lllyasviel / lllyasviel/stable-diffusion-webui-forge

Putting a negative prompt will reduce the image quality

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Python
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Description

Hello guys,

Just want to point out something a friend of mine noticed and that i was able to verify on my side,
For some reason, adding a negative prompt will worsen the image quality a lot (atleast on SDXL models),
This is something that i was able to verify on "Pony Diffusion XL V6" and NoobAI (both EPS 1.1 and VPred 0.65).

You can check with this prompt:

Sampler: Euler A
positive:
1girl, portrait, white background, long hair, blonde hair, green eyes, tshirt, looking at viewer
negative (can be anything else doesn't matter):
jpeg artifacts

This issue seems to not be present on ComfyUI, and i didn't verify but my friend told me that it's the same on the original fork (A1111).

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Research direction

Start by reproducing the reported quality drop with the listed positive and negative prompts on Pony Diffusion XL V6 and NoobAI, using Euler A. Compare the result with ComfyUI and, if available, the original A1111 fork. Done means adding the negative prompt no longer causes the reported image-quality degradation under the same setup.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
machine-learning
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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