A free tutorial on manipulating colour using the Curves adjustment layer for a cross-processing effect
Go to Layer>New Adjustment Layer>Curves to edit colour. Select the Red channel and create an ‘S’ shape by dragging the line of the graph. The amount of red variation is personal preference.
Select the Green channel from inside Curves and apply a similar ‘S’ shape. The more the curve is bowed the more contrast and colour is added to your image.
Select the Blue channel and apply a reverse ‘S’ shape to the graph than what was done with the Red and Green channels. This gives shadows a tint of blue that’s distinctive with cross processing, but there are no rules to this effect.
Add a Brightness/Contrast adjustment layer and increase the Contrast slider to 20. Set Brightness to 15 to strengthen the highlights. This gives your image the authenticity needed, with high-contrast tones and tinted shadows.