NVIDIA / NVIDIA/Model-Optimizer
Diffusers Example quantize.py: --calib-size help text is misleading (acts as number of samples/prompts, not “calibration steps”). Suggest clearer name/alias and ceil batching.
@jingyu-ml is already working on this.
Since Nov 17, 2025.
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Description
The CLI flag --calib-size is documented as:
“Number of calibration steps.”
But in the script it’s used as the number of calibration samples/prompts, then divided by --batch-size to compute how many batches to run once. This is easy to misinterpret as “steps/epochs.”
Concretely, the code does:
• args.calib_size = args.calib_size // args.batch_size
• do_calibrate(...) iterates over batches of prompts and breaks when i >= calib_size (so: one pass, limited to that many batches).
Result: --calib-size 128 --batch-size 2 runs 64 batches × 2 prompts = 128 images total, not “128 calibration steps.”
This confused me because “steps” usually implies repeated passes/epochs, not “samples.”
FWIW, the Model Optimizer docs describe PTQ calibration as running on a small set of samples (typically 128–512), which matches the implementation, so the help text should say “samples/prompts,” not “steps.” 
Proposed fix (backward-compatible)
Clarify the help text and add an alias that reflects the actual meaning:
$-$ parser.add_argument("--calib-size", type=int, default=128,
$-$ help="Number of calibration steps.")
$+$ parser.add_argument("--calib-size", "--calib-samples", dest="calib_size",
$+$ type=int, default=128,
$+$ help="Number of calibration samples (prompts/images). "
$+$ "Internally divided by --batch-size to compute how many batches to run once.")
Why this matters
• Prevents users from over- or under-estimating calibration runtime (especially at high resolutions/long --n-steps).
• Aligns the CLI with the docs’ guidance that PTQ uses a small number of samples (128–512), not multiple epochs. 
Thanks for considering! Happy to submit a PR with the above diff if that helps.
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