-level black_point{,white_point}{%}{,gamma}

[ssbroad]

ImageMagick version

7.1.1

Operating system, version and so on

windows10

Description

I want to use ImageMagick to adjust the contrast of a manga image.

However, I found that using the parameter "-level 63,248,1.0", did not handle the image correctly.
I got a pure white picture.

When it was changed to "-level 24%,97%,1.0", it was handled correctly.

"Given one, two or three values delimited with commas: black-point, white-point, gamma (for example: 10,250,1.0 or 2%,98%,0.5)."

The document is allowed without the ‘%’, but actually gets the wrong picture.

Why?

[snibgo]

The documentation at https://imagemagick.org/script/command-line-options.php#level says:

Given one, two or three values delimited with commas: black-point, white-point, gamma (for example: 10,250,1.0 or 2%,98%,0.5). The black and white points range from 0 to QuantumRange, or from 0 to 100%; ...

So if you don't use percent %, the numbers are in the range from 0 to QuantumRange. If your IM is Q8, QuantumRange is 255. For Q16, it is 65535. For Q32, it is 4294967295.

magick -version will show your Q-number. To see you QuantumRange, you can:

magick xc: -precision 15 -format %[fx:QuantumRange] info: