Check a Photo for Red-Eye
Upload a flash photo — every red pupil is listed with its centre, radius and confidence, so you know exactly what to retouch. Nothing is uploaded; the check runs in your browser.
About this tool
Red-eye is what happens when a flash fires straight down the lens axis: the light bounces off the blood-rich retina and comes back as a glowing red pupil. This tool finds those pupils and tells you exactly where they are — it is a checker, not a retoucher, so your photo is never modified.
Every red-dominant, saturated, bright pixel is grouped into a connected region; regions that are the wrong size or the wrong shape for a pupil (a red jumper, a brake light, a stripe of lipstick) are dropped. What survives is scored 0–1 on how red, how round and how square it is, and listed highest confidence first.
The whole check runs in WebAssembly inside your browser. The photo never leaves your device, there is no upload and no account.
A worked example
Upload a 640×480 flash portrait with two red pupils at roughly (210, 180) and (330, 182), leave every control at its default, and the report looks like this:
{
"width": 640,
"height": 480,
"candidate_count": 2,
"sensitivity": "medium",
"regions": [
{
"center_x": 210,
"center_y": 180,
"radius_px": 6.51,
"area_px": 133,
"average_red": 223.4,
"confidence": 0.812
},
{
"center_x": 330,
"center_y": 182,
"radius_px": 6.18,
"area_px": 120,
"average_red": 214.9,
"confidence": 0.774
}
],
"warnings": []
}
center_x/center_y are pixels from the top-left corner, radius_px is the
radius of the disc with the same area as the red blob, and average_red is the
mean red channel (0–255) inside it. Paste those coordinates into any editor's
red-eye brush and you are done.
Reading the controls
- Sensitivity —
lowonly accepts bright, strongly saturated red;medium(the default) catches typical phone and compact-camera red-eye;highalso flags dim, partly-corrected or orange "amber eye", at the cost of more false positives. - Smallest / largest radius — the pupil size window, in pixels. On a big photo raise the minimum to skip JPEG noise; lower the maximum to reject large red objects.
- Maximum regions listed — caps the
regionsarray.candidate_countalways reports how many were found before the cap, and a warning tells you when the list was clipped.
Limits worth knowing
- PNG and JPEG only, up to roughly 48 MB of decoded pixels — re-export a huge photo at a lower resolution if you hit that.
min_radiusaccepts 1–80 px,max_radius1–300 px,max_regions1–100, andmin_radiusmay not exceedmax_radius.- Fully transparent pixels are ignored, so a cut-out PNG will not trip the check.
- This is a colour-and-shape heuristic, not face detection: it does not know where the eyes are, only where pupil-shaped red is.
FAQ
Does this tool remove the red-eye as well?
No — it only reports it. You get the centre, radius, area, average redness and a confidence score for each region, and your original file is left untouched. Feed those coordinates to your editor's red-eye tool, or use them to decide whether a photo is worth retouching at all.
It found something that isn't an eye. How do I get rid of it?
Red-eye detection is a colour-and-shape heuristic, so a round red button, a
tail-light or a bright lip highlight can score well. Three fixes, in order of
usefulness: drop Sensitivity to low, narrow the radius window with
Smallest/largest radius so only pupil-sized blobs qualify, or ignore the
low-confidence entries — the list is already sorted with the most eye-like
region first.
Why did it miss a pupil I can clearly see?
Usually the red is duller than the default thresholds expect — a partly corrected
photo, a dark-eyed subject, or the orange "amber eye" you get from an off-axis
flash. Switch Sensitivity to high. If the pupil is tiny (a face far from the
camera), also lower Smallest radius to 1 or 2. Check the warnings field: it
says explicitly when regions were skipped for being too small, too large, or not
pupil-shaped.
Is my photo uploaded anywhere?
No. The detector is compiled to WebAssembly and runs inside this page, so the image bytes are read locally and never sent to a server. You can confirm it by loading the page, going offline, and running the check.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool red-eye-checker 'url=https://example.com/input' 'sensitivity=medium' 'min_radius=3' 'max_radius=80' 'max_regions=20'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/red-eye-checker/?url=https://example.com/input&sensitivity=medium&min_radius=3&max_radius=80&max_regions=20Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.