Colour Calibration
The instructions on this page will allow you to calibrate your monitor, digital camera and printer to use the sRGB colour space. This is no substitute for proper ICC profiles for your equipment, or a calibration device like the Colorvision Spyder, but should produce results good enough for most non-professional uses. We get better results than the manufacturer’s own ICC profiles using this method. Your mileage may vary.
The monitor will be calibrated “by eye”, and Argyll will be used to produce ICC profiles for the camera and printer to match the monitor. The result will be a simple colour-managed workflow, wherein photographs are displayed accurately by the monitor, and prints accurately reproduce what is displayed on the monitor. The workflow is closely tied to the monitor, so any changes to the monitor’s settings may cause problems.
Calibrating the monitor
Move the following image to the centre of the screen:
Adjust each control on the monitor until the two shades in the image are almost indistinguishable.
When adjusting the gamma, red, green and blue controls, it may help to move away from the monitor or squint slightly.
Calibration depends on the colour of the ambient light. Light the room the way it would normally be lit while you work.
If both your video card and your monitor offer these controls, adjust the video card first.
Calibrating the camera
These instructions require Argyll, The GIMP, Netpbm, and a monitor calibrated using the instructions above.
Create a test pattern:
targen -v -d3 -f4560 Camera
printtarg -v -s -iSS -p594x420 Camera
Display the resulting Postscript file Camera.ps on your calibrated monitor. Ensure the edges of the page are visible. Darken the room, and take a photograph of the screen, ensuring that the test pattern is as square as possible in the frame, and that the edges are included.
Load the photograph into The GIMP. Use the “Perspective” tool to adjust the image so that it contains only the pattern, including the corner marks and a small white border, and the horizontal and vertical lines are perfectly horizontal and vertical. Scale the image to 640x480 pixels, and save as Camera.jpg.
Convert the photograph to a 3-channel 24-bit TIFF file (I use pnmnorm here to stretch the contrast, so the resulting profile does not affect brightness too much):
jpegtopnm Camera.jpg | pnmnorm -keephues -bpercent 0 | pnmtotiff >Camera.tif
Scan the photo for colour information:
scanin -v Camera.tif Camera.cht Camera.ti2
Create an ICC profile:
profile -v -D"Canon S5 IS" Camera
(change the description field to a description of your own camera). The result will be an ICC profile Camera.icc.
You can test the profile by correcting the test pattern:
cctiff -e1 -ia Camera.icc Camera.tif corrected.tif
Compare the corrected image corrected.tif with the Postscript test pattern Camera.ps.
Calibrating the printer
These instructions require Argyll, The GIMP, Netpbm, the sRGB ICC profile sRGB.icm, and a camera calibrated using the instructions above.
Create a test pattern:
targen -v -d3 -f4560 Printer
printtarg -v -s -iSS -p594x420 Printer
Print the resulting Postscript file Printer.ps at high quality on your preferred paper, with all colour correction disabled (see your printer’s manual for how to do this). Darken the room, and take a photograph of the print using the flash, ensuring that the test pattern is as square as possible in the frame, and that the edges are included. Any glare will affect the results - move the flash or the camera to avoid this.
Load the photograph into The GIMP. Use the “Perspective” tool to adjust the image so that it contains only the pattern, including the corner marks and a small white border, and the horizontal and vertical lines are perfectly horizontal and vertical. Scale the image to 640x480 pixels, and save as Printer.jpg.
Convert the images to a 3-channel 24-bit TIFF file:
jpegtopnm Printer.jpg | pnmtotiff >Printer.tif
Scan the image for colour information, using the camera’s profile:
scanin -v -c Printer.tif Printer.cht Camera.icc Printer
Create an ICC profile:
profile -v -D"Canon iP4000 Kodak Picture Paper" -S sRGB.icm -cmt -dpp Printer
(change the description field to a description of your own printer and paper). The result will be an ICC profile Printer.icc - consult the manual for your software for how to use it. Always print with the printer’s own colour correction turned off, as this will severely affect the results.