Add Smart Noise

How To:

Add noise to an image while protecting the highlights and shadows.

Although reducing noise and grain is a common image editing task, one may also wish to add masked, isolated noise to an area of an image after retouching, or to reduce banding in gradients or even globally to the entire image, simply for artistic reasons. An undesired result of the Add Noise filter is that it also introduces noise into the extreme highlights and shadows (although there are some tasks, such as retouching blown highlights where one may wish to introduce noise into pure white areas). Using the optional properties of layers, one can create a 'smart noise' layer that is superior to simply adding noise directly to the image data in normal blend mode.

1. To create a new noise layer, opt/alt click the new layer icon in the layers palette and select Overlay as the blend mode and select the Fill with Overlay Neutral Colour checkbox option (which will fill the layer with 50% gray values, which are treated as transparent in Overlay mode).

2. Run the Add Noise filter with the desired settings to add the appropriate amount of noise. 

3. One may wish to scale the noise layer to a larger size, to produce larger noise/grain. This is often required when attempting to match the appearance of existing grain found in the image or when working in high resolutions. One can additionally apply sharpening, blurring, desaturation, contrast boosting curves, embossing or other operations to the noise layer to refine the results. 

Tip:

After scaling a noise layer, the hidden scaled data that now exists outside the visible canvas will bloat the file size of the layered document. If one is not concerned with preserving any hidden data found in other layers, one can Select All and use the Crop command. If later compositing flexibility is required in the other image layers, it is best to crop a duped file and replace the large noise layer with the cropped one - so as to preserve the hidden "Big Data" found in the other image layers beyond the canvas edges.

Perhaps make a feature request at the appropriate Adobe user forum if you would like the crop command to have the option to only crop big data from targeted layers, rather than every layer.

RGB, CMYK & Overlay Mode Noise:

Due to the subtle, finer appearance of CMYK Overlay noise, I favour removing RGB noise layers from the file and remaking them once in CMYK mode. CMYK mode Overlay noise layers should have the K channel unchecked in the Layer Style Blending Options so that no K noise is added, additionally, Blend-If sliders or endpoint layer masks should be added to isolate the noise from the extreme shadows and highlights (unlike RGB mode, Overlay blend in CMYK mode may need this extra step to protect the endpoints).

This is not a requirement, one may keep their RGB mode noise layers, when converting an RGB image with an Overlay noise layer to CMYK mode, simply merge the layer down or flatten the image before or during conversion.

Using Overlay blend mode in the noise layer produces a lesser graduated noise effect towards the endpoints and protects pure black and white tones from noise. This often provides a more natural, pleasing transition of noise than when simply used in normal blend mode directly to the original image pixels. One can also further refine the addition of noise to specific tonal ranges using the Blend-If sliders found in the Layer Blending Options dialog box, or by using a "bell curve" layer mask.

For a minimal monochromatic affect, apply colour noise then immediately after the filtering process, use the Fade command to blend the noise in Luminosity blend mode. At the same filtering setting, Monochromatic noise is stronger than colour noise which has been luminance blended. Gaussian noise has a clustered noise pattern and produces a stronger result than Uniform noise at the same filter setting. Also of note, Uniform noise does not extend as far into the extreme tonal ranges as Gaussian noise.

When working in CMYK mode, one usually does not wish to introduce noise into the K channel. Simply uncheck the K channel checkbox found under Advanced Blending in the Layer Blending Options dialog so that only CMY noise from the noise layer is added to the final image. Layer masks or Blend-If sliders should also be used to protect the extreme shadow and highlights from noise.

Monochromatic Noise Evaluation (10 pixel @ 72 ppi)

Original Gradient
Uniform Noise
Uniform Smart Noise
Gaussian Noise
Gaussian Smart Noise 

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Related Links:

How To: Midtone/Endpoint Mask