and all sorts of market pressures, including competition between Kodak and FUJIFILM (but not limited to this) constantly press engineers to conceive of ways to get similar performance at lower costs. Given the digital story above, one possibility a number of years ago was to reduce the number of color emulsions in each color layer from two to one. The technical cost of this intervention was that color layer tracking was no longer quite as perfect – in fact, it has become quite compromised by the old standards before the advent of digital. The economic cost, however, was worthwhile. And the technical drawback actually wasn’t much of a drawback at all, because the flexibility of digital exposure could still achieve the same overall performance of the exposure-paper system.

The net result is that if you look at the color response curves of these papers today, they look more like this:

Schematic representation of what the color response curves of RA4 color paper look like today. Note how the green curve (forming the magenta dye image in the print) no longer tracks the other two. Vertical axis represents print density, from dmin (bottom) to dmax (top).

The main difference is that the steepness (gamma) of the green/magenta layer curve is no longer in line with the other layers. I think the toe and shoulder behavior are also different, but I’m not entirely sure on this. As said before, for digital exposure systems, this is not a problem. The ‘new’ papers have been in use for years already, ICC profiles are available from FUJIFILM and it’s evidently possible to make fantastic prints on these papers – at least when used as intended by the manufacturer.

For optical printers, like myself, this means that these papers will exhibit a magenta/green crossover. Since it is an actual crossover, there’s no adjustment of light source wavelengths, filtration settings etc. that will make the problem go away. The only way to work around this is to create a color correction mask that brings the curves back in line with each other. Personally, I’m not quite prepared to go that far. Color masking, especially to get it right, requires extensive calibration using panchromatic film, and for me, that’s a cost-prohibitive and overall unattractive (i.e. excessively boring/tedious) endeavor.

So does this mean that this is the end of the road for optical color RA4 enlargement? Well, yes, and no. Yes, in the sense that the current generation of FUJIFILM papers simply is no longer suitable for optical enlargements with high requirements on excellent color accuracy. It’s still fine for this in its intended use, i.e. in digital exposure systems – evidently. It’s also conceivable to make these papers work magnificently with supplementary color masking, if one is willing to face the effort and costs involved of doing so.

And there’s the slight possibility that not all papers in the market have undergone this change. For instance, Kodak Alaris still explicitly mentions optical enlargement as a possibility for their papers. At least, in the datasheet that Google retrieved, which dates back to 2017. This still leaves a number of unanswered questions: is this information still accurate? Now that Endura paper manufacturing is in the hands of Sinopromise and Kodak has no direct involvement in it anymore, are they still maintaining this optical printing compatibility? And this compatibility, how good has it been over the past years anyway? The fact that you can expose a paper under an enlarger doesn’t mean its color rendition will be dead-accurate – and the Kodak datasheet isn’t specific on the actual performance.

Another, and more relevant source of light at the end of the tunnel, is that for all intents and purposes, it’s evidently still possible to make very nice prints even on FUJIFILM ‘digital’ papers using an optical enlarger. I’ve burned several rolls of their ‘new’ papers, and the prints are really nice. Are they perfect? Well, evidently not – it’s impossible that they would be! But they’re very nice as they are, satisfying to make, and they look perfectly natural. The crossover that inevitably is there, is not necessarily disastrous. And for me, that’s more than enough reason to keep printing RA4 color in the darkroom from time to time.

19 thoughts on “Pixels, not grains – Why RA4 paper is ‘digital’, and why this matters (not?)”

  1. Color Management
    SUPRA ENDURA VC Digital Paper is optimized for printing in both internal and external color-managed, short exposure, digital workflows. Many digital printers have color-management capability built into their software.
    SUPRA ENDURA VC Digital Paper is fully compatible with these printers.
    Optical Printing
    This paper can be printed optically. The image will be high in contrast and, if balanced on flesh tones, the neutrals will appear cyan. [2009] e4042 situation pub.

    1. Richard, many thanks for supplementing this information! The comment on skin balancing producing cyan neutrals suggests that this paper is no longer optimized for classic enlarger use, although it does produce a presentable image alright – correct?

  2. Supra Endura VC digital was designated for such printers as the ZBE (LED) or OCEs and Polielettronica(Laser).
    Yes, balance to a perfect “commercial” grey card and skin would be called ruddy, or beefy in the dark tones. This was noticeable enough to be mentioned by Kodak Tech.
    In practice, using a common Dichroic head, this would be around 15CC difference. Probably good enough. More likely you pick your preference and print to that.

    Around 2011 Kodak paper datasheets stopped noting that caution.
    The current owner of the Kodak color paper (Sino Promise) is a major seller of digital labs and supplies.

    Anyone using any of the current printing machines is provided digital targets, and guidance for setting start points. Also, the machines have very complete “balancing” modes. Much better than in the days of on-easel closed loop systems.

    1. Richard, many thanks once more – these are valuable reflections indeed. You mention Supra Endura VC Digital specifically – I’m not very well aware of the Kodak Endura lineup and any changes it might have gone through. But has there been a true enlarger-compatible Endura paper in recent years, at all?

