How to Compress a PNG Without Losing Quality (or Transparency)
By Tooldesk team · · 3 min read
To compress a PNG without visible quality loss, reduce its colours to a smart palette and save it as a PNG again. That keeps transparency and usually cuts the size by half or more. Open our Compress Image tool, leave the output format on Same as original, and set quality to around 75%. At 90% or above, the tool repacks the PNG losslessly instead, so every pixel stays identical.
Why PNG files are big
PNG is a lossless format: it stores every pixel exactly. That’s perfect for screenshots, logos, icons and graphics with sharp edges and flat colours. It’s a poor fit for photos, where millions of slightly different colours make the file huge. A phone photo saved as PNG is often three to five times bigger than the same photo as a JPG.
Two ways to compress a PNG
Lossless: smaller file, identical pixels
The image data is re-packed more efficiently. Nothing changes visually, and the file shrinks a little, often 5–20% depending on how the original was saved. Choose a quality of 90% or more in our tool for this mode.
Palette quantisation: much smaller, looks the same
Most graphics use far fewer colours than PNG allows. Quantisation picks the best 256 colours (or fewer) for your image and maps every pixel to the nearest one. Dithering mixes neighbouring colours so gradients stay smooth. Transparency is kept. This is how popular “tiny PNG” services work, and it often cuts the file by 60–80% for screenshots and graphics.
In our tool, a quality around 75% uses 256 colours. Lower quality settings use fewer colours for even smaller files.
When to switch formats instead
| Image | Best format | Why |
|---|---|---|
| Logo, icon, UI screenshot | PNG (quantised) | Sharp edges and flat colours, often needs transparency |
| Photo with no transparency | JPG or WebP | Much smaller than PNG at the same visual quality |
| Photo or graphic with transparency, for the web | WebP | Supports transparency and is smaller than PNG |
| Image for print or further editing | Original PNG | Keep the lossless master |
To convert, use PNG to JPG or PNG to WebP. Remember that JPG has no transparency: transparent areas become white.
Steps
- Open Compress Image.
- Add your PNG files. You can add many at once.
- Keep Output format on Same as original to stay with PNG.
- Set the quality:
- 90–95% for lossless repacking.
- 70–80% for the best balance on graphics and screenshots.
- 50–60% for the smallest files where small colour shifts are acceptable.
- Optionally set Max width or height if the image is larger than it will ever be displayed. A 4000 px screenshot shown at 1000 px wide wastes most of its bytes.
- Select Compress images and compare the before-and-after sizes.
If a compressed file would come out bigger than the original, the tool keeps the original instead.
Checking for quality loss
Open the original and the compressed file side by side at 100% zoom. Look at:
- Gradients such as sky or shadows: they should not show visible bands.
- Small text in screenshots: edges should stay crisp.
- Transparent edges of logos: there should be no dark or white fringe.
If you see banding, raise the quality a little and compress again.
Questions people ask
Does compressing a PNG reduce quality?
Lossless repacking doesn’t change any pixel. Palette quantisation does change colours slightly, but at 256 colours with dithering the difference is very hard to see on graphics and screenshots.
Why is my PNG still large after compression?
It is probably a photo. Photos have too many colours for a palette to capture well. Convert it to JPG or WebP for a much smaller file.
Will my transparent background stay transparent?
Yes, as long as the output stays PNG or WebP. Converting to JPG fills transparent areas with a solid colour.
How do I reduce an image to an exact size like 100 KB?
Use the Target size (KB) mode. Our guide on reducing image size in KB covers form limits for photos and signatures.