The image histogram shows how the light and dark values of a photo are distributed: the horizontal axis is luminance from 0–255 and the vertical axis is the pixel count, with the red, green and blue channels and a luminance curve computed with Rec.601 overlaid, each of which can be toggled on its own. On the right it reports the mean, median and standard deviation of luminance, together with the share of pixels at luminance ≤5 (crushed black) and ≥250 (blown white); the “exposure diagnosis” turns those numbers into plain-language statements about being dark, bright or normal, how much is clipped and whether contrast is high or low. The analysis runs locally in the browser.

It only diagnoses and does not modify: to act on the diagnosis, use the curves in the workbench's “Image Adjust”, or hand the image to “Auto Enhance”.

1. 01Upload one imagesingle mode; a very large image is first scaled to a longest side of 2048 before the statistics are computed, which barely affects the shape of the distribution.
2. 02Read the histogrambelow it are marked 0 shadows, 128 midtones and 255 highlights; the four toggles “Red R”, “Green G”, “Blue B” and “Luminance” let you look at just the channels you want.
3. 03Read the statisticsfour figures under “Luminance statistics” — mean, median, standard deviation and the percentage clipped at the black and white ends.
4. 04Read the diagnosis“Exposure diagnosis” gives one conclusion per line, green for normal, blue for a note and yellow for a warning; for a night scene, a silhouette or a snow scene, judge it together with the intent of the shot.

Supported input

JPG / PNG / WebP / GIF / BMP / AVIF / HEIC, one at a time.

Sampling

an image with a longest side above 2048 px is scaled down before the statistics; fully transparent pixels are not counted.

Thresholds

dark below 100, clearly dark below 70, bright above 160, clearly bright above 190; clipping is a note at 1% and a warning at 5%; a standard deviation under 35 reads as flat and above 80 as very contrasty — all of these are rules of thumb.

Colour space

statistics come from the sRGB pixels after browser decoding; no RAW data and no pre-ICC-conversion values are read.

What it does not do

it does not modify the image, does not apply automatic levels or curves (use “Image Adjust” or “Auto Enhance”), and does not report the camera exposure parameters (use “EXIF Viewer and Remover”).

The pixel statistics are computed locally in the browser and the photo is never uploaded to any server; it is released when the page is closed.