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image-format-batch-converter

A batch image format converter takes many images at once and converts them to a different format in a single operation, producing a downloadable ZIP. The ZTools Image Format Batch Converter supports JPG, PNG, WebP, AVIF, GIF, and BMP both as input and output, with per-format quality settings and optional resize-to-max-dimension. Drop in dozens of files (or a whole folder via drag-drop), choose the target format, click Convert, and download a ZIP with everything renamed and re-encoded. All in the browser; nothing uploaded.

Use cases​

Converting an entire photo album from JPG to WebP for the web​

Drop your vacation-2026/ folder, choose WebP at quality 85, get a ZIP back with every photo at ~30% smaller file size. Drop the ZIP into your blog's /images/ folder and update the <img> tags. Substantially improves Largest Contentful Paint at no visual quality cost.

Migrating PNG screenshots to WebP for a docs site​

Documentation sites often have hundreds of PNG screenshots. Batch-convert to WebP for 50-70% size savings and faster page loads. Maintain a PNG fallback for old browsers via <picture> markup.

Converting heritage TIFF or BMP archives to modern formats​

Old archive formats (TIFF, BMP) are massive and poorly supported. Batch-convert to JPG or PNG for everyday use; keep the originals for archival.

Standardizing user-uploaded images on a single format server-side​

Front-end pre-processing: when a user uploads any image, batch-convert to a standard format (typically WebP) before sending to the server. Reduces server-side complexity and bandwidth.

How it works​

  1. Drag-drop multiple images or a folder — Up to ~100 files at once on a desktop browser. The file list shows each input with a small thumbnail.
  2. Choose target format and quality — JPG, PNG, WebP, AVIF, GIF, BMP. JPG/WebP/AVIF have a quality slider (0-100); PNG/GIF/BMP are lossless.
  3. Optionally enable resize-to-max — Cap output dimension (e.g., max 1920px on the longest edge). Source images smaller than the cap are left untouched.
  4. Click Convert — Each image is loaded into a canvas, re-encoded in the target format, and added to an in-memory ZIP using JSZip. Progress bar shows completion.
  5. Download the ZIP — Single download contains every converted file with the original filename + new extension. Originals on disk untouched.

Examples​

Input: 50 JPG photos averaging 3 MB each → WebP @ quality 85

Output: 50 WebP files averaging 1.1 MB each (≈63% size reduction)

Input: 100 PNG screenshots → AVIF @ quality 80

Output: 100 AVIF files (≈40% the size of WebP, ≈25% the size of PNG)

Frequently asked questions​

How many files can I batch-convert at once?

Up to ~100 files comfortably on a modern desktop browser, limited by available memory. For thousands of files, split into chunks or use a desktop tool like ImageMagick.

Will my images be uploaded?

No. All conversion happens in your browser via the Canvas API; the ZIP is built in memory by JSZip. Disconnect from the internet after page load and the tool still works.

What's the best format for the web in 2026?

AVIF for the smallest size; WebP as a fallback for browsers without AVIF support; JPG/PNG as final fallbacks for very old browsers. Use <picture> to serve all three from a single tag.

What quality setting should I use?

JPG: 85 is a strong default (visually lossless for most photos). WebP: 80-85. AVIF: 75-80 (AVIF is more efficient than WebP at the same quality number).

Does conversion preserve transparency?

PNG → WebP/AVIF: transparency preserved. PNG → JPG: transparency replaced with white (JPG has no alpha channel). The tool warns when this would happen.

Are EXIF metadata preserved?

No — Canvas-based conversion strips EXIF. For EXIF preservation use a desktop tool. (Privacy benefit on the web: stripping EXIF removes embedded GPS coordinates from photos.)

Tips​

  • Default to WebP for web images — best compatibility/size tradeoff in 2026.
  • Use AVIF for the cutting edge — pair with <picture> for fallbacks.
  • For batch-resizing along with conversion, enable the max-dimension cap to avoid uploading 4000px photos.
  • Run a small batch first (5 files) to verify quality before committing to a 100-file batch.

Try it now​

The full image-format-batch-converter runs in your browser at https://ztools.zaions.com/image-format-batch-converter — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-05 · Author: Ahsan Mahmood · Edit this page on GitHub