Discussion on adding Noise to digital images:

What is Film Grain?

This is a topic that has come up quite frequently in recent months. People keep asking if either they should add some grain to their digital images or not and if yes, what is the best way to achieve this?

I get it that some people do not like adding grain to their images but there are a lot of Photographers and Digital Artists that do. So in this article I am going to discuss what film grain actually is and then once that is understood, then we can apply grain to our images the proper way. When I say the proper way I mean let's apply this grain to our images in a manner that resembles how grain manifests itself in the film world.

This is the image that I going to use in this tutorial. And, more specifically, the sky portion with clouds.

I come from the film world and I can actually say that I have spent countless hours in the darkroom attempting to come up with some of the finest grain possible, especially when using high ISO (ASA for us old dogs) rated films. And for the purpose of this article and in my mind, I will be referencing black & white films ... although I believe the principals and concepts are the same for color films.

The reason I say that I will be referencing black & white films is because it is a lot easier for me to explain and for you to understand - think in terms of greyscale ...

What has been called grain in photographic film is now called digital noise. Having grain show up in your film and subsequently in your prints is all part of the photographic film process. Silver is embedded into the emulsion of films and is the light sensitive material used to record your images. There is a complete chemical process that goes on when developing your films and I am sure you may have heard the phrases Silver Crystals, Silver Halides & Silver Salts - this is some of the stuff that helps create your images. These silver crystals vary in size, orientation and distribution in the film's emulsion. These are the light sensitive particles in your film.

In Black & White photography, silver is used extensively in making various film types and photographic printing papers. There really is something beautiful about silver prints. And then things went downhill for quite a while when the price of silver started to raise back in the late 70's and early 80's. Manufacturers started using less silver, which gives you those deep rich blacks, and started using whiteners to compensate for the lack of contrast because of the reduced silver content. Adding whiteners to the printing papers helped give the appearance of a contrasty image but in my opinion, lacked the richness and depth of original silver based printing papers.

For finer grain, use a lower ISO rated film - for more coarser grain, use higher rated ISO films. Conversely, the higher the ISO, the more visible the film grain. Another contributing factor in grain size or appearance is the film developer used to process the film. That is a topic for another discussion.

As random as film grain is in its size, orientation and distribution and based on the nature of the chemical photographic process, it appears that the grain is less noticeable in the highlight areas and more noticeable in the mid-tones and shadows.

To sum things up at this point, it is the silver content in its various forms that creates the film grain we have come to know and some would say expect to see in photographic images.

What is Digital Noise?

In today's modern digital cameras we see the equivalent to film grain, known as digital noise, which is generated at the sensor level and for the most part is a byproduct of heat generated. What the heck does that mean, eh? The harder the photosites on a camera's sensor has to work to receive the information,  more heat is generated and shows up as random coloured speckles in the images.

Most people strive to get rid of as much digital noise as possible, which results in a very clean image. Some would say, "too clean" or "synthetic" or it looks "too digital". And this is where the discussion of adding grain back into our images stems from.

There are as many ways to add grain into our digital images as there are days in a month. The question is; which ones work the best, the quickest and the easiest? We all know that easy is quick but not necessarily the best.

I have seen a lot of articles on this topic, some not as good as others but none-the-less, people use them and their results may not be as good as they could have been.

Adding Grain to your Digital Photographs ...

For me, the best way to add realistic film grain to my digital images is to use Adobe Photoshop taking advantage of Layers, Layer Blend Modes, Layer Opacity, the Filter Gallery choosing the Grain Category or going under the Filter Menu and choosing Noise > Add Noise and starting out with the dialog's default settings with the exception of choosing the Monochrome option. If you decide to use the Filter Gallery to add noise, you will also have to desaturate your noise layer - the default from this category is coloured noise and we don't want skittles in our images, right?

Although you can add grain to your images in Lightroom, I prefer to use Photoshop because I have more options to get the grain just the way I want it. Hold this though because I want to come back to it later on in the article.

Photoshop Method 1: The Add Noise Filter Method

This method has been around for decades - way before the Filter Gallery ever existed. It is simple to use and gives amazing results. So, open the image that you want to add some grain to in Photoshop.

Step 1: Create the Grain Layer by going to the Layer Menu and choosing New Layer - in the resulting dialog give this Layer a unique name such as Grain-01.

Step 2: Change the Layer Blend Mode from Normal or SoftLight - notice that the check box below SoftLight is now selected indicating that the layer will be filled with 50% grey. That is what we want.

Step 3: Now that this is done let's go to the Filter Menu and choose Noise > Add Noise - we can start off with the default values and check the Monochrome check box.

Step 4:  So now you have this Grain Layer sitting on top of your image Layer and because we are using one of Photoshop's Contrast Blending Modes (Soft Light), anything lighter than 50% grey does not show up in that Layer, anything that is darker than 50% grey does. ( I do have a complete tutorial on Photoshop's Layer Blending Modes which I will post later on.)

