How to increase contrast in a photo
Upload an image and the Adjust tab opens with contrast at 125 percent, a moderate boost that suits most flat photos. The slider runs from 0 to 200 percent, with 100 as the original. Higher values push dark tones darker and light tones lighter, spreading them away from the image's average tone; lower values pull them together toward a flat grey.
Raising contrast makes edges and textures stand out and gives photos a crisper, more three-dimensional look. Lowering it creates a soft, faded or matte look, and can calm down a picture taken in harsh midday sun.
When a photo needs more contrast
Photos taken through a window, on a hazy or overcast day, or of a screen often look grey and lifeless. Scans of old prints and documents frequently look the same way. These are the cases where a contrast boost helps most. For scanned text, higher values make the letters darker and the paper whiter, which improves readability.
Watch the extremes. Above about 150 percent, shadows can block up into solid black and highlights can clip to white, and skin tones can look harsh or orange. If dark areas lose detail, lower contrast a little and raise brightness slightly to compensate.
Contrast, brightness and saturation together
Contrast also makes colours look more intense, so after a large boost you may want to bring saturation down a touch. If the photo is both dull and dark, raise brightness first and then add contrast. All three sliders are in the same Adjust tab, and you can switch to grayscale for a high-contrast black and white image. The server renders the result at full resolution; PNG stays PNG and other formats become JPG.