How to Compress a PNG on Windows

To learn how to compress a PNG on Windows you need to understand what the built in tools can do and where they stop. The answer is simple: the Photos app can resize an image and save it as a JPEG, but it offers no compression slider that actually affects a PNG file. Knowing this saves you from hunting for a control that does not exist. Windows 10 and Windows 11 behave identically here, so stop looking for a difference between the two versions.

How to Compress PNG Windows 10

The Photos app on Windows 10 gives you two real levers: dimensions and format. Open the image, click the Edit button, then choose Resize. You get preset sizes like 2000 px or 1080 px, or you can type a custom width. Resizing cuts file size by the square of the pixel reduction. An image stored at 3000 pixels wide but displayed at 800 carries roughly fourteen times the pixel data anyone will see. Resize to the actual display width first. For a blog image that is about 1600 pixels on the long edge. For full screen use about 2560 pixels covers it. High density screens need roughly twice the display width, not the full camera sensor.

After resizing, save as JPEG. The Photos app shows a quality slider only when you export to JPEG, not when you save as PNG. That slider is your real compression control on Windows. For a photograph stored as PNG, switching to JPEG at quality 85 typically shrinks the file to one tenth the size with no visible loss at normal viewing distance. If the image has transparency you cannot use JPEG, because JPEG has no alpha channel. Converting a transparent PNG to JPEG flattens transparency onto a solid colour, usually white.

Windows Photos App Resize Image

Open the image in the Photos app. Click the Edit icon in the toolbar, then select Resize image. The panel shows preset dimensions and a custom option. Choose a preset or type your own width and height. The aspect ratio locks by default; click the chain icon to unlock it. The resized image saves as a copy, leaving the original untouched. This is the only size reduction Windows offers without third party software.

The Photos app has no palette reduction. That means it cannot cut a 32 bit truecolour image down to a 256 colour palette. Palette reduction is where the real savings live for screenshots, logos, charts and line art. A UI screenshot shrinks 70 to 85 per cent when rebuilt from an adaptive 256 colour palette. Lossless optimisation alone, which only re runs the compression algorithm harder, saves 5 to 15 per cent. The difference is not small. Windows simply lacks the tool. If you need palette reduction on Windows without installing anything you are out of luck. You need Photoshop, GIMP, pngquant or an online service.

Why Windows Cannot Squeeze a PNG Properly

PNG is always compressed and always lossless. There is no uncompressed PNG. The format uses two stages: a filtering step that predicts each pixel from its neighbours and stores the difference, then a DEFLATE step that compresses those differences. Flat colours and repeated patterns make the prediction correct, so the differences are mostly zero and zeros compress to almost nothing. Photographic sensor noise makes the prediction wrong nearly every time, giving small random differences that are close to incompressible. That is why a photo as PNG is roughly ten times the size of the same photo as JPEG at an invisible quality difference.

The Quality Slider Misconception

A quality slider for JPEG controls how much high frequency detail the encoder discards. PNG promises exact pixels, so it can never do that. The Photos app is correct not to offer a PNG quality slider. The slider you see in the JPEG export path simply does not apply to PNG output. If you read advice telling you to drag a slider to compress a PNG, that advice is about JPEG.

What Lossless Optimisation Actually Does

Lossless tools like optipng and zopflipng search harder for the best filter per row and re run DEFLATE at maximum effort. They also strip metadata chunks like tEXt, iTXt, eXIf and ICCP colour profiles. The decoded pixels are identical to the original. Typical saving is 5 to 15 per cent, sometimes zero on an already optimised file. A correct tool returns the original if the re encoding would make the file larger. Windows has no such tool built in.

Palette Reduction Is the Real Saving

Palette reduction rebuilds the image from an adaptive palette of 256, 128 or 64 colours chosen from the colours actually present. Two effects compound: each pixel needs 7 or 8 bits instead of 24 or 32, and thousands of near identical shades collapse into one entry, creating exactly the repetition DEFLATE feeds on. A logo or icon shrinks 60 to 80 per cent. A chart or diagram shrinks 70 to 80 per cent. The visible failure mode is banding in smooth gradients and a stair step fringe on semi transparent edges. A gentler colour count fixes the latter.

What to Do When Resize is Not Enough

If resizing the image does not get the file small enough, and you cannot install software, your options on Windows are limited to two. First, save as JPEG if the image has no transparency. Second, accept the current size. The Photos app cannot strip metadata, reduce the colour palette, or try harder DEFLATE settings. That is where the built in tools stop.

If the image is a photograph stored as PNG, honest advice is to change format. The best compress png on Windows method for a photo is to save it as JPEG instead. For graphics and screenshots, resize to the actual display width and keep the PNG. The file will still be larger than a palette reduced version, but it will be smaller than the original camera export.

File Size Outcomes by Action

PNG Compression Workflow and Precautions

Palette reduction cannot be undone. Keep the original and compress a copy. Compressing an already palette reduced file again gives a worse result than going to the low colour count once, because the second pass chooses from an already impoverished set. Lossless re compression is safe to repeat.

Images are typically 50 to 70 per cent of a web page total weight. The hero image is usually the most effective thing to shrink. Declaring width and height on an image prevents the layout shift measured by Cumulative Layout Shift. Print resolution is far higher than screen and exposes banding invisible on a monitor. Send print the untouched original.

The cheapest order to reduce file size is: strip metadata losslessly, then reduce the palette in steps, then reduce dimensions, then change format. Windows covers step three. For the other steps you need a dedicated tool.