      Btw, a 15CC dichroic filter difference is pretty visible, at least if you know you’re looking at it. I do recognize the ‘ruddy/beefy’ skin tones, btw. I always thought they had a lot to do with the expired Superia 200 I’ve shot and printed a lot of, but I got the same from e.g. fresh Kodak ProImage film printed onto Fuji RA4 paper. With what I know now, it wouldn’t surprise me if I’m looking at the same effect as you’re describing. Sounds like I’ll have to do some more testing, and also some more querying of Fuji.

      As to the ZBE Chromira LED systems – do you happen to know if these are conceptually the same kind of LED print heads consisting of a number of staggered strip-bars that we also find in some ‘laser’ printers, such as those made by the Fuji-Xerox partnership? I presume that most RA4 exposure systems probably use semiconductor lasers currently and I recently hypothesized the existence of LED-bar exposure units, but I never looked into the matter.

      Thanks again, I really value your input!

      1. ZBE: patents and brochure
        If you go through the patents, you will find flow chart for normalization[6,452,696B1] routine. Jim Browning * Zac Bogart.


        U.S. Pat. No. 3,988,742 describes using light emitting diodes (LED’s) and fiber optic tubes to deliver light to the photosensitive material. Applications of this technology have included typesetting and the generation of lithographic films for printing. In these applications, each LED is typically coupled to the input end of a fiber optic tube and the output ends of multiple tubes are arranged in a linear array. As photosensitive material is transported past the linear array, a digital controller energizes the LED’s to form a latent image on the photosensitive material. This process is described in U.S. Pat. Nos. 3,832,488 and 4,000,495 and 5,093,682.
        …Continuous tone images are predominately comprised of intermediate tonal values of color or gray tones. The formation of high quality continuous tone images by multiple light sources requires that the sources be precisely matched. Failure to match the light sources, at all useable light levels, will typically produce unwanted lines or artifacts in the printed image. U.S. Pat. No. 3,988,742 generally recognizes the need for normalization of light sources to minimize mismatches.

        user guide:

  3. Koraks, just awesome that you a sharing so much here on blog. There is a chance someone finds these much better (well as long as you maintain the server), but anycase. Great publishing. When you have enough blog posts, consider publishing an ebook / real book / pdf of your articles too.

    1. Jouni, thanks for your kind words and valuable suggestion! A book or similar would allow for a more consistent and structured approach, so it’s definitely worthwhile. I’ll certainly keep it in mind! Also, I intend to keep this domain and website online for as long as it’s humanly possible. The domain I’ve kept afloat for over a decade already, and the old website hosted on it (which is embarrassing in many ways…) I also keep up just because there are links here and there that point to it. Everyone dislikes broken links! So I’m committed to keeping this information available!

      Congrats also on your own blog (http://blog.vedostuu.fi/) – you offer very relevant reflections on the meaningfulness of photography. Very worthwhile and I recommend people to have a good look at your articles!

  4. I appreciate these posts, as it gives me plenty of food for thought on how much effort to expend on recommissioning my Thermaphot ACP 505 for RA-4 printing via optical exposure, i.e it sounds like I may be better off concentrating on my scanner technique and workflow. In the past I had good results with Kodak Supra Endura paper, a long discontinued product, manufactured at the Kodak facility in Harrow, England.

    1. Tom, thanks for reaching out! That Thermaphot is a nice piece of kit; be sure to go back and use it. Don’t let yourself be held back with what ‘in theory’ might not work the way it did before. Most of the color prints I’ve made are on papers that are optimized for digital. We can still make great prints this way, notwithstanding the fact that the paper is capable of even more than what we can pull out of it in the darkroom. Of course, scanning is also a useful competence. One doesn’t get in the way of the other!

      Btw, lovely work on your website. It would be great to see it in print – all the more reason to keep printing!

  5. As long as Fuji Crystal Archive DP II’s specsheet doesn’t lie, the response curves of this paper should be pretty tight. Only cyan (red-sensitive) layer has very slightly lower steepness (less contrasty), but question is if the difference is noticeable.
    But if we look on specsheets of the print films, they are also not innocent. Both Fuji and Kodak films show slightly less steep cyan curve (again red-sensitive layer).
    So is it really the paper only, what is cost-cut? Or maybe the paper nor film is cost-cut and but it’s maybe some unavoidable inherent property?

    1. Well Ivan, the first thing I did when I was shown the curve I recreated in my article was go and check some datasheets of the Fuji papers. The problem is that at least in the present set of datasheets on the originalphotopaper.com website, no H/D curves are provided. See e.g. here: https://www.originalphotopaper.com/wp-content/uploads/2022/07/Fujicolor-Crystal-Archive-Paper-Type-DPII_AF3-0212E5.pdf. Furthermore, I’ve so far not been able to find ‘pre’ and ‘post’ datasheets that allow for a solid comparison. Note also that curves in datasheets (if present in the first place!) often have unspecified axes scales, making it impossible to accurately interpret their meaning. Finally, without going into details too much at this point: what I report on in this blog traces back pretty directly to the source of the material. And yes, it really has been a change – actually many changes over the years, and they’re generally all aimed at cost-cutting. The H/D example plot I show on the blog I recreated based on the plot I’ve seen myself, and the source and nature of that information was extremely compelling.