Looking at your image right now you will see the grain being applied. If it is too much, just reduce the Grain Layer's Opacity down from 100% until you like what you see.

We are not finished but let's move onto Photoshop Method 2.

Photoshop Method 2: The Add Grain Method using the Filter Gallery

Step 1: With the image open that you want to add some grain to, create a new blank Layer as you did in the previous example naming this Layer Grain-02, change the Mode to Soft Light and selecting the check box for "Fill with Soft-Light-neutral color (50% grey)".

Step 2: Now go under the Filter Menu and choose Filter Gallery - ( again I have a complete tutorial on the Filter Gallery) and then click on the right pointing arrow for Texture.

Now if this is not strong enough, then just increase the Intensity to your desired taste. Just leave the Grain Type set to Regular for now - you can experiment later.

Now that is Intense for sure ... Notice the coloured grain. This is not what we want - we want our grain to be neutral so the easiest way to do that is to Desaturate the layer itself. Click OK to dismiss this dialog box.

Step 3: Now go under the Image Menu > Adjustments > Desaturate.

Step 4: Save these images with unique names so you can identify them at a later date if you want to revisit how this was done. Also, a good idea would be to name your new Layers based on what you have done possibly including the slider values to help you in the future.

Now comes the fun part. Take a look at your images with your newly added grain and compare. They should be basically the same except for the intensity of the grain itself. You can play with the sliders in both the Add Noise dialog box and or the Filter Gallery dialog box to get to what you think is good grain for your image(s).

Most people are satisfied with what they have at this point but I wouldn't be and neither should you after reading this article. So let's make it better. When I say better, I mean more realistic like film grain from the film days. After all, this is what we are trying to recreate isn't it?

Film grain in the film days is generated by the chemical process applied to the film. If you take notice of prints from film photography, you should notice that there is less to none film grain in the highlight areas and more noticeable in the darker regions of the print. So what we have to do is apply this film grain layer to our underlying image layer in such a way as to limit the grain in the highlight areas and allow it to pass through to the darker areas. Does this make sense? I hope so. We need to get this grain layer to feed into the image in an organic manner. We are going to do this by masking out certain areas.

Step 5: In Photoshop, turn the layer visibility off for any and all Layers except for the Background. Nested in with the Layer's Panel is also Channels and Paths. Click once on the Channels Tab to bring the Channels Panels to the front. You will notice that there are four channels; RGB, Red, Green & Blue. Right now we are only interested in this RGB composite channel. We want to load this channel as an active selection and apply it as a Layer Mask to the grain layer. To do this, simply hold down the Command Key on a Mac or the Control Key on Win and click your mouse. You should now see the active selection in your document window.

Step 6: Click back on your Layer Tab and turn on the visibility of your Grain Layer and click once on the Grain Layer to make it the active Layer.

Step 7: Now go to the bottom of the Layers Panel and click once on the "Add Layer Mask" icon to add a layer mask based on the active selection.

This is what your Layers Panel should be looking like. Here I am using method #1 but could have just as easily shown method #2 ...

To the right of your Grain layer - I named mine SoftLight Blend Layer - is the Layer Mask. This Layer Mask is basically a greyscale version of your colour image. The way Layer Masks work is; anywhere you have white, everything on that Layer shows through and where there is black, everything is hidden and all the shades of grey in-between allow varying amounts of the grain to show through based on how light or dark certain areas are. 

So in this case, the grain is showing through the opposite areas that I want it to show through - it is now showing through the clouds and other light areas and I want to block it off from showing through the clouds and light areas. In order to do this I need to Invert the Layer Mask.

Step 8: To Invert the Layer Mask, first you have to click the mask once to make that the active component on that layer. Then go under the Image Menu > Adjustments > Invert.

And as always, if the effect appears to be too strong, just reduce that Layer's Opacity. Something else to think about is the intended use of the image - is it for web display or being printed? The effect needs to be stronger if the image is being printed in order to compensate for ink drops going onto and into paper.

Below are examples of what the image looks like without a grain layer, with a grain layer, with a normal layer mask applied to the grain layer and finally with that layer mask inverted. These are also zoomed in to 200% for an exaggerated view for demonstrated purposes.

Hopefully you can see the differences in these images below.

This first image is the straight image with no grain added.

This second image has the grain layer added. As you can see, the grain is throughout the entire image.

This next image has the layer mask applied to the grain layer. As you can see, the intensity has been reduced but the grain is showing more in the lighter areas and we want the opposite so ...

In this last image, the layer mask has been inverted to stop the grain effect from showing through the lighter areas as in traditional film photography.

Hopefully you can see the differences in these images

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A great discussion in much more detail can be found here - just scroll down a bit to get to the way too technical conversations between Bob & Ron: 

https://www.photo.net/discuss/threads/which-causes-more-grain-under-or-overexposure.134963/

Adobe also has an article on this topic as well:

https://www.adobe.com/creativecloud/video/discover/film-grain.html