Can GIMP import a 256-value lookup table into Colors > Curves?
Asked 5/30/2011
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2 answers
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I have a Technicolor CineStyle S-curve lookup table as a plain text file with 256 output values (0–255), one per line. GIMP’s saved Curves files use a different text format with sections like (channel value) and (samples 256 ...). Is there a way to use this 256-entry lookup table in GIMP’s Curves tool, either directly or by converting it to GIMP’s curve file format?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
3
Here is what I did:
Given the input file with one number per line:
0 ... 17 18 18 19 20 21 22 ... 244 244 245 246 246 247 247 248 ... 255
I copied it into Spreadsheet, divided each number by 255, and formatted all the values to 6 decimal places.
After that, I edited a saved Gimp curve, removed the Red, Green, Blue and Alpha channels and the points used to define the curve, replaced the 256 values with the new ones from Spreadsheet.
This is what it looks like:
# GIMP curves tool settings
(time 0) (channel value) (curve (curve-type smooth) (n-samples 256) (samples 256 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.003922 0.003922 0.003922 0.003922 0.003922 0.007843 0.007843 0.007843 0.011765 0.011765 0.011765 0.015686 0.015686 0.019608 0.019608 0.019608 0.023529 0.023529 0.027451 0.031373 0.031373 0.035294 0.035294 0.039216 0.039216 0.043137 0.047059 0.047059 0.050980 0.054902 0.058824 0.058824 0.062745 0.066667 0.070588 0.070588 0.074510 0.078431 0.082353 0.086275 0.090196 0.094118 0.098039 0.101961 0.101961 0.105882 0.109804 0.113725 0.117647 0.125490 0.129412 0.133333 0.137255 0.141176 0.145098 0.149020 0.152941 0.156863 0.160784 0.168627 0.172549 0.176471 0.180392 0.184314 0.192157 0.196078 0.200000 0.203922 0.211765 0.215686 0.219608 0.227451 0.231373 0.235294 0.243137 0.247059 0.250980 0.258824 0.262745 0.266667 0.274510 0.278431 0.286275 0.290196 0.294118 0.301961 0.305882 0.313725 0.317647 0.325490 0.329412 0.337255 0.341176 0.349020 0.352941 0.360784 0.364706 0.372549 0.376471 0.384314 0.388235 0.396078 0.400000 0.407843 0.411765 0.419608 0.427451 0.431373 0.439216 0.443137 0.450980 0.454902 0.462745 0.466667 0.474510 0.482353 0.486275 0.494118 0.498039 0.505882 0.509804 0.517647 0.525490 0.529412 0.537255 0.541176 0.549020 0.552941 0.560784 0.568627 0.572549 0.580392 0.584314 0.592157 0.596078 0.603922 0.607843 0.615686 0.619608 0.627451 0.631373 0.639216 0.643137 0.650980 0.654902 0.662745 0.666667 0.674510 0.678431 0.686275 0.690196 0.698039 0.701961 0.709804 0.713725 0.717647 0.725490 0.729412 0.737255 0.741176 0.745098 0.752941 0.756863 0.760784 0.768627 0.772549 0.776471 0.784314 0.788235 0.792157 0.800000 0.803922 0.807843 0.811765 0.819608 0.823529 0.827451 0.831373 0.835294 0.839216 0.847059 0.850980 0.854902 0.858824 0.862745 0.866667 0.870588 0.874510 0.878431 0.882353 0.886275 0.890196 0.894118 0.898039 0.901961 0.905882 0.909804 0.913725 0.917647 0.921569 0.921569 0.925490 0.929412 0.933333 0.937255 0.937255 0.941176 0.945098 0.949020 0.949020 0.952941 0.956863 0.956863 0.960784 0.964706 0.964706 0.968627 0.968627 0.972549 0.972549 0.976471 0.976471 0.980392 0.980392 0.984314 0.984314 0.988235 0.988235 0.988235 0.992157 0.992157 0.992157 0.992157 0.996078 0.996078 0.996078 0.996078 1.000000 1.000000 1.000000 1.000000 1.000000 1.000000 1.000000 1.000000 1.000000 1.000000)) # end of curves tool settings
When imported into Gimp, this is how the curve looks like:
Originally by user3922. Source · Licensed CC BY-SA 4.0
user3922
15y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—GIMP can use it, but not by importing the plain 256-line text file directly into Curves.
A practical workaround is to save a curve preset from GIMP, then edit that file manually. For a single luminance curve, keep the (channel value) section and replace its samples 256 ... values with your lookup-table values converted from 0–255 into 0.000000–1.000000 by dividing each number by 255. Format them as decimal values (for example, 18 becomes 0.070588).
You can remove the Red, Green, Blue, and Alpha sections if you only want the overall value curve, and you don’t need the point definitions if you’re using the full 256 samples.
So the answer is essentially: no direct import of that simple LUT text format, but yes, you can convert it by editing a saved GIMP curve file. The GIMP curve file syntax is a Scheme-like text format, so it’s possible to script the conversion if needed.
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