Compare Two Images Pixel by Pixel Compare two images and highlight pixel-level differences with a visual diff map.

What Is Image Difference Checker?

An image difference checker that compares two images pixel by pixel and generates a visual diff map. Differences above the threshold are highlighted in red, while similar areas are shown as dimmed original. The tool reports the percentage of pixels that differ. Adjustable threshold controls sensitivity — lower values catch subtle differences, higher values ignore minor variations. Essential for QA testing, design reviews, and spot-the-difference analysis.

Why Use Image Difference Checker?

• Pixel-level comparison with visual diff map
• Adjustable threshold for sensitivity control
• Percentage of changed pixels reported
• Red overlay clearly marks all differences

Common Use Cases

QA Testing

Detect visual regressions in UI screenshots.

Design Review

Compare design iterations to spot changes.

Photo Forensics

Detect edits or modifications in photographs.

Version Comparison

Compare before/after versions of any image.

Technical Guide

Both images are drawn onto canvas at the dimensions of the larger image. Pixel data is compared channel by channel (R, G, B). The average channel difference for each pixel is compared against the threshold. Pixels exceeding the threshold are marked red (255, 0, 0, 200) in the diff output. Matching pixels are rendered at reduced opacity (80) from the original. The diff percentage is calculated as changed pixels divided by total pixels.

Tips & Best Practices

• 1
  Lower threshold (10-20) catches subtle compression artifacts
• 2
  Higher threshold (50+) focuses on significant content changes
• 3
  Images are scaled to match — same dimensions give best results
• 4
  Download the diff map for documentation or reports

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Frequently Asked Questions

Q How does the tool handle images of different sizes?

Images are compared at the dimensions of the larger one.

Q What does the threshold setting mean?

The threshold is the average RGB difference per pixel, on a 0-255 scale.

Q How does the tool handle color sensitivity?

Compares all three color channels (R, G, B) equally.

Q Does it detect subpixel differences?

Detects any per-pixel color change above threshold.

Q What format is the diff map output?

Diff map exported as PNG with red difference overlay.

About This Tool

Image Difference Checker is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.