Noise vs. Grain

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Noise vs. Grain

Postby Ganesh H Shankar » Sat Apr 25, 2015 9:51 pm

In past we might have interchangeably used the word grain and noise. Actually they are very different. The 'grain' came from film/slides days(film grain). The noise came from digital world (sensor noise). What is the difference? To illustrate this I went back to my slide collections. I took a scanned slide and cropped a 1000x1000 pixel plain crop from slide and another 1000x1000 pixel crop from a digital file. Here they go!

Please see this on a large display (preferably a calibrated display (matt preferred), not on your cell phone!) to appreciate the subtle differences.

First, Slide/Film Grain

grain.jpg
grain.jpg (457.07 KiB) Viewed 7195 times


Now, Digital (CCD/CMOS sensor) Noise

noise_1.jpg
noise_1.jpg (619.47 KiB) Viewed 7195 times


Do you see the difference?

The point to note here is -

1. Grain has larger random structures - this is caused by lumps of silver halide deposits on the film/slide, which gets unevenly exposed causing granular tiny lumps. Different films/slides had/have different structures. Some films are very fine (like the one I shared above, which is Velvia 50 ISO slide film crop) and some a little more coarser. While excessive grain is not desirable a little bit of it often results in very pleasing image and gives depth to an image. In the digital world it is tough to get this subtle grains which brings life to the final output, mostly to prints (and as we have seen here at CNP it works for web images too).

2. In contrast, sensor noise is uniform and is made up of finer specs which are dimensionless! Sensor noise is not very desirable. We often try to get rid of it (using different noise removal softwares).

Let us try an experiment here. What I will try to do next is, overlaying slide grain and digital noise on an otherwise clean digital image. Let me share the clean image first.

A cleaner sample image (1000x1000 pixels)

img_with_no_grain.jpg
img_with_no_grain.jpg (181.55 KiB) Viewed 7195 times


Now let me overlay the slide grain on this clean image. Let us see how it looks,

Image with Slide Grain (digital image + slide grain)

img_with_grain.jpg
img_with_grain.jpg (384.95 KiB) Viewed 7195 times


Now, the same image with digital noise overlaid (digital image + digital noise)

img_with_noise.jpg
img_with_noise.jpg (459.52 KiB) Viewed 7195 times


Which one you prefer?

I definitely prefer slide grain! I love the subtle (emotional) nuances/depth the random grains create.

Now, let us look at the same image with software simulated grain (using Nik's simulated grain)

img_with_sw_grain.jpg
img_with_sw_grain.jpg (402.38 KiB) Viewed 7195 times


I think this is better than digital noise but the not as beautiful as slide grain! What you think?

Here is another emulated grains (of Ilford HP5 plus film)

img_with_no_ilford.jpg
img_with_no_ilford.jpg (318.25 KiB) Viewed 7089 times


Hope this is useful, for those who never used slide/film.

Next time when we talk about 'noise' or 'grain' we have a reference!!
Ganesh H. Shankar
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Re: Noise vs. Grain

Postby kalyan » Sun Apr 26, 2015 12:14 am

Ganesh, I totally agree with you. But one point we must note is this: Grain/noise actually adds to the image in black and white images. Traditional BW film also had high contrasts and lot of grain. But in color photographs, I do not know if adds that much character to an image.
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Re: Noise vs. Grain

Postby Ganesh H Shankar » Sun Apr 26, 2015 8:12 am

Kalyan, I think grain seem to trigger some dimension of time, some sense of age (my personal and subjective take). Probably it works better when time is an implied dimension of an image. I think grain might enhance a faded color image of an old building. However, it might not help much for the color image of a subject in nature since the mother nature don't seem to get aged :) But then why it helps images of nature in B&W? I think, 'nature' is kind of half lost in pure B&W images of nature (due to loss of color). However, it brings in other dimensions of human life/emotions having some trace of time in them.
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Re: Noise vs. Grain

Postby Ganesh H Shankar » Sun Apr 26, 2015 9:14 am

On software simulation of the grains using softwares like Photoshop or Nik's SilverFX I think the final result may not be very close what we get in real film/slide grains. The issue, I think, is modelling of grain in software is not just simulation of varied sizes of dots. It might need subtle light modelling around those tiny lumps of simulated silver halide crystals. Probably the best bet is emulation which would need scanned digital image of those real slide/film grain samples and overlaying them on the image (like what I did here).
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Re: Noise vs. Grain

Postby Madhav Jois » Tue Apr 28, 2015 11:10 pm

Thanks for sharing this info Ganesh! Really helpful to get some perspective on noise. Film grain is very subtle compared to digital noise. Wonder what was the film ISO rating and how would higher ISO grain be like. I cant tell any difference between the simulated noise (using Nik software) and the super-imposed slide grain.
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Re: Noise vs. Grain

Postby Ganesh H Shankar » Sat Apr 18, 2020 9:40 pm

5 years later, a related discussion and link to True Grain in this image post.

image_id: 17000
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