fix: correct Z-Image guidance scale threshold from > 1 to > 0#13094
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Mr-Neutr0n wants to merge 1 commit intohuggingface:mainfrom
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fix: correct Z-Image guidance scale threshold from > 1 to > 0#13094Mr-Neutr0n wants to merge 1 commit intohuggingface:mainfrom
Mr-Neutr0n wants to merge 1 commit intohuggingface:mainfrom
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Z-Image uses a non-standard CFG formula: pred = pos + scale * (pos - neg) Unlike the standard formula: pred = neg + scale * (pos - neg) With Z-Image's formula, any guidance_scale > 0 applies CFG effect. The previous > 1 check was incorrect and caused CFG to be ignored when 0 < guidance_scale < 1. Also updated docstring to document the correct Z-Image CFG formula. Fixes huggingface#12905
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Summary
Fix incorrect
do_classifier_free_guidancethreshold check in Z-Image pipeline.Problem
Z-Image uses a non-standard CFG formula:
Unlike the standard formula:
With Z-Image's formula:
guidance_scale = 0:pred = pos(conditional, no CFG)guidance_scale = 0.5:pred = 1.5*pos - 0.5*neg(partial CFG)guidance_scale = 1:pred = 2*pos - neg(standard CFG)Any
guidance_scale > 0applies a CFG effect. The previous> 1check was incorrect and caused CFG to be completely ignored when0 < guidance_scale < 1.Changes
do_classifier_free_guidanceproperty from> 1to> 0Fixes #12905