Image Compressor

What image compression actually does

Compression is re-encoding. The image is drawn onto a canvas at the width you ask for and saved again at the quality you choose, which produces a genuinely smaller file. That is why the two things people usually try instead do nothing at all: dragging a photo smaller inside a document or a slide deck only changes how it is displayed, and renaming a file from .png to .jpg only changes the label. The pixel data on disk is identical in both cases. Two things really shrink a file: throwing away resolution you were never going to use, and letting the encoder discard detail your eye cannot pick out.

Where it pays off:

• Page speed. On most pages the largest image is the Largest Contentful Paint element, so every kilobyte you remove from it is time the visitor does not spend waiting.
• Social posts. Platforms cap the dimensions they will display and re-encode anything larger, so uploading a 4000 pixel wide photo wastes your upload and hands the platform a decision you could have made yourself.
• Email attachments. Mailbox providers commonly cap a message at around 25 MB including encoding overhead, and a handful of phone photos passes that easily.
• Storage and mobile data. Smaller files mean more room in a cloud plan and less data burned when someone opens your page on a phone.

Which output format to pick

• JPG: the safest choice for photographs. Lossy, but at 80 percent quality the difference is hard to see on a normal screen, and everything that opens images can read it.
• WebP: Google reports lossy WebP files are about 25 to 34 percent smaller than comparable JPEG files, and it supports transparency. The default choice for the web if you do not have to support very old software.
• PNG: lossless and keeps a transparent background. Right for logos, icons, diagrams and screenshots of flat colour; wrong for photographs, where it will usually be the biggest of the three.

Settings worth starting from

These are starting points, not rules. Photographs with a lot of fine texture, such as foliage or fabric, show artefacts sooner and want a higher quality number; flat illustrations survive much lower settings. Check the result at full size before you commit to a batch of a hundred.

How to compress a batch of photos

1. Set the quality, the output format and the maximum width first. The settings are applied at the moment an image is added.
2. Drag the whole batch onto the upload area, or use the file picker and select several files at once. Anything over 10 MB is skipped with a notice; more than 50 files at once only warns you that it may be slow.
3. Wait for the progress counter. Each file is processed on its own, so one that cannot be read is marked as failed on its row while the rest carry on.
4. Read the saved total above the list to judge whether the settings are right. Change the quality, the width or the format and the images already in the list are compressed again with the new settings, so there is no need to clear and re-pick them.
5. Download the rows you want one at a time, or press Download all as ZIP to take the whole batch in one file.

How to get a photo under a size limit

A form, a submission system or a client mailbox gives you a ceiling, say 2 MB per image. There is no automatic mode that hits a target size, but this order gets there in two or three tries:

1. Change the maximum width first. It has by far the largest effect, and most uses need nowhere near the original resolution: 1920px is plenty for a full width image on a page, and 1600px is generous for a document or a form.
2. Choose JPG or WebP. A photograph saved as PNG is almost always bigger than either.
3. Start the quality at 80 percent and step down by about 10 percent at a time, watching the compressed size in the list. Below roughly 50 percent the blocking usually becomes visible.
4. Let the list finish re-compressing before you download. The file extension follows the format the browser actually produced, so you will not end up with JPG data in a file named .webp.
5. If it still will not fit, the original is probably very large, for example a 4000 pixel wide phone photo. Go back to step one and cut the width again.

Getting the compressed files where you need them

• One file at a time: the download button on each row saves it as original-name-compressed.ext, so the original is never overwritten and you can keep both side by side to compare.
• The whole batch: Download all as ZIP packs every successful row into toolmaple-compressed-date.zip. Duplicate names are numbered automatically, so nothing inside the archive overwrites anything else.
• Attaching or uploading: unzip and drag the files straight into your mail client, a form or a cloud drive. On a phone the download lands in the system Downloads folder, and you pick it from there in the upload dialog.
• Changing format rather than size: if you only need JPG to PNG or PNG to WebP, use the image converter. To embed an image directly in CSS or HTML source, use image to Base64.
• Close the tab and it is gone: the list and the compressed results live only in this tab. A refresh means compressing again, so download before you leave.

Where behaviour differs by browser and platform

• An output format the browser cannot encode: the HTML specification says the canvas falls back to PNG when the requested type is not supported. So if you pick WebP and the file barely shrinks, switch to JPG and try again. This tool calls canvas.toBlob(callback, type, quality), the same API described on MDN.
• HEIC from an iPhone: whether it can be compressed depends entirely on whether your browser can decode that format, and many cannot. Files that fail are marked on their own row. Setting the iPhone camera to Most Compatible so it records JPEG is the easiest way around it.
• Social platforms: uploads are normally re-encoded by the platform itself, so compress to the dimensions and size it asks for and stop there. Squeezing further only means your already degraded image goes through a second lossy pass. Published limits change, so check the current figures with the platform.
• Transparency: saving a PNG as JPG loses the alpha channel. The specification has the browser flatten the transparent pixels onto a solid background, commonly black, which is easy to miss on a logo until it is already in the layout. Output PNG or WebP when you need transparency.
• Desktop versus phone: the work happens on your device, so the same batch is noticeably slower on an older phone, and a very large image can exhaust the memory a mobile browser allows a tab. Work in smaller batches on mobile.

Limits worth knowing

Nothing is uploaded. The files you pick are re-encoded by the browser canvas on this device, with no network request in the process, so the page works offline. Scanned documents and screenshots containing personal data can be handled here without them reaching anyone.

• Lossy compression cannot be undone. Compressing an already-compressed file again only degrades it further, so always go back to the original when you change settings rather than feeding an output back in.
• The maximum width only shrinks, never enlarges. Entering a number larger than the original will not sharpen anything; the image keeps its own width.
• The output is a redrawn image, so EXIF data such as the capture time and GPS location is dropped. That is a feature when you are sharing a photo and a problem when you need an archive copy.
• Files over 10 MB are skipped, and while more than 50 at once is allowed, everything runs in this tab’s memory. Split very large batches.
• Colour management is left to the browser. An image in a wide gamut profile may come back looking slightly different, so check a colour critical image before publishing it.