Image Compressor

What is an image compressor?

An image compressor makes a picture’s file smaller by re-saving it at a lower quality, so it downloads faster and takes up less space. This tool re-encodes whatever image you choose as a JPEG at a quality you pick, shows you the original size, the new compressed size, and the percent saved, and downloads the smaller file. Everything happens locally in your browser, so the image is never uploaded to a server.

It is the quick way to turn a heavy phone photo or screenshot into something light enough to email, attach to a form, or post on the web without waiting on a slow upload.

What does this tool do?

You choose an image and set a quality value between 10% and 100% with the slider (it starts at 80%). When you click Compress & download, the tool re-saves the picture as a JPEG at that quality, immediately downloads the result as a file named like photo-compressed.jpg, and fills in three boxes: Original, Compressed, and Saved.

The first two show file sizes in kilobytes (KB), and Saved shows the percentage reduction. Lower quality means a smaller file but softer detail; higher quality keeps detail but saves less. The pixel width and height never change — only the file size does.

How does it work?

The method is JPEG re-encoding on an HTML canvas, not a math formula. Here is the exact sequence:

1. The tool reads your chosen image and loads it at its natural pixel size.
2. It creates a canvas the same width and height as the image, fills it with white, then draws your image on top. The white fill matters because JPEG has no transparency: any see-through pixels (common in PNGs) land on solid white.
3. It exports the canvas as a JPEG blob at the quality you selected, where the slider value is divided by 100 to give a quality from 0.10 to 1.00.
4. It downloads that blob and reports the sizes.

A few terms, defined: quality is how much detail the JPEG keeps when it compresses; it is not a percentage of the file size. KB (kilobyte) here means 1024 bytes — the tool divides the byte count by 1024 and rounds to one decimal. Saved is calculated as one minus (compressed size divided by original size), turned into a percent and rounded; if a re-encode ever comes out larger than the original, Saved is clamped to 0% rather than shown as a negative number.

Examples

Each example matches exactly what the widget does — re-encode as JPEG at the chosen quality and report the sizes. Real numbers vary with the photo, so these show the typical pattern.

Example 1 - a 2 MB photo at 80% quality. You pick a 2 MB photo and leave the slider at 80%. The output often drops to a few hundred KB — well over half saved — while looking essentially identical on a screen. Original might read 2048.0 KB, Compressed 350.0 KB, and Saved roughly 83%.

Example 2 - the same photo at 60% quality. Drop the slider to 60% and the file shrinks further, but you start to see softer detail and faint blocky patches in skies and smooth gradients. It saves more space than 80% at the cost of sharpness — a fair trade for a thumbnail, a poor one for a print.

Example 3 - a transparent PNG. You pick a PNG logo with a transparent background. Because the output is JPEG, the transparency is flattened to white, so the saved file shows your logo on a solid white rectangle. If you need to keep transparency, JPEG is the wrong target format.

Example 4 - an already-small JPEG. You pick a 90 KB JPEG that is already compressed and choose 80%. There is little left to remove, so the result may be only slightly smaller, about the same, or even a touch larger — in which case the tool reports 0% saved.

Quality settings reference

This table is a practical guide to the slider. Exact sizes depend on the image, so the size column shows the typical direction, not a promise.

Quality	Typical look	Best for	Relative file size
90-100%	Near-identical to original	Archiving, prints, hero images	Largest
75-85%	No obvious loss on screen	Web pages, email, social posts	Much smaller
60-70%	Slightly soft, minor artifacts	Thumbnails, previews, drafts	Smaller still
10-50%	Visibly blocky and soft	Tiny placeholders, heavy size limits	Smallest

For most photos, 80% is the sweet spot: a large size cut with no obvious quality loss.

Common uses

Compressing images comes up almost anywhere a file is too big:

• Web and blog work - shrink photos so pages load fast and pass speed checks, since smaller images are the single biggest page-weight win.
• Email and uploads - get a photo under an attachment or form size cap (for example a job portal that rejects files over a few hundred KB).
• Social media and messaging - post or send pictures without long uploads on a slow connection.
• Storage cleanup - reduce a folder of phone photos before backing them up or sharing a batch.
• Documents and slides - lighten images before dropping them into a PDF or presentation so the final file is not bloated.

Tips and common mistakes

A few details get you the best result:

• Start at 80%, then adjust. It usually gives a big saving with no visible loss. Only drop lower if you still need a smaller file and can accept softer detail.
• JPEG is lossy and one-way. Each compression throws away detail permanently. Always keep your original and compress a copy — re-compressing an already-compressed image just degrades it further.
• Do not use it on transparent graphics. PNG logos, icons, and cut-outs lose transparency to a white background here. Keep those as PNG.
• Compression is not resizing. This tool keeps the same width and height. If a photo is far larger than where it will be shown, resizing the dimensions first saves even more.
• Tiny gains are normal on small files. Already-optimized or very small images have little to remove, so do not expect a big cut every time.

Limitations and notes

This tool always outputs a JPEG, no matter what you put in, which is why transparency is flattened to white and the download ends in .jpg. It changes only the file size, never the pixel dimensions. Sizes are shown in KB by dividing bytes by 1024, so they are close estimates rather than byte-exact figures, and the Saved figure never goes below 0%. It accepts any image your browser can read and rejects non-image files with a clear message. There is no fixed file-size cap, but very large images are limited by your browser’s memory.

Most importantly, the whole process runs privately in your browser. Your image is drawn on a canvas and re-encoded in JavaScript — it is never uploaded, logged, or stored, which makes it safe for personal or confidential photos and usable offline once the page has loaded.

To resize before you compress, embed the result, or clean up text, pair this with the image resizer, the image to base64 converter, and the case converter, and browse the full Image & PDF tools collection.