Color Adjustments & Effects
Brightening an image, boosting contrast, adding a glow to make it look cool... these are everyday steps for designers and illustrators.
In image generation, these features are sometimes used as "preprocessing" to get images into a shape that's easier for AI to work with.
There are plenty of image-processing custom nodes, and they can do much more advanced things, but honestly, a lot of the time it's just easier to use the paint tool you already know.
You don't have to do everything in ComfyUI.
Basic Processing
Invert Image Node
Generates a negative image with inverted RGB values.
Image Sharpen Node
Sharpens the outlines.
Image Blur Node
Blurs the image.
Image Quantize Node
Reduces the number of colors (posterization).
ImageAddNoise Node
Adds noise to the image.
It's a bit niche, but there's a technique where you deliberately add noise before image2image to get more detail even at a low denoise setting.
cf. Adding noise to pixel images to increase details in image2image with low denoise
Morphological Transformation
It may not be a term you hear often, but it's mainly used on black-and-white mask images. It lets you do things like "thicken lines (dilation)" or "remove noise (erosion)."
cf. OpenCV-Python/Morphological Transformations
Full-scale Color Correction (Custom Nodes)
There are countless custom nodes that add more practical, Photoshop-style image editing features. Here's one that covers the basics while staying simple and easy to use.
ComfyUI-Image-Effects
It includes most of the adjustments a person would want to make, such as hue/saturation/value (HSV) adjustment, tone-curve-style adjustment, and various filters. See the repository's documentation for the full list of features.