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Equalize image area online

Use an online histogram equalizer to equalise a selected image area. Move and resize the box, preview local contrast changes, and download PNG.

What is area histogram equalization?

Area histogram equalization is a local contrast enhancement method. It calculates a histogram and cumulative distribution from a selected zone, then remaps tones only in that zone to spread brightness values more evenly. Compared with full-frame equalization, this histogram equalizer approach gives finer control when only part of an image needs contrast recovery.

Area equalization features

Local histogram equalizer workflow with draggable selection.

  1. Draggable area selector: Choose exact region with move and resize handles.
  2. Local histogram CDF: Builds equalization curve from selected zone only.
  3. Selective application: Applies remap inside area while preserving outside pixels.
  4. Auto preview: Result refreshes whenever the area changes.
  5. PNG download: Export equalized image as PNG.

How to equalize an image area

Quick steps for local equaliser adjustments.

  1. Upload image: Drop or select PNG, JPEG, WebP, or GIF.
  2. Set area: Drag and resize the selection box over the region you want to adjust.
  3. Review preview: Compare local contrast changes in the output panel.
  4. Download PNG: Save the processed image when it looks right.

Tips for better local equalization

Improve local equaliser results.

  1. Keep area focused: Include the subject region, avoid unrelated extremes in the same box.
  2. Test different area sizes: Smaller zones create stronger local adaptation.
  3. Compare with global equalize: Use /equalize-image if the whole photo needs correction.

Great for

When local equalization is useful.

  1. Faces in backlit photos: Increase local detail without overprocessing sky/background.
  2. Documents and labels: Improve legibility in a specific area only.
  3. Product close-ups: Enhance texture on target region while keeping scene balance.

Why use this tool

Targeted contrast control in-browser.

  1. Localized edits: Avoid global tone shifts when only one zone needs recovery.
  2. Fast iteration: Drag the area and see instant updates.
  3. Private workflow: No file upload required.
  4. Free PNG export: Download final output with one click.

Technical details

Implementation summary.

  1. Per-channel method: Equalizes R, G, B independently using area histogram CDF.
  2. Bounds handling: Selection is clamped to canvas boundaries.
  3. Rendering: Canvas 2D pixel operations via getImageData/putImageData.
  4. Output format: PNG download only.

Frequently Asked Questions

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