Restoring quantum range after -evaluate min max

[geoland]

A short query.

Having applied -evaluate min=% and -evaluate max=%

where % = a chosen value

Is quantum range restored to the image automatically with the new values applied or is it necessary to normalize or auto-level the image.

I may be missing a salient point about IM operation.

[fmw42]

I do not think the image will be automatically stretched to full dynamic range by using -evaluate min or max. It just sets the upper/lower bound.

[geoland]

-auto-level might be necessary then.

[fmw42]

Code: Select all

convert -size 256x256 gradient: -evaluate min 50% result.png

Shows that the maximum value will be 50% gray and minimum value is 0. So it just clips at that value and does not stretch again to full dynamic range.

If you want it stretched, use -level or -contrast-stretch or add -auto-level after -evaluate

[geoland]

Thanks Fred. That's what I thought. Saved me a lot of playing around.

[snibgo]

Is quantum range restored to the image automatically with the new values applied or is it necessary to normalize or auto-level the image.

IM operations don't auto-level. If you want this, you need to explicitly ask for it.