Grain added in Photoshop is normally the most obvious clue that an image was taken with a digital camera rather than on film. Film grain is created by the clumping of the silver halide crystals in the negative and is dependent on the type of film and the distribution of light and dark tones on the negative. Digital noise is even over the entire image and is normally too even to produce a realistic result, but there are a few trick you can use to improve the final image.
Create a new blank layer and fill with 50% grey. To do this click on the New Layer icon at the bottom of the Layers Pallet, then from the Edit menu select “Fill”. In the dialogue box that appears choose “50% Gray” from the drop down menu and click OK. Your image will disappear behind a grey layer.
Change the blending mode of the new layer to “Soft Light” by choosing “Soft Light” from the Blending Modes menu in the Layers Pallet. Your grey layer will now disappear and you will be able to see your image again. Another option is to use Overlay as the blending mode and this provides a slightly different effect. Experiment to see which you prefer later.
With your top layer still selected go to the Filters menu and select Noise>Add Noise. Make sure that Gaussian and Monochromatic are both selected and then choose the amount of noise to add.
The amount setting depends on your personal taste and you might have to try several settings to get your final, desired result. If in doubt it is better to add slightly too much grain as it is easier to reduce the effect later than add in more grain. For the sample image try a value of about 25%. Click OK.
From the Filter menu select Blur > Gaussian Blur and use a very small amount to blur the grain.
Try using a value of 1 to start but again this depends on personal choice and also the resolution of your image.
Digital grain is too regular in shape so we are going to distort the shape of the grain slightly. Press the letter F on the keyboard so that you get a grey area around the image. This is your working area and gives you a little more space to move for the next step. Press Control+T on your keyboard to transform the grain layer.
You will see “Grab Handles” appear in the corners of your image Click one of these handles and drag a little way to one side and further up or down. The idea here is that we are stretching the grain layer a different amount in each direction. For those of you with a mathematical mind try going about 5% in one direction and 35% in the other. Press return on the keyboard to accept the transformation. Press the letter F on your keyboard twice to get back to the default view.
You can now reduce the opacity of the grain layer if you feel the effect is too strong and it is a good idea to rename the layer to something like “Film Grain”. You can see the before and after effect in the cropped images below.