You can add these by clicking the Create Adjustment Layer icon in the Layers panel. Choose from options like Levels, Hue/Saturation and Photo Filters. Each adjustment will appear as a separate layer and affect all the layers underneath. This is useful in multi-layer documents and with composites as adding a tonal change helps the different elements to gel together. Making the effect on a separate layer brings several other benefits too. The adjustment remains endlessly editable (double- click the thumbnail to re- enter the settings) and we can adjust the opacity to change its strength, choose a different blend mode, or paint a layer mask to make the tonal effect work selectively over specific parts of the image.