How to compress images without uploading them

Compression re-encodes a picture you already opened, on the device you are using. PicZero is MSH's image toolbox. The compress page is https://msh.zone/image/compress. The pixels stay in the browser. There is no account and no per-file charge.

What the compress tool actually does

The page reads the files you chose, decodes them on a local canvas, and writes a new file in the format you picked: keep the original, JPG, WebP, or AVIF. Quality mode sets a percentage for lossy encoding. The default is 70%, and the slider runs from 10% to 100%. PNG has no quality knob. It can stay lossless, or the colors can be quantized to a smaller palette, about 128 colors by default.

The new file can only contain detail that is still in the source. If the original was already compressed, setting quality to 100% does not bring the lost detail back, and it usually makes a larger file. When the format stays the same and the result is not smaller, the tool returns the original bytes so you do not download a worse copy.

How to pick a quality

For a photo on a page or in a chat, start near 70%. Many photographs drop by about half between 60% and 75% and still look the same at normal viewing size. Screenshots, interface crops, and images with text are harsher on edges. Leave the quality higher, or use PNG quantization, instead of starting at 30%.

Run the first image in the list, look at the size before and after and at the edges of any text, then apply the same settings to the rest. A quality that suits a landscape can blur a screenshot.

When to use a target size

Use a target when a form, a shop, a signup page, or a chat app rejects the file for being too large. The default is 200 KB. You can type anything from 10 KB to 20480 KB. The tool searches for a quality close to that size. If quality alone is still over the target, it scales the long edge by 0.8 and encodes again, and it stops shrinking once the edge is about 320 pixels. A very small target will make a large photo smaller, not only blurrier.

For PNG, the levers are the palette and the dimensions, not a JPEG-style quality percentage. If you need the pixels unchanged, do not force a tiny target size.

Transparency, batches, and where the file goes

Keep PNG when you need transparency, or confirm that the WebP or AVIF path you chose still carries an alpha channel. JPG fills transparent pixels with a background color. In a batch, quality, target size, format, and rename rules are shared. Strokes you paint on one image are not copied onto the others. The longer note on folders is a folder of photos.

The original stays where it was. Download one new file, or compressed-images.zip for several. The result can stay in PicZero's list and go on to format conversion, crop, or watermark without a second trip to the disk. Removing a background is a different job: cut out locally.

What compression will not do

It will not add sharpness, restore a crop, or repair a photo beyond making the same picture into a smaller file. If the receiver also dictates a format, read convert an image locally and then decide whether to compress.