As a part of my 30 Days with the Fuji X-T2 project, I’ve been digging into Fuji’s new(ish) Acros film simulation. It was released with the X-Pro 2 earlier this year, so there have been a few articles/reviews written about its characteristics. I don’t own the X-Pro 2, though, so I’ve only started playing with Acros recently and I found that the posts out there weren’t answering all my questions. In particular, I was interested in Acros’s sensitivity to colors compared to the standard Monochrome setting. I couldn’t find any posts that covered the topic, so I set out to do some comparisons myself!
Before I get into all the comparisons I did (which go a bit beyond simply looking at color sensitivities), I want to give credit to the very informative post on Acros on the Fujifilm-X website. It answered a lot of questions I had about the details of the film simulation, and I’ll be referring to some of the points on this page throughout this post.
Alright, on to the comparisons!
The first thing I wanted to investigate was the color sensitivity of Acros vs. Monochrome. The curiosity driving this comparison stemmed from the fact that Acros film has some unique color sensitivity properties and I was curious to see if these translated to the digital simulation.
I’ve been shooting film quite a bit lately, and in my research on black and white film stocks I kept hearing the term orthopanchromatic thrown around with respect to Acros. I did a little research to figure out what the heck that meant, and it turns out this term refers to films that have low sensitivity to certain wavelengths of light (colors). I mentioned in one of my 30 Days posts that most black and white films render colors of different light intensities as similar shades of grey, but orthopanchromatic films are obviously an exception. And Acros falls into the orthopanchromatic category.
The image below is courtesy of the Fujifilm Acros data sheet. It shows the relative sensitivity of Acros to light of certain wavelengths/color bands.
For those that don’t know the relationship between wavelengths and color by heart (tsk tsk :P), this chart might help.
Combining these two images, we can see that Acros has a pretty average sensitivity to most color bands, which means that it will render each of those colors similar shades of grey for a fixed light intensity. However, above about 625 nanometers the sensitivity falls off a cliff. This means that from orange-red to dark red, Acros will have pretty much no sensitivity. This will in turn cause the colors to be rendered as very dark compared to the rest of the image (again, assuming a fixed light intensity).
If this phenomenon exists in the digital film simulation, the value of using a red filter would be negated. The effects of a red filter are most prominently to brighten reds and darken blues/violets. The blues/violets would still be darkened when using a red filter with Acros, but some of the point of the lower sensitivity to reds would be negated. As someone who loves using a red filter on my images, I was very curious to see if Fuji baked this orthopanchromatic nature of the Acros film stock into its film simulation. If they did, it might cause me to simply use the Monochrome + Red Filter combination rather than the new Acros + Red Filter setting.
I couldn’t find anyone who had investigated this, and Fuji didn’t seem to be releasing any information on the subject, so I decided to make some comparisons myself. The test image we’ll be looking at was shot in downtown Lincoln, and it has some sections of blue, red, and orange, making it a great image for this sort of color comparison. It was shot with the X-T2 and the XF 35mm f/2 lens, and the settings were 1/420 seconds at f/8.0 and ISO 200. Here’s the color image, which was produced by importing the RAW image into Lightroom and exporting to a JPEG with the Camera Calibration Profile set to Adobe Standard.
First, we’ll hone in on the red umbrellas and compare the Acros and Monochrome JPEGs produced by the Fuji X-T2’s RAW converter. If Fuji built the orthopanchromatic nature of Acros into the Acros film simulation, we’d expect the Acros JPEG to have very dark umbrellas as compared to the (presumably) more neutral Monochrome JPEG. Both images were produced by the Fuji X-T2 RAW converter with no adjustments made to highlight tone, shadow tone, sharpening, or noise reduction. They’re viewed at 800% in order to more easily compare the pixels’ tonality.
At least to my eye, there’s no difference in the overall tonality of the reds. If there was any meaningful difference that would cause me to want to use the Monochrome + Red Filter setting rather than the Acros + Red Filter setting, I’d expect to see it here. As such, I think it’s safe to say that Fuji didn’t incorporate the low sensitivity to reds of Acros into the Acros film simulation.
While there’s no apparent difference in the sensitivity to reds in the above comparison, there are certainly some differences in the tonality of certain portions of the shot. The Monochrome shot looks smoother and the Acros shot looks more noisy/contrasty.
