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About this tool
Detect motion blur, lens blur, and out-of-focus regions in images with blur heatmap visualization and AI suggestions.
Blur Detector measures how sharp a photo is by converting it to Rec.601 luminance, averaging the brightness difference between each pixel and its right and lower neighbours, and turning that gradient energy into a sharpness score, a blur percentage and a six-step verdict from Sharp down to Severe Blur. It also tiles the image into blocks and paints a red heatmap over the softest ones, so you can see whether the whole frame is soft or only part of it. It is a quick triage pass for photographers and anyone culling a shoot, not a substitute for zooming in at 100 percent.
Open Blur Detector on AltFTool — it loads instantly in your browser.
Drop a photo onto the 'Drop image here or click to browse' panel, click it to pick a file, paste one from the clipboard, or press Camera and then Capture. JPG, PNG, WEBP and HEIC are accepted, up to 20MB.
Analysis runs on its own as soon as the image loads. The Blur Level, Sharpness and Focus gauges appear beside the preview, and Analysis Details lists Blur Type, Blur Percentage, Edge Density, Focus Area and Focus Confidence.
Press Blur Heatmap to shade the softest blocks of the frame in red and Original View to switch back, read the AI Suggestions panel for shooting fixes, and use New Image to clear the result and load another photo.
Reports sharpness, blur percentage, edge density and focus area as separate figures instead of a single vague pass or fail.
Splits the frame into blocks and shades each one by its own local gradient, so a sharp subject on a soft background scores differently from a uniformly soft frame.
Analysis runs on the image's native pixel data drawn to a canvas, not on a downscaled preview that would smooth away the detail being measured.
It computes the mean absolute luminance gradient across the image — for every pixel, the brightness difference to the pixel on its right plus the pixel below — and scales that against a reference of 30 to produce the sharpness score. Blur percentage is simply 100 minus that score, and a value above 50 triggers the shooting suggestions.
They are severity bands on the same average gradient value: under 5 is Severe Blur, under 15 Significant, under 30 Moderate, under 50 Slight, under 80 Minimal, and anything above that is labelled Sharp. They describe how much blur is present, not whether it came from camera shake or missed focus.
It is the share of pixels whose gradient magnitude exceeds 30, expressed as a percentage — effectively how much of the frame carries hard detail. A crisp architectural shot scores high, while a correctly focused portrait against a smooth backdrop can score low without being blurry, so read it alongside the heatmap rather than on its own.
Because the measurement is global: intentional background bokeh lowers the average gradient exactly the way a missed focus does. Switch to the heatmap view — if the red overlay covers the background but leaves your subject clear, the frame is doing what you intended.