FileDial › Guides › Photos and images
How to compress PNG files on a Mac
By Himanshu Ranjan · Updated 8 November 2026
To shrink PNG files on a Mac, select them in Finder and run Compress › Compress in FileDial, which saves a smaller copy that looks the same. If that is not small enough, reduce the pixel size with a Resize tool, or convert photographs to JPG or WebP. Check the result card for before and after sizes.
Why PNGs get big
PNG uses lossless compression: a predictive filter followed by DEFLATE, according to Wikipedia. Nothing is discarded, so photographs and screenshots with gradients, noise or many colours produce large files. Flat graphics with few colours compress very well, especially as 8-bit palette images, which store up to 256 colours.
Retina screenshots add to it. A full-screen capture on a high-density display has many pixels, and a PNG stores all of them.
Compress with FileDial
Compress › Compress makes a smaller copy that FileDial describes as looking the same. The result is a new file beside the original, and the card shows the size before and after, so you know exactly what you saved without us quoting a number that depends on your pictures.
- Select the PNG files in Finder.
- Hold the right Option key to open the dial, or right-click and choose Open in FileDial.
- Choose Compress, then release on Compress › Compress.
- Read the before and after sizes on the result card, and use the new copy.
- If you need a hard limit, use Compress › Compress under 1 MB or Compress › Compress to size…
Three ways to go smaller, in order of cost
First try compression at the same pixel size, which keeps the picture as it is. Second, reduce the pixel dimensions with Resize › Resize to 50% or Resize › Resize to 1080 px; a smaller picture needs fewer bytes, and most web slots do not need a 4000 pixel image. Third, change the format.
If the PNG is a photograph, JPG or WebP will be far smaller. Use Convert › Convert to JPG or Convert › Convert to WebP. Be aware of what you give up: JPG is lossy and has no transparency, and the FileDial note for WebP says metadata is not kept.
- Screenshots with text: stay with PNG, compress or resize.
- Logos and icons with transparency: stay with PNG, or WebP.
- Photographs saved as PNG: convert to JPG or WebP.
When PNG should stay PNG
Keep PNG for anything with transparency, sharp text, UI captures and graphics headed for further editing. Converting a UI screenshot to JPG introduces fuzzy halos around letters, which is the reason PNG exists for that job.
Also keep an untouched master. Compress copies and keep the original in case you need to edit again.
Screenshots specifically
Screenshots deserve their own rules because they are mostly PNG and often huge. A full-screen capture from a high-density display can be several megabytes, and a folder of them swallows disk space. Two sensible steps help. First, capture only the area you need rather than the whole screen. Second, resize screenshots that will sit in a document to the width they will be shown at.
Keep fine text legible. If you convert a screenshot to JPG to save space, check the text at normal size, because JPG blurs sharp edges. If text looks smudgy, go back to PNG and use resize and compression instead.
For long-term storage, consider archiving old screenshots. FileDial's Archive › Make ZIP and Archive › Make 7Z write new archives beside the originals, though PNGs are already compressed so archiving mainly tidies rather than shrinks.
- Capture only what you need.
- Resize to the display width.
- Check text after any conversion.
Mistakes to avoid and what to pick
Do not expect miracles from compression alone on photographic PNGs. If the size is very large, reduce dimensions or change format. Do not convert transparent PNGs to JPG, which replaces transparency with a solid fill. And do not compress the only copy of something you may need to edit again.
Preview is fine for one or two files, particularly if you only need to lower dimensions through Tools > Adjust Size. FileDial is the better pick for folders, for target sizes such as Compress › Compress under 500 KB, and for before and after reporting. When file size matters for a website, converting to WebP or AVIF will beat PNG compression for photographs, but keep PNG for logos, text and transparency.
Without installing anything
On macOS, Preview can export PNG but does not offer a PNG quality slider. Its Adjust Size dialog lets you lower the dimensions, and Apple notes that selecting Resample image with a lower resolution value reduces file size. That is a legitimate built-in route for one or two images.
FileDial is for folders and for predictable results. It works offline and never uploads your files.
Questions
Can I make a PNG smaller without losing quality?
PNG is lossless, so the format itself keeps all the pixels. FileDial's Compress › Compress makes a smaller copy that it describes as looking the same. For bigger savings, reduce the dimensions or convert photographs to JPG or WebP, which are lossy.
Why is my screenshot PNG so large?
Screenshots on high-density displays contain many pixels, and PNG stores them all without discarding detail. Gradients and photos inside the screenshot add to it. Resize the screenshot or compress it, and share JPG only if there is no fine text.
Should I convert PNG to JPG to save space?
For photographs, yes, JPG is much smaller. For screenshots, logos and anything transparent, no: JPG is lossy, softens sharp text and has no transparency. Choose by content, and keep the PNG as a master. Fine text and thin lines are where compression shows first, so view the result at 100 percent before replacing anything.
Can I compress PNG files in bulk?
Yes. Select them all and run Compress › Compress. FileDial works in batches, saves new copies beside the originals and shows the size before and after on the result card. Compress under 500 KB and Compress to size… give a hard ceiling when a site or form limits uploads.