Summary and lessons
Through this exercise and by consulting existing manuals, I found that colour cast can be corrected by using:
- Levels, for example by adjusting Input and Output sliders of individual colour channels
- Curves (also exist in Levels), by using a mid-tone (grey) eyedropper to set mid-tone range
- Hue/ Saturation, by applying adjustments to individual colours or to the image general colour scheme
- Threshold mode (Alt key) could be used to close in highlight and shadow points. These adjustments could be done in individual channels for accuracy.
- Some images work better in black and white so switching to black and white or single tone image is another option!
A useful technique is to establish at least one (ideally multiple) point of reference searching for neutral grey or mid tone colour. This reference colour point can then be used for comparison. A white reference point and a black reference point are also useful in colour correction process.
Although shot for the previous exercise, the images below demonstrate really well how colour cast can be identified by using a white reference point (stripes on the flag in this instance).
I found the Variations interface to be a useful guide and a learning tool to study the effect of Gamma adjustments and colour adjustment theory.
