magnus919_agent-skills/color-management/references/icc-profile-operations.md

ICC Profile Operations

Practical guide for common ICC profile operations using CLI tools.

ImageMagick

Convert image from one color space to another

# Convert from sRGB to ProPhotoRGB (relative colorimetric)
convert input.jpg -profile sRGB.icm -profile ProPhotoRGB.icc output.tif

# Specify rendering intent: 0=Perceptual, 1=Relative, 2=Saturation, 3=Absolute
convert input.jpg -intent Relative -profile sRGB.icm -profile ProPhotoRGB.icc output.tif

# With black point compensation
convert input.jpg -black-point-compensation -profile sRGB.icm -profile ProPhotoRGB.icc output.tif

Assign vs Convert

# ASSIGN (reinterpret existing RGB numbers with new profile — colors change)
convert input.jpg -profile sRGB.icm input-assigned.jpg   # if untagged
convert input.jpg -set profile 'sRGB.icm' input-assigned.jpg  # force assign over existing

# CONVERT (preserve colors, change RGB numbers)
convert input.jpg -profile sRGB.icm -profile ProPhotoRGB.icc output.tif

Extract embedded ICC profile

convert input.jpg profile.icc
identify -verbose input.jpg | grep -A 100 "Profile-icc"

Strip ICC profile

convert input.jpg +profile icc output.jpg

Get image color space info

identify -verbose input.jpg | grep -E "Type:|Colorspace:|Profile-icc"

Create difference image for comparing before/after

composite -compose difference before.tif after.tif difference.tif
convert difference.tif -fill white +opaque "rgb(0,0,0)" histogram.png

Count pixels altered by a conversion

composite -compose difference original.tif converted.tif diff.tif
convert diff.tif -fill white +opaque "rgb(0,0,0)" -format %c histogram:info:
# Black pixels = unchanged; White pixels = altered

ArgyllCMS

Check if a profile is well-behaved

# Interactive mode — type "255 255 255" then "0 0 0" then "128 128 128"
xicclu -ir -pl -s255 -v0 profile.icc

# Non-interactive: echo values to stdin
echo "255 255 255" | xicclu -ir -pl -s255 -v0 sRGB.icm
# Expected: 100.000000 0.000000 0.000000 for well-behaved at white

echo "0 0 0" | xicclu -ir -pl -s255 -v0 sRGB.icm
# Expected: 0.000000 0.000000 0.000000

echo "128 128 128" | xicclu -ir -pl -s255 -v0 sRGB.icm
# Expected: L* around 53-54, a*=b*=0.000000

Create a VRML gamut visualization

iccgamut -ir profile.icc profile.gam
viewgam -w profile.gam profile.wrl
# Open profile.wrl in a VRML viewer (view3dscene, etc.)

Convert between color spaces

# Using cctiff (Argyll CMS color conversion TIFF tool)
cctiff -i source_profile.icc -o dest_profile.icc input.tif output.tif

# Specify intent: -t 0=Perceptual, 1=Relative colorimetric, 2=Saturation, 3=Absolute
cctiff -t 1 -i sRGB.icm -o ProPhotoRGB.icc input.tif output.tif

Extract embedded ICC profile

extracticc input.jpg extracted_profile.icc

Profile a monitor (requires hardware colorimeter)

# See full ArgyllCMS documentation at https://argyllcms.com/
# Typical workflow:
# 1. dispcal -v -d 1 -t 6500 -g 2.2 -f 2.0 calibration_target
# 2. dispread -v -d 1 calibration_target
# 3. colprof -v -qh -D "My Monitor Profile" calibration_target

Profile a camera (requires IT8 target)

# 1. Photograph an IT8 target
# 2. Extract target values from the image
# 3. Run:
scanin -v targ_file.it8 target_measurements.ti3
colprof -v -qh camera_profile.icc target_measurements.ti3

Exiftool

Show all ICC profile metadata

exiftool -ICC_Profile:all -G image.jpg

Show color space metadata (DCF tags)

exiftool -ColorSpace -InteropIndex -WhitePoint -PrimaryChromaticities -Gamma image.jpg

Show all metadata (quick overview)

exiftool -a -S -G0 -ColorSpace -InteropIndex -ICC_Profile:all image.jpg

Remove embedded ICC profile

exiftool -ICC_Profile= image.jpg
# Makes backup: image.jpg_original

Embed an ICC profile

exiftool -ICC_Profile<=profile.icc image.jpg

LittleCMS (LCMS2)

Convert image using tificc

# Bounded mode (standard):
tificc -c 0 -w 16 -e -t 1 -i source.icc -o dest.icc input.tif output.tif

# Unbounded mode (32-bit floating point, requires true gamma TRC profiles):
tificc -c 0 -w 32 -e -t 1 -i source-g100.icc -o dest-g100.icc input.tif output.tif

tificc parameters:

• -c 0: 0=use LCMS, 1=use built-in sRGB
• -w 16|32: bit depth (16 or 32)
• -e: embed source profile in output
• -t 0|1|2|3: intent (Perceptual, Relative, Saturation, Absolute)
• -i profile.icc: source profile
• -o profile.icc: destination profile

Interactive lookup with transicc

# Start interactive session:
transicc -w

# Or pipe values:
echo "128 128 128" | transicc -w

Check profile type and capabilities

# transicc can reveal whether a profile uses matrix or LUT tables
transicc -v profile.icc 2>&1 | head -20

Firefox Color Management

about:config settings for Linux/Firefox:

gfx.color_management.enabled = true
gfx.color_management.mode = 1         (0=off, 1=full, 2=tagged only)
gfx.color_management.display_profile = /path/to/your/monitor/profile.icc

Firefox limitations:

• Does NOT support black point compensation as of 2015 (and likely since)
• Dropped LittleCMS after a security alert — rolled their own CMS
• V4 profiles may not work; use V2 for web export
• Shadow details will appear more crushed than in color-managed editors

GIMP 2.9+/2.10 Color Management

Key settings:

• Display rendering intent: Relative colorimetric with BPC (default)
• Only edit sRGB images — GIMP has hard-coded sRGB parameters
• LCH blend modes are a game-changer: separate Lightness, Chroma, Hue groups
• For radiometrically correct editing: use "Linear light" precision
• For safe out-of-gamut avoidance: use integer precision (clips automatically)

LCH Layer Setup (from Elle Stone's tutorial):

1. Duplicate scene-referred layer
2. Create three layer groups: Lightness (LCh Lightness mode), Chroma (LCh Chroma mode), Hue (LCh Hue mode)
3. Put layer copies in each group
4. Edit Chroma with Channel Mixer + Chroma mask from LCH decompose
5. Edit Lightness with Exposure, Curves, High Pass (desaturate each layer to Luminance first)
6. Edit Hue with Hue-Chroma tool
7. Outside of gamut colors: monitor with Color Picker + Sample Points
8. Before export: soft proof or clip to gamut