The rabbit hole of adding grain to digital photos

There are image-software companies whose specialties include careful emulation of grain. I don't use them, but plugins like https://nikcollection.dxo.com/silver-efex-pro/ are intended for that very purpose.

For example, Kodak make 'traditional' and 'T-grain' versions of their B&W film (I believe the 'T-grain' style has the grains stacked vertically rather than horizontally, allowing for more light sensitivity but smaller visible grain). So, if you want ISO 400 B&W film, Kodak will sell you TriX for traditional grain, and Tmax for modern 'T-grain'.

The article discusses grain visibility in shadows vs mid tone and highlignts, and suggests that grain is visible across the entire image. This isn't true. The process of exposing film converts silver halide to silver granules where the light has been captured, so in shadows, the grain is purely silver halide which is removed by the fix step when developing the film, leaving only the film base. So, unexposed film (shadows) have no grain, highlights have all the grain. This is the opposite of digital, where if anything, noise is most visible in the shadows, whilst on film, shadows are pure black with no noise (from grain).

Another thing, different printing processes cause the grain to be more or less visible. Traditional enlargers use collimated light which produces very sharp images, but accentuates dust and film grain. This fell out of favour to be replaced with diffuse light, which drops the sharpness a little, but is much more forgiving.

> Noise, by nature, is digital so it is all square-shaped, like a pixel, and it’s uniform in nature because pixels are just a grid of little, tiny squares. So when you look very closely you can easily tell that noise and grain are two very different things with grain achieving actual randomness of size and positioning while noise is just a table of black, white, and grey squares.

edit: And calling film grain "organic" is a bit of a stretch, it's silver halide crystals.

And yes, ImageMagick can be a rabbit hole of possibilities too. But now I'm tempted to try it … tomorrow.

I almost always add a subtle amount of "grain" with LR when developing photos. It looks pleasant and seems to add a sense of coherency to an image. I find that in many cases where details are lost to aggressive NR or otherwise simply not present, grain can make it easier to "see" the missing detail... as with most things, the optimal amount of noise is not zero.

Of course that results in digital noise, which is not visually equivalent but is an artifact of your actual medium.

If you don't like the digital look, you can still use this method, but develop the image twice, one timein monochrome with contrast and brightness in mind.. Then another photo with color and saturation in mind..

Then you cheat and do a Gaussian blur on the color photo that is strong enough that the digital noise diminishes to an acceptable level.. then you overlay the blurred color image on top of the sharp black/white image with saturation from the color image being used.

This is a hack, and can also be used if you shot some color picture in adverse conditions and want both colors and sharpness.

http://www.cinegrain.com/

I first learned about this in vision, but it's generally true. https://www.electronicsweekly.com/news/research-news/add-noi...

My best guess is that besides grain digital photos have a different dynamic range. The whole stack from silicon sensor, raw processing, etc, including screen manufacturing is trying to get to "real" images, in the sense that it is similar to what the human eye of the photographer saw in site. Film also tried to do the same, yet, I guess there are more characteristics than we can simulate with math.

I bet if someone gathers enough data an AI based plugin might get closer to the actual film look rather hand-coded math based plugins will be able to.

They don't blur like a gaussian filter, they have two separate plates, one that spreads light horizontally and the other vertically, ideally by about 1.0 pixel radius in each direction. This results in "square-like" artifacts, especially if the filters spread by more than 1.5 pixels.

The artifacts are most noticeable in astronomy where there is a dramatic difference between the appearance of star fields with and without anti-aliasing filters.

I don't know how this effect works against film simulation but it probably doesn't help. If they are going to start with Gaussian blur anyway, then using a camera with the antis-aliasing filters removed might help.

For computers and Lightroom/Photoshop you have stuff like Replichrone to help.

    10 PRINT "Is your name Stanley Kubrick? (Y/N)"
    20 A$=GET$();
    30 IF A$ <> "Y" THEN PRINT "Don't do that"

VFX pipelines have dealt with actual film grain for a very long time (for about as long as there has been telecine/scanning) - and dealing with moving image grain-wise gives more perspective than doing that on stills. A few interesting items to consider if you ever want to dive into that domain:

* There is a difference whether you want to "add film look" or you need to integrate digital images into an existing scanned film image. The latter is harder because "your" grain has to match "their" grain!

* Grain in film is different to digital noise not because the digital noise is pixel based, but because the digital noise is a property of the sensor. Therefore digital noise will produce clusters of pixels or single pixels which run "hotter" or "colder" on every image shot. Some cameras are much worse with this (noise patterns are extremely regular between frames), some are better. Film grain are physical particles spread on a medium, which gives them a great property of incredibly high entropy

* Consequently, when you want to increase detail you often can do "temporal averaging" - take multiple frames of the same subject under same conditions and average the signal across them. This removes virtually 100% of the film grain and allows you to produce a good "grain plate" which can then be re-added to your source material or digital material. Doing the same with digital noise of the sensor won't work so well, because (see above) a sensor inherently has some noisier elements than the rest, and they stay in the same position. Some digital cameras tried to innovate in this space by moving the sensor laterally during shooting, exactly so that you can later do temporal averaging to de-noise (unlike blurring temporal denoising is theoretically losless). And yes - temporal denoisingby averaging is also way better than the modern ML-based denoising (and cheaper computationally).

* Grain - as well as digital noise - have varying response per color channel, as well as varying sizes. For grain this is because of the different dyes used to capture different parts of the spectrum, as well as due to "demasking" of the negative. The channel split depends on the film stock / type of sensor, how far the exposure is pushed - but also on the color management pipeline applied throughout the process. Sometimes your response per channel is actually "roughly" YUV instead of roughly RGB

* Noise and grain will be affected by chroma subsampling - your "color" channels having less resolution than luminance channels. If you are working on material which has already been heavily compressed (like smartphone photos, lol) you need to take that into account

* This might seem unimportant, but the _size_ of the grain is a great hint to the brain that "this was shot on mid-format" vs. "this was shot on 8mm" vs. "this was shot on 35mm". For proper artistic effect it is always a good idea to take this into account.

There has been a lot of work done in the VFX world to provide for at least some "recorded" or analyzed grain sampling at least for widely used moving picture film stocks.

Oh, and last but not least - you can throw rotten eggs at me, but "film look" is overrated, just as "no photoshop used" is overrated. I'll see myself out :-D