Use Curves for colour correction
Curves are a powerful tool for contrast correction, due to their flexibility and the directly interactive nature of the dialogue in Photoshop and similar software
Curves are a powerful tool for contrast correction, due to their flexibility and the directly interactive nature of the dialogue in Photoshop and similar software. By manipulating the curve, it is possible to deftly balance exposure and take precise control over the density of highlights and shadows in your images. There is however another use for the feature that is not as often discussed these days – the correction of colour.
By using the eyedropper tools inside the Curves dialogue, you can quickly and easily remove unwanted colour casts and colour shifts, just as you might do using a White Balance tool in Camera Raw or Lightroom. You can also be more confident that the colour balance this creates is accurate than if you were to manually tweak the sliders in the Colour Balance dialogue.
It is best to work on an adjustment layer rather than the background layer, so go Layer > New Adjustment Layer > Curves or pick Curves from the adjustment window on the right hand side of the Photoshop workspace.
Start with the shadows
In the curves dialogue, click on the first eyedropper to target the shadows. The idea is not to edit the curve directly so leave this in its default position. With the shadows eyedropper, click on your image in an area of deep shadow to neutralise any colour cast in the lower end of the tonal range. Be sure to target the darkest areas, otherwise the tool may incorrectly register colour and exposure, resulting in unintended colour and brightness shifts.
Correct the full tonal range
Using the other eyedroppers in sequence, correct colour in the midtones and highlight areas of your shot. For highlights, click in the brightest area of your image to create the proper colour correction effect, as with the shadows. For midtones, click in an area of neutral grey, such as the tops of the towers in this image – denoted by the green circle. As the name suggests, midtones are halfway between highlights and shadows in the tonal range. You may need to try several areas until you find a perfect neutral grey to target. Just keep an eye on your image until you see a good balance of colour. If there is an obvious colour shift, try another target point.
Select your sampling sensitivity
A quick tip is to change your Sample Size for your eyedroppers to 3 by 3 Average rather than the default Point Sample option. This will tell the tool to look further away from your sample point for colour reference, making it less sensitive to inaccurate sampling point choice.