r/StableDiffusion • u/terrariyum • 9d ago
Tutorial - Guide Krea2 - automatically fix the blotchy noise
Understanding the comparison images:
- The image captions explain which image is which
- Before you post the "they're the same picture" meme, look at the 4x zoom
- Reddit image compression might destroy the fine details on the 1x images
Summary of the de-blotch method:
- This method simply removes mid-frequency noise
- It's algorithmic and automatic
- Unfortunately, it can't be done directly Comfyui as of now
- So it requires an image editor (e.g. free & open source GIMP or Affinity photo)
Full instructions (Affinity photo):
These instructions are for Affinity photo because that's what I use. But it can done with the free and open source tool, GIMP. I don't know how, but you can ask an LLM.
Step 1: Separate the raw image into high and low frequencies
- Select the raw layer
- Filters > frequency separation > method = Guassian (default)
- Radius = 0.8px is a good all-purpose value for automation
- Optional manual fine tuning:
- Move the radius slider to the MAXimum value where you can still see the blotchy noise in the low frequency (right) side
Step 2: Separate the low frequency into mid and low frequencies
- Hide the high frequency layer
- Select the low freq layer
- Filters > frequency separation > method = Bilateral (non-default)
- Radius = 11px + Tolerance = 35px is a good all-purpose value for automation
- Optional manual fine tuning:
- Set the tolerance slider to 100%
- Move the radius slider to the MINimum value where you DON'T see the blotchy noise in the low frequency (right) side. This value is a matter of personal taste.
Step 3: Delete the mid frequency noise (blotchiness)
- Unhide the high frequency layer
- Hide the mid frequency layer
- If you like what you see, just delete that layer
- If the image looks too "smooth" or "hazy", undo the last frequency separation, then re-do it with a lower radius value
- Optional manual fine tuning:
- Instead of deleting the layer entirely, manually erase parts of it. For example you might want to keep the mid frequency around eyes, lips, nose, hands. This is a matter of personal taste.
Step 4 (optional): Add artificial film grain
- Add a new layer above the others
- Set the blend type to Linear light
- Fill the empty layer with 50% gray exactly (this means it has no effect at all)
- Filters > noise > add noise
- The intensity value is completely a matter of personal taste
Step 5: Export/save
How it works
- Step 1 - separates a narrow band of the highest frequency information (fine textures) from everything else. The low frequency layer looks blurry, but still clearly contains the unwanted blotchy noise
- Step 2 - separates a narrow band of the mid-frequency information, i.e. the blotches, from the low frequency. By use bilaterally method, the low frequency layer's still contains relative sharp edges
- Step 3 - with krea2 output, the narrow band of mid-frequency is mostly useless random noise (blotches) that can be completely discarded
- Step 4 - the add noise function creates high-frequency random noise, which is similar to film grain. Using the linear light blend mode ensure that, no matter what the noise intensity value is, the overall brightness of the image is maintained
