Images
How to Reduce PNG File Size on Mac
Three things shrink a PNG: fewer pixels (resize it), fewer colors (a lossy palette tool), or a different format (JPEG, WebP or AVIF for photos). A lossless optimizer alone usually saves little, and on photos it saved about 1% in our test.
Why is my PNG so large?
PNG is lossless. It stores every pixel exactly, then packs the result. That works well for flat graphics, logos and screenshots with big blocks of one color. It works badly for photos and anything with gradients or noise, because neighboring pixels all differ slightly and there is little to pack.
We saw this with a 4032 × 3024 photo-like test image saved as PNG: 58.2 MB. The same pixels as a JPEG at sips quality 80 came to 1.35 MB. If your big PNG is a photo, the file is not badly made. It is the wrong format for the job.
What actually makes a PNG smaller?
We ran the same test PNG through each approach. The test image is synthetic, so use the ratios as a guide only.
| Method (58.2 MB original) | Result | Quality cost |
|---|---|---|
| Lossless optimizer (oxipng, level 2) | 57.6 MB (about 1% smaller) | None, pixel-identical |
| Resize to 2016 px wide (sips) | 3.47 MB | Fewer pixels |
| Reduce to a 256-color palette (pngquant, quality 30-70) | 4.6 MB | Visible banding on gradients |
| Save as JPEG (sips quality 80) | 1.35 MB | Lossy, no transparency |
Resizing is the strongest fix that keeps PNG. If you need the full pixel count and transparency, the palette route keeps both but costs color accuracy. Photos should leave PNG entirely.
How do I reduce a PNG in Preview?
Preview can resize a PNG but cannot optimize it. Open the file, choose Tools > Adjust Size…, enter a smaller width with Resample image ticked, and save with File > Export, choosing PNG. Export to a new name so the original stays.
To change format instead, set Format to JPEG in the same dialog and use the Quality slider. A PNG with transparency loses it as a JPEG: transparent areas turn solid. For the reverse direction see converting PNG to JPG on a Mac.
How do I compress a PNG from Terminal?
sips ships with macOS and handles resizing and format changes. The two optimizers below are free but need Homebrew. They are the tools we used above.
sips -Z 2000 shot.png --out shot-small.png
sips -s format jpeg -s formatOptions 80 shot.png --out shot.jpg
brew install oxipng pngquant
oxipng -o 2 --out shot-opt.png shot.png
pngquant --quality 65-80 --output shot-q.png shot.pngNote that pngquant refuses to write a file when it cannot hit your minimum quality. On our noisy test image a 65-80 range failed with exit code 99, and we had to loosen it to 30-70. That is the tool being honest, not a bug. More shell recipes are in the sips command guide.
Should I convert my PNG to JPG, WebP or AVIF?
For photos, yes. JPEG is accepted everywhere. WebP and AVIF are smaller still but not every upload form or app accepts them. Keep PNG for logos, line art, screenshots of text and anything that needs transparency or exact edges.
Our benchmark compared Smol on 24 small (768 × 512) film photographs. The same photos as PNG compressed at quality 75 were 69.2% smaller, and compressing the PNGs to AVIF at quality 65 saved 92.1%. Those images are small photos, not screenshots or your camera files, so your results will differ. Format-by-format advice is in PNG to WebP on a Mac.
When is Smol the wrong tool for this?
For one PNG, Preview resizing or the sips commands above are enough. If you need a pixel-identical file, Smol is the wrong tool: it has no lossless mode for images and always re-encodes. Use a lossless optimizer such as ImageOptim, and expect modest savings. See Smol vs ImageOptim.
Smol is for folders. Drop a mix of PNGs, JPEGs and HEIC files in, set a quality, and each file gets a smaller copy with a _compressed suffix beside the original. It runs on your Mac, uploads nothing, and also works from a Finder right-click. By default it resizes to fit inside 2000 × 2000 pixels and strips metadata, so change that if you need full resolution. It is $29 once for one Mac (buy Smol). Compare the alternatives in the best image compressor for Mac roundup.
How we checked this
Generated one 4032 x 3024 photo-like PNG and ran sips, oxipng and pngquant on an Apple Silicon Mac, recording output sizes. Smol facts come from the product fact sheet and benchmark. Facts last checked . We make Smol, so treat our claims about it with the same care as any vendor’s, and see our editorial policy.
Shrinking PNG files: common questions
Can you compress a PNG without losing quality?
Yes, but the savings are small. A lossless optimizer rewrites the file with better packing and keeps every pixel. On a photo-like PNG we measured about 1% saved. Flat graphics can do better. For big savings you must resize, reduce colors or change format.
Why is a PNG bigger than the same image as a JPG?
PNG keeps every pixel exactly, while JPEG throws away detail the eye barely notices. On photos the gap is huge: our 4032-pixel test image was 58.2 MB as PNG and 1.35 MB as a JPEG at quality 80. On flat logos and text the gap is small or reversed.
How do I make a PNG smaller and keep transparency?
Resize it, or reduce it to a 256-color palette with a tool like pngquant. Both keep transparency. JPEG does not support transparency, so avoid it for logos and cutouts. WebP and AVIF keep transparency but are not accepted everywhere, so check the destination first.
Does Preview compress PNG files?
Not really. Preview can resize a PNG and re-save it, which cuts pixels, but it has no PNG optimization or palette option. The Quality slider appears only for JPEG and HEIC export. Use Adjust Size for PNGs, or switch the format if the image is a photo.
Are macOS screenshots PNG, and can I shrink them?
By default, yes, macOS saves screenshots as PNG. Retina screens double the pixel width, which makes them large. Resizing to half the width is the quickest cut. Text-heavy screenshots stay sharp as PNG, but photos inside screenshots compress much better as JPEG.
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