Enhance an image

What makes a photo look dull

Most disappointing photos are not badly composed; they are flat. Phone cameras play it safe in tricky light, so shots taken indoors, through haze, at dusk or into the sun come out with grey shadows, muted colour and soft edges. The information is all there in the file. It just needs its contrast stretched, its colour lifted and its edges defined. That is exactly what this enhancer does, and it does it on your device in a fraction of a second per photo.

The three corrections

• Auto levels. The enhancer looks at the darkest and lightest pixels in the photo and stretches the range so the darkest become true black and the lightest true white, clipping a tiny fraction at each end so a single bright highlight does not throw the result off. Each colour channel is treated separately, which also removes mild colour casts from indoor lighting.
• Colour lift. Saturation is raised by a modest amount, between 6 and 18 percent depending on the strength you choose. Enough to make food, skies and skin look alive again, not so much that it looks like a filter.
• Smart sharpening. An unsharp mask compares each pixel with its neighbours and boosts the difference, which makes edges crisper without adding noise to smooth areas. Strong applies two passes.

Choosing a strength

When to add the 2× upscale

Switch it on for small images that will be shown larger than they are: a 600 pixel product photo that needs to fill a 1,200 pixel slot, an old low-resolution photo for a slideshow, a thumbnail you want to print. The image is enlarged with high-quality resampling before sharpening, which keeps edges cleaner than enlarging afterwards. It cannot invent detail that was never captured, so a tiny, blurry photo becomes a larger, cleaner, still-soft photo; for graphics and logos the results are excellent.

What it will not fix

• Motion blur or missed focus. Sharpening defines edges that exist; it cannot create edges that were smeared.
• Heavy noise from very dark scenes. Sharpening makes noise more visible, so use Light on those.
• Blown-out highlights. Detail lost to pure white in the original cannot be recovered.
• Composition, straightening or retouching. Use the crop and rotate tools, or a full editor.

Batch use

Photos from the same event tend to share the same problem, so pick a strength on one and drop the whole set. Every image is corrected individually (the levels are measured per photo), then downloaded together as a ZIP. Nothing is uploaded at any point.