How to batch-compress website images: unified size, format, and ZIP download flow

When batch compression fits

Batch compression is suitable for a group of images with similar uses: article images, product-list images, portfolio thumbnails, or backend assets waiting for upload. Its advantage is unified handling, reducing the time spent repeating settings image by image. The current tool shows each image’s original size, output size, output dimensions, status, and download entry.

If every image has a different target, such as the first needing 80KB and the second needing 300KB, the batch tool is not the best entry point. It has no target KB field and no per-file settings; all images share the output format, quality, and maximum size.

Open batch image compressor

How to choose shared settings

Choose the output format first. JPEG has broad compatibility and fits photos and images that do not need transparent backgrounds; WebP is often used for web assets, but whether the receiving platform and older environments support it must be confirmed separately. The batch tool supports JPEG and WebP output; if the browser cannot export the selected format, the corresponding row shows a failure.

Then set maximum size. Here, maximum size limits the longer edge, not exact width and height: a 2400 × 1600 landscape image set to 1200px becomes about 1200 × 800, and a 1600 × 2400 portrait image becomes about 800 × 1200. Finally adjust quality. Lower quality usually saves more size, but detail loss also becomes more obvious.

Test WebP output on one image

Recommended flow

Before batch processing, group images by use. Large images, thumbnails, transparent graphics, and screenshots should not be mixed in the same batch because they tolerate quality and format changes differently. Using one setting for a group of similar images makes results more controllable.

After selecting files, compress a small sample first and check output dimensions and sizes in the result table. If many rows say “Ready, but not smaller than the original,” those images may already be small enough, or the current format may not suit further compression. When more than one file is complete, you can download a ZIP; the ZIP is only convenient packaging and does not mean image pixels are compressed again.

1. Group by use, and do not mix transparent images with ordinary photos in one batch.
2. Choose JPEG or WebP output and set the longest-edge cap.
3. Run one pass at medium quality first and inspect each row’s status.
4. After confirming multiple results are usable, download individual files or the ZIP.

Hypothetical example

Suppose you need to organize 30 article cover images from different phones, with very different dimensions and file sizes. You can put them in one batch, choose JPEG output, set maximum size to 1600px, and use medium-high quality. After compression, inspect the table to confirm large images have been reduced to suitable dimensions and small images were not enlarged.

If several of them are transparent PNG icons, do not export them together with photos as JPEG, because transparency will become a white background. Icon assets can be handled separately with the format converter or resizing tool, or converted to WebP after you confirm the site supports it.

Convert format for one image

Limits and decision boundaries

The batch tool decodes, scales, re-encodes, and creates a ZIP in the browser tab. It skips or marks rows it cannot process and continues with other files. Input and output are both for static images; animated images do not preserve animation, and metadata or color profiles are not preserved as editable objects.

If a website has a strict KB cap for each image, using the batch tool to standardize dimensions first does not guarantee compliance; images still over the limit need the target KB tool one by one. If a website requires exact pixels, such as all thumbnails being 800 × 450, batch compression’s maximum size is not exact dimensions, so use the resizing tool first.

Handle exact pixel dimensions

FAQ

Will batch compression make every image the same size?

No. It processes each image with the same format, quality, and maximum size, but different image content produces different output sizes.

Does ZIP download compress the images again?

No. ZIP is mainly used here to package multiple generated output files for one download, and should not be understood as additional image-quality compression.

Can I select a folder directly?

The current tool processes images through multi-file selection and does not provide folder import. Select the image files you need in the file picker first.

References

• HTMLCanvasElement: toBlob() method | MDN
• Image file type and format guide | MDN
• WebP documentation | Google for Developers