Removing Colour Cast with LAB Colour Mode

LAB Colour mode is a great way to fix a color cast and/or to adjust the luminance in an image.

Follow this step by step guide to try it out.

1. Open your image in Photoshop.

2. Duplicate the image by clicking the Image menu - Duplicate

3. Convert the image to LAB Colour by clicking the Image menu - Mode - LAB Colour

4. If your layers panel is not displayed press F7 to display it.

5. Add a new adjustment layer by clicking the Layers menu - New Adjustment Layer - Levels.

6 . You will see 3 options in the levels dialog - Lightness, a, b

Just a quick Note, I find it helps to start with an end goal in mind before playing with the colours.

• Lightness - This option does not control the colour but is used to change alter the luminosity in an image. Dragging the slider on the far left (your left) in makes the blacks lighter. Dragging the slider on far right (your right) in makes the whites lighter. Dragging the central slider to the left makes the midpoint darker and to the right makes the midpoint brighter.
• a (Red - Green) - This option adjusts the Red - Green channels within an image and operates on the same principle as the Lightness Slider above.
• b (Blue - Yellow) - This option adjusts the Blue - Yellow channels within an image and operates on the same principle as the Lightness Slider above.

7. Once happy with the colour and luminosity changes flatten the image by clicking the Layer menu - Flatten Image.

8. Change the image back to RGB Colour by clicking the Image menu - Mode - RGB Colour

9. At the point I select the whole image, copy it and paste as a new layer in my original as I may reduce the opacity of the LAB adjustment.