Adjust Channel Levels

[sanmarcos]

I am trying to replicate a Photoshop effect. Image > Adjustments > Levels

Settings:
red: 0, 1.11, 230
green: 0, 1.14, 238
blue: 29, .81, 255
combined: 11, 1.29, 247

Input image:


Output image:



I tried doing something like

Code: Select all

MagickSepiaToneImage(magick_wand, 0.8 * QuantumRange);

But this isn't really a sepia effect, it is more of a 'washed' look

[el_supremo]

Have you tried this function?
http://studio.imagemagick.org/api/magic ... LevelImage

Pete

[fmw42]

In command line mode, try this (the conversion by quantum range is not needed if you are running Q8 IM otherwise you need to specify colors within the full quantumrange 0-65535 for Q16 or convert to 0-100 percent values):


r1=0
r2=`convert xc: -format "%[fx:quantumrange*230/255]" info:`
g1=0
g2=`convert xc: -format "%[fx:quantumrange*238/255]" info:`
b1=`convert xc: -format "%[fx:quantumrange*29/255]" info:`
b2=255
convert dWe0q.png \
-channel r -level $r1,$r2,1.11 +channel \
-channel g -level $g1,$g2,1.14 +channel \
-channel b -level $b1,$b2,0.81 +channel \
dWe0q_result.png


see -level at http://www.imagemagick.org/Usage/color_mods/#levels

Note I edited the values to correct some copying mistakes on the values.

[sanmarcos]

I used this, which gets a pretty close result to what I needed.

MagickLevelImageChannel(magick_wand, RedChannel, 0.0, 1.11, 230);
MagickLevelImageChannel(magick_wand, GreenChannel, 0.0, 1.14, 238);
MagickLevelImageChannel(magick_wand, BlueChannel, 29, 0.81, 255);

Targetted image:


ImageMagick produced image:


I must point out that Photoshop is doing this with its level corrections, not sure if ImageMagick has any counterparts to this:

[fmw42]

try adding -contrast-stretch 1% or 2% (or the equivalent -- adjust as needed) after the -level to account for the clipping included in PS

[el_supremo]

I tried this out with MagickWand and when I add a MagickLevelImage to do the "combined" parameters you gave, it seems to be pretty close to your target image.
Add this after the others:

Code: Select all

MagickLevelImage(magick_wand,11,1.29,247);

Pete

[sanmarcos]

I have made some adjustments, and it is so close that if it I did not have the images side by side, I could not tell the difference. One of them looks slightly darker/lighter, no big deal.

Thanks for your help!

Code: Select all

        MagickLevelImageChannel(magick_wand, RedChannel, 0.0, 1.11, 230);
        MagickLevelImageChannel(magick_wand, GreenChannel, 0.0, 1.14, 238);
        MagickLevelImageChannel(magick_wand, BlueChannel, 29, 0.81, 255);                
        MagickLevelImage(magick_wand, 11, 1.29, 247);
        MagickContrastStretchImage(magick_wand, 0.10, 0.10);