Compress PNG with transparency: why dimensions can change
A smaller PNG is useful for sharing a screenshot or placing a transparent graphic on a website. But reducing bytes and preserving every pixel are different goals. This guide explains the current WeLoveConvert image compressor so you can choose a setting without accidentally making a logo or small text too small.
This guide describes format capabilities and settings available in different programs. In WeLoveConvert you select the output format and, for supported images, quality. Codec, bitrate, lossless WebP mode and TIFF page selection are not available in the interface. Compare the result and keep your original.
What the PNG slider actually does
The image compressor keeps PNG output and draws the image on a transparent canvas. For a file identified as image/png, the percentage sets the width and height to that fraction of the original, with a minimum scale of 10%. It is not a PNG compression-level control. A setting below 100% resamples the image and therefore changes its pixels. Keep an untouched original before experimenting.
A worked dimension example, not a size promise
For an illustrative 1200 × 800 PNG, 75% produces a candidate of 900 × 600 pixels; 50% produces 600 × 400. The latter has one quarter of the original pixel count, not necessarily one quarter of the file size. Image detail, transparency and encoding affect the number of bytes. These dimensions follow the implementation formula; they are not measured exports or a benchmark. The compressor returns the original file if its candidate is not smaller, so the saved result can retain the original dimensions.
Choose, compress and verify
- 1
Inspect the original
Note its pixel dimensions and file size. Keep a backup. Decide whether small text, a logo edge or a minimum upload resolution must stay readable.
- 2
Select a PNG
Open the image compressor, select the file and continue to configuration. Check the PNG notice next to the quality slider.
- 3
Choose a cautious setting
Start at 100% when dimensions must stay unchanged. If a smaller image is acceptable, lower the percentage gradually and keep the tab open during processing.
- 4
Check the saved result
Download the result and inspect actual dimensions, file size and transparency in an image editor. Compare text at 100% zoom and view transparent edges against light and dark backgrounds.
Lossless format does not mean lossless resizing
The W3C PNG specification defines PNG as a lossless image format with transparency support. That describes encoding the supplied pixels. Resizing before encoding still removes detail. This workflow also does not guarantee preservation of embedded metadata, color profiles or animation. Do not replace a print master, signed asset or archival image just because the preview looks similar.
When PNG, WebP or JPG is a better choice
Keep PNG when the destination requires it, when sharp screenshot text matters, or when you need transparent graphics with predictable compatibility. PNG to WebP is another option for supported web destinations and retains transparency in the current canvas workflow; compare the saved result because encoding can be lossy. PNG to JPG flattens transparency onto white. It can suit an opaque photograph, but it cannot preserve a transparent logo.
Troubleshoot unexpected results
If the download is unchanged, the candidate may not have been smaller than the original. There is no guaranteed reduction percentage. If text becomes blurry or dimensions fall below a platform minimum, return to the original and raise the setting. If the file is not recognized as PNG, avoid forcing it through another extension: re-export a genuine PNG with an image editor. If processing stops on a large image, try a smaller copy and close unnecessary tabs.
Choosing an export for a website
Check how large the image will actually appear before shrinking it. A 600-pixel image displayed at 600 CSS pixels may be too soft on a high-density screen. Keep sufficient source pixels for the intended display density, then compare the downloaded bytes. For a tiny screenshot containing text, cropping in an editor can be more useful than reducing the entire image. This compressor does not provide cropping, a target-KB field or a same-dimension PNG optimizer.
Frequently Asked Questions
Can I compress PNG without changing its dimensions?
Try 100%, but this tool does not guarantee a smaller file at the same dimensions. Use a dedicated lossless PNG optimizer when exact pixels and dimensions must be preserved.
Does a transparent preview prove transparency was preserved?
No. Open the saved file and inspect its alpha channel or view it on two different backgrounds. Do not rely only on the website preview.
Will 50% halve the file size?
No. For recognized PNG inputs it halves width and height for the candidate. Byte size depends on content; the original is kept if the candidate is larger or equal.
Choose the smallest result that still meets your real requirements. Keep the original, check the downloaded file, and treat a lower PNG percentage as a resolution decision rather than a promise of lossless byte reduction.