How do you add noise to an image in Photoshop?

To add noise to an image in Photoshop, the first option is the appropriate method. By navigating to Filter > Noise > Add Noise, you access a dedicated tool specifically designed for this purpose. This filter allows you to introduce a uniform or Gaussian distribution of noise to your image, providing control over the intensity, distribution, and monochromatic or colored noise settings.

This method is straightforward and gives direct control over how much noise is added, which is essential for achieving specific artistic effects or simulating a particular type of grain present in film. It's a quick and efficient way to manipulate the texture and mood of an image.

The other options do not effectively add noise. The Noise Reduction feature, for example, is primarily used to minimize existing noise rather than introduce it. Adjusting opacity of a noise layer could alter the visual effect, but this method is less direct and would require creating a noise layer first, making it more complex. Similarly, applying a grain filter effect does add texture, but it is not the same as adding noise in the specific sense that the Add Noise filter provides, which allows fine-tuning of the noise characteristics.