Bulk Image Compressor

How do I compress a batch and check the actual savings?

Choose your images, set Quality or Target Size, and run the button showing your pending image count. A batch of three files shows Compress 3 images. Finished rows show the original size, exported size, and a rounded savings badge. Click a finished thumbnail to open its before/after comparison, then download individual results or the ZIP.

For a worked example, suppose three source images each contain 1,024,000 bytes and their exported copies contain 307,200, 409,600, and 512,000 bytes. These are illustrative measured outputs, not predictions for a quality setting. The tool calculates each reduction as round((original - compressed) / original × 100), then prevents negative savings from appearing in the badge.

Example savings for three completed images

Image	Original bytes	Exported bytes	Savings badge
Product photo	1,024,000	307,200	70%
Detail photo	1,024,000	409,600	60%
Packaging photo	1,024,000	512,000	50%

The batch totals are 3,072,000 original bytes and 1,228,800 exported bytes: a 60% reduction. Batch savings use summed file sizes rather than an average of row percentages. Wait until every file finishes before judging the summary: its original total includes the whole list, while its compressed total includes only available results. The ZIP is a separate package; the summary totals image outputs rather than archive size.

How do Quality and Target Size differ?

Quality mode starts at 80% and passes the selected percentage to the image encoder. It controls encoding quality, not a promised reduction percentage: 80% quality does not mean an 80% smaller file. The presets are Print at 90%, Web at 80%, Email at 70%, and Micro at 50%. Treat these as starting points and inspect text, edges, gradients, and fine detail in your actual images.

Target Size starts at 200 KB and converts KB to bytes by multiplying by 1,024. For JPEG and WebP it searches quality between 10% and 100%, using up to 10 iterations. It stops early when an output at or below the target is within 5% of it. If none fits, a final attempt at 10% quality is returned, even if it remains too large. This is a size-budget aid, not a guarantee of an exact size.

The editable target maximum is based on the smallest input: its size in whole KB minus one. Separate unusually small files from a batch of large photographs if that restricts your target choice. There is no resizing control here. If dimensions are unnecessarily large, use Bulk Image Resizer before compression, then check the resulting file sizes again.

Which formats can I keep or convert?

The file picker lists JPEG, PNG, WebP, and AVIF. Output format offers Original Format, JPEG, WebP, PNG (lossless), and AVIF in Quality mode. Original Format resolves each input independently, so a mixed batch does not have to become a single format. Choosing a named format applies that output choice to the batch.

PNG output ignores the quality slider. Re-encoding a PNG does not guarantee a smaller file, so test a different format when file size matters more than retaining PNG. Use PNG to WebP for a dedicated conversion workflow. AVIF export depends on the browser's encoder; selecting it is not a promise of a particular compression ratio or universal encoding support.

In Target Size mode the format list retains Original Format, JPEG, and WebP. There is an important mixed-batch distinction: with Original Format selected, only JPEG and WebP files enter the target-size search. PNG and AVIF files follow ordinary conversion using their effective quality, with PNG ignoring that value. Choose JPEG or WebP explicitly if every image must attempt the same size budget.

How can I adjust one image without recompressing everything?

Each row has a Q percentage control on wider screens. Open it to reveal a 1–100 quality slider. An individual override takes priority over global quality; Reset removes that override and returns the row to the shared setting. For a completed image, click Re-compress beside the slider to regenerate that file. Quality overrides affect quality-based conversion, not the JPEG/WebP target-size search.

Changing a global setting enables Re-compress All with the completed count once there are no pending files. Each attempt reads the stored original File rather than using the previous compressed result as its input. This lets you compare alternative settings without repeatedly encoding an already exported copy. For a single-image workflow, Image Compressor is another option.

What does no change mean, and why should I preview the result?

A no change badge is not a byte-for-byte identity check. The row rounds percentage savings to the nearest integer and clamps any negative reduction to zero. A slightly smaller output and a larger output can therefore carry the same badge. The result is not automatically replaced with your original when compression increases size.

Read both sizes and use the thumbnail comparison before downloading. PNG is lossless at the pixel encoding stage, but changing to a lossy format or lowering quality can change visible detail. JPEG does not retain transparency, and this interface has no background-color selector. Check transparent assets carefully before converting them to an opaque format. Keep your source files for later editing.

Where are images processed, and what are the practical limits?

The compression path uses createImageBitmap to decode a local file, draws it onto a canvas, and exports a new image through the browser encoder. It uses OffscreenCanvas when available and an HTML canvas fallback otherwise. There is no upload step in that processing path. The exported image is regenerated from pixels rather than copying source EXIF metadata into the output.

The interface advertises up to 50 images and hides Add more at that count. It does not enforce that count on the initial selection or validate a 50 MB per-file ceiling. Available memory and browser decoding support remain practical constraints. Processing is sequential, but selected originals and previews remain in memory alongside exported files. Start smaller for large photographs, check any row errors, and use Clear or Compress more images after saving your results.

How do I save, name, or share the finished batch?

Output names start with the original filename stem plus _compressed. Edit the name in a row before downloading; the tool supplies the extension for the selected format. The batch ZIP is named compressed-images.zip and includes successfully completed results. Check the completed count if a file failed rather than assuming every selected input is present.

Individual download buttons save single results. ZIP download groups the batch, while Share uses the device's sharing interface where file sharing is supported. Sharing a batch passes the ZIP rather than a set of separate image attachments. Save the files you need before clearing the list, and verify any destination's format and byte limit against the actual exported files.