The reason for seems to be the unique tonal curve that Acros has. The following quote is from the Fujifilm article that I mentioned at the top of the post:
This tonality curve, specifically designed for ACROS, has a distinguishable characteristic compared to the existing “B&W”. First, from middle to the highest, the tonality curve is rather hard. By doing so, the detail stands out, and therefore the image appears clean and sharp. It doesn’t not mean, however, that it gets overexposed easily. The highest input and output remains at the same level. The dynamic range stays the same.
This totally lines up with what we saw in the comparison above. Pixels that are slightly brighter than middle grey get lightened a bit in Acros and pixels that are slightly darker than middle grey get darkened a bit in Acros. The brightest and darkest tones are more or less left alone. This creates some micro contrast, particularly around the edges.
The following comparison, taken from a portion of the brick wall in the image above, shows the differences a bit more clearly. Again, the image is shown at very high magnification simply to make it easier to see the tonality of individual pixels. Also, WordPress’s image compression makes this comparison a bit tough to see, so feel free to click on the image to open it full size in a new tab.
It’s important to point out that there may be factors other than the special tonality curve at play here. Even though the noise reduction was set to zero on both images, Fuji notes that the Acros mode has a completely different noise reduction algorithm than other modes. And even if the noise reduction is set to zero, the Fuji RAW converter is still applying some noise reduction. It is likely that some of the added micro contrast in the Acros image is due to less default noise reduction. Fuji also mentions that they turn this “noise into grain-like texture”, so there’s probably more going on here other than simply tweaking the amount of noise reduction. Specifically, Fuji suggests that the noise/grain produced by the RAW converter in the Acros mode varies by luminosity, with the highlights receiving more noise reduction and the shadows receiving less noise reduction (and thus more “grain” and perhaps more micro contrast):
We developed it from the core of the image file to achieve a very complex and natural like grain expression. Optimal and different grain expressions are added to highlight and low light areas. You would not find unnatural dotted graininess in the highlight areas just like how the monochrome film behaves. In the low light area, you would see the graininess just like how it would appear with the monochrome film. There are undulating grain within the picture. And it adds depth like no other.
JPEG vs. RAW
The last thing I wanted to investigate was how well the Adobe Camera Calibration Profile for Acros mirrored the JPEGs produced by the in-camera Fuji RAW converter. Based on the quotes above, we’d expect there to be some pretty significant differences, as the Fuji RAW converter appears to have some more sophisticated algorithms that would be difficult for Adobe to implement. For most film simulation modes, the Adobe Camera Calibration Profiles do a pretty good job of emulating the Fuji JPEGs. The comparisons I did between the RAW and JPEG versions of this image on the Monochrome mode reinforced this view, as I could only see minor differences between the two files.
The following comparison shows the JPEG produced by the in-camera Fuji RAW converter set to the Acros setting against the image produced by the Adobe RAW Camera Calibration Profile set to Acros. The in-camera RAW converter settings for the JPEG are as described above, and no adjustments are made to the RAW in Lightroom aside from setting the Camera Calibration Profile.
There are some pretty obvious differences here when viewed at very high magnification. The micro contrast is obviously much more significant in the JPEG. There are a lot of other variables at play here, of course. For example, as mentioned earlier, the Fuji RAW converter is applying some noise reduction and some sharpening, whereas the RAW file hasn’t received any of this treatment other than the Lightroom defaults. So while this certainly isn’t a scientific comparison, I think it’s fair to say there are some significant differences between the JPEGs produced by the Fuji and the Adobe RAW Profile. Since this file was shot at ISO 200, there’s not much of the grain-like effect Fuji alludes to, but I think it’s a safe assumption that at higher ISOs the difference between the JPEG and RAW files will be more significant.
All that said, if you view the JPEG and RAW files side-by-side at fairly small sizes (e.g., 1000 pixels wide), it’s pretty tough to tell any difference (at least for this image).
For me, the most important takeaway of this exercise is that the Fuji film simulation isn’t orthopanchromatic. It appears to have similar color sensitivity as the Monochrome setting. This means that I can shoot Acros + Red Filter to my heart’s content without worrying about “undoing” some of the uniqueness of Acros.
The other takeaway that seems pretty significant is that the JPEGs produced by the Fuji will have more contrast in the midtones and will thus likely have higher perceived sharpness as compared to either Monochrome JPEGs or Adobe RAWs. This combination of increased perceived sharpness with the grain-like effect could create some interesting depth. This is probably enough to keep me shooting RAW + Acros JPEG for quite some time. 🙂
I hope you enjoyed these comparisons, and thanks for reading! If you have any questions on anything I covered or if you have ideas for future comparisons, please let me know in the comments section below!