This tool reads a photo's brightness histogram to flag blown highlights and blocked shadows, entirely in your browser — nothing is uploaded anywhere.
Processed entirely in your browser — your photo is never uploaded anywhere.
Builds a brightness histogram from the photo (256 levels, black to white) and reads it for common exposure problems: how much of the image is near-pure-black (shadow clipping), how much is near-pure-white (highlight clipping), and where the average brightness sits.
The bar chart is the histogram — the horizontal axis runs black (left) to white (right), and bar height shows how many pixels sit at that brightness. A tall spike hard against the left or right edge usually means clipping (detail permanently lost in that area, not recoverable by editing). Clipping above 5% at either end is flagged in the verdict: "Highlights clipping" or "Shadows blocking up", or "Overexposed" / "Underexposed" when the mean brightness is also high (over 185) or low (under 70). Clipping above 5% at both ends reads "High contrast".
A histogram is a bar chart of every pixel in a photo sorted by brightness, from pure black on the left to pure white on the right, with bar height showing how many pixels sit at that level. This tool builds one from your photo across 256 brightness levels and reads it for two specific problems: how much of the image is clipped to near-pure-black (shadow clipping) and how much is clipped to near-pure-white (highlight clipping).
A camera's rear LCD or a phone screen can lie about exposure, especially outdoors in bright sunlight where the screen itself is hard to read accurately. Checking the actual histogram — in-camera while shooting, or here afterward — catches blown highlights or crushed shadows a screen glance would miss. That's detail that's genuinely unrecoverable once clipped, unlike a shot that merely looks dark or bright on screen but still holds real information in the file.
Backlit subject against a bright sky
Sky fills a large part of the frame, subject in shadow
Tall spike against the right edge — highlight clipping over 5%, verdict "Highlights clipping", "Overexposed" if the frame is bright overall, or "High contrast" if the shadows clip too
Dim indoor shot without flash
Low ambient light, no fill light
Histogram bunched toward the left, shadow clipping over 5%, verdict "Underexposed" (or "Shadows blocking up" if the mean is not dark)
Balanced daylight scene
Even lighting, no extreme highlights or shadows
Histogram spread across the middle, minimal clipping either side, verdict "Well exposed"
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