Blacks
Blacks set the very darkest point of your photo, the true black. The blacks slider controls how deep your darkest tones go. A little real black gives a photo backbone and keeps it from looking grey and washed out.
Hold Alt (or Option) while sliding to see, in white, where your shadows clip shut. A touch down gives a rich, powerful image. For a matte, filmic look, lift the blacks slightly instead: this is called 'lifted blacks' and gives that soft vintage feel you see in many film presets. Together with whites, this sets your complete contrast range.
Related terms
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.