      1. Yes, you are right, in recent datasheet of Fuji CA DP II there’s no H/D curve anymore. Maybe for a reason? But my datasheet stored in my PC has the curve. It explicitly doesn’t tell a date. But I looked in PDF properties now and it says creation date 2005. Not uptodate anymore, so things can be really different now. But it says Fuji CA Digital Paper II suited for laser digital printers like Fuji Frontier, no mention of possibility of optical printing. Here is at least pic of the Curve: https://i.imgur.com/odfK2o9.png

        1. Ivan, that’s great! Thanks for posting that plot. It looks very similar to plots that can still be found in some Endura datasheets – but those are also datasheets from the same era, IIRC. One thing I want to check still is how these plots relate exactly to the one I saw and recreated for this blog. I hope I’ll be in a position to further pursue this.

          1. But the endura datasheet of 2017 you linked in your article has quite different curve for red sensitive layer than Fuji CA – it is tiny bit steeper than other two. This gives a hint that this Endura should be more suited for optical printing, because, as I mentioned, the cyan curves of the films tend to be less steep than the other two. This means that Endura cyan layer compensates less steep cyan in the film. On the other hand Fuji CA DP II cyan curve is less steep, which with connection with less steep cyan curve on the film gives even more less steep cyan result in the print. I hope I am still comprehensive ( :
            Here is for example Fuji C200 film plot, where you can see slightly less steep cyan layer. https://i.imgur.com/GrDgc5u.png

          2. Yet another information – I found in my PC another specsheet for Fuji CA DP II, version 2012. It still shows H/D curve and is the same like the one from 2005 I posted. So this make it closer to hope that recent Fuji CA DP II curve is moreless the same.

          3. Ivan, possibly, but I do note that DPII is specifically indicated by Fuji to be ‘digital only’, just like Maxima, Velvet and the other ‘professional’ papers. Only their ‘Sharing’ papers (which are the amateur emulsions) still list ‘analog enlargement’ as a possibility, although I have to take that with a grain of salt given the information I obtained apart from the datasheets. In any case, I’d still like to check in other ways the (in)compatibility of RA4 papers with optical enlargement of C41 film.

            As to your comments on the film curves: they are likely relevant, but there’s one thing I’d like to point out. When enlarging film, it’s not just the spectral response of the film, but also (and more so) the nature of the dye image. So you’d have to include the dye absorption curves (conveniently also present in your snippets) in the analysis to determine how well a paper and a negative are matched. I have not done this exercise; if you’re game, it might be fun to see how far you could get with the plots in the datasheets. At first glance they’re quite similar to each other across different C41 films, but I’m sure there are plenty subtle differences I have never really noticed!

          4. I only wanted to point out that you cannot omit from the equation possible disbalance in gammas of the color components of the film. If the negative itself is already crossed over, you will not get the balanced print even if your paper is perfect.
            What I am wondering is, if it would be possible to control gammas in paper or film layers in desirable way by intervention into development process. For instance to compensate the cyan layer steep in the Fuji paper.
            To check the paper should be relatively easy – to expose grey scale onto the paper, then scan the print and search for some difference in hue between the grey steps…

            Spectral match of the film and paper is also very important, but spectral unmatch will not induce a crossover in the print. It will affect purity and saturation of the colors.

          5. Certainly so; it’s hard to get a good print from a flawed negative. As to modifying the development process: it should be possible, but I doubt it’s feasible to do with the kind of exacting control you’d need. For instance, to address the green/magenta issue this blog post mentions, you’d have to deliberately modify the gamma of the magenta-forming layers in the film, which happen to be the middle image-forming layers in the stack. Any means you might use to modify their gamma would easily spill over to the yellow- and cyan-forming layers as well – especially the latter. Perhaps some subtle nudging of curves is possible, but it’ll have to be subtle before you start getting unintended side effects in different laters.
            I’ve messed with this a little bit at some point when I was trying to coax Vision3 50D film into playing nice with RA4 paper. I specifically tried to use pH as a variable to induce a different crossover behavior to see if this got me any closer to curves that match what RA4 paper liked to see. To my surprise, even pretty dramatic changes in pH didn’t do all that much to crossover behavior. I did get a color shift, and of course the overall gamma changed (which I could compensate for by adjusting development time), but the typical crossed over prints didn’t change appreciable and/or in the desired direction. This makes me skeptical if it’s a feasible route.
            Of course, I only looked into pH very briefly and did not try different approaches. I imagine there are many other factors one could try and leverage. Interesting experiments, for sure, but not ones I’m currently planning actively – certainly not in the light of the present costs of C41 film.

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