How to Compress PNG Files: Reduce Size Without Losing Quality

Why PNG Files Are So Large

PNG (Portable Network Graphics) is a lossless image format -- it preserves every pixel exactly as created, with no compression artifacts. This makes PNG ideal for screenshots, graphics with text, logos, diagrams, and any image where sharp edges and exact color reproduction matter. But this fidelity comes at a cost: file size.

A single high-resolution PNG screenshot can easily reach 5-15 MB. A set of product photos saved as PNG might consume hundreds of megabytes. Website pages loaded with unoptimized PNGs take seconds to load instead of milliseconds, hurting both user experience and SEO rankings.

The good news is that PNG files almost always contain significant optimization potential. Most PNGs can be reduced by 30-80% without any visible quality loss using the right compression techniques. This guide covers every method, from quick online tools to advanced optimization strategies.

How PNG Compression Works

PNG uses a two-stage compression pipeline:

Stage 1: Filtering -- Before compression, PNG applies a predictive filter to each row of pixels. The filter predicts each pixel's value based on neighboring pixels and stores only the difference. For images with smooth gradients or repeating patterns, the differences are small numbers (often zeros), which compress extremely well.

There are five filter types (None, Sub, Up, Average, Paeth), and the optimal filter can differ for each row. Choosing the best filter strategy is one of the key optimization decisions.

Stage 2: DEFLATE compression -- The filtered data is compressed using DEFLATE (the same algorithm used in ZIP files). DEFLATE finds repeated byte patterns and replaces them with shorter references. The compression level (1-9) controls how hard the algorithm searches for patterns -- higher levels find more patterns but take longer.

Lossless vs Lossy PNG Compression

Lossless compression reduces file size without changing a single pixel. The decompressed image is bit-for-bit identical to the original. This is what standard PNG compression does, and optimized tools can squeeze more efficiency from the DEFLATE stage.

Lossy PNG compression selectively reduces the number of colors in the image (color quantization) before applying lossless compression. A 24-bit PNG with 16 million possible colors might be reduced to an 8-bit palette of 256 carefully chosen colors. If the original image uses relatively few colors (as most screenshots and graphics do), the visual difference is imperceptible -- but the file size drops dramatically.

Method 1: Compress PNGs Online

The fastest way to compress PNG files is with an online tool that requires no installation.

Using ConvertIntoMP4's PNG Compressor

Our PNG compressor processes files directly in your browser:

1. Upload your PNG -- Drag and drop one or multiple PNG files into the upload area
2. Choose compression level -- Select from preset options (Light, Medium, Strong) or set a custom target
3. Preview the result -- Compare the original and compressed versions side by side
4. Download -- Get your compressed PNG files individually or as a ZIP archive

The tool automatically selects the optimal compression strategy based on your image content. Graphics with few colors get aggressive palette reduction. Photos get optimized DEFLATE with smart filtering.

For JPEG images, our JPEG compressor uses different algorithms optimized for photographic content. And if you need to compress multiple image formats at once, our image compressor handles PNG, JPEG, WebP, and more in a single batch.

Method 2: Command-Line Tools

For developers, designers, and power users who need programmatic compression or integration into build pipelines, command-line tools offer the most control.

pngquant (Lossy)

pngquant is the gold standard for lossy PNG compression. It reduces 24/32-bit PNGs to 8-bit palettized PNGs using a median-cut color quantization algorithm with Floyd-Steinberg dithering.

# Basic compression (auto quality)
pngquant image.png --output compressed.png

# Set quality range (min-max)
pngquant --quality=65-80 image.png -o compressed.png

# Batch compress all PNGs in a directory
pngquant --quality=65-80 --ext=.png --force *.png

OptiPNG (Lossless)

OptiPNG recompresses PNGs using optimal filter and DEFLATE settings without changing any pixel data.

# Optimize with maximum compression
optipng -o7 image.png

# Batch optimize
optipng -o5 *.png

Zopfli/ZopfliPNG (Lossless, Maximum)

Google's Zopfli algorithm produces DEFLATE-compatible output that is 3-8% smaller than standard DEFLATE. The tradeoff is dramatically slower compression (100x slower), but decompression is standard speed.

zopflipng --iterations=15 input.png output.png

Combining Tools for Maximum Compression

The ultimate compression pipeline combines lossy color reduction with optimized lossless compression:

pngquant --quality=65-80 input.png -o temp.png
zopflipng temp.png output.png
rm temp.png

This two-step approach typically achieves 70-85% reduction for web graphics.

Method 3: Desktop Applications

Adobe Photoshop

1. Open your PNG file
2. Go to File > Export > Export As (or Save for Web for legacy)
3. Select PNG format
4. Uncheck Transparency if not needed (saves 25% of data)
5. Reduce the image dimensions if the original is larger than needed
6. Click Export

Photoshop's "Smaller File" preset applies moderate lossy compression. For maximum control, use the legacy "Save for Web" dialog which shows file size in real time as you adjust settings.

GIMP (Free)

1. Open your PNG file
2. If the image has many colors, use Image > Mode > Indexed to reduce the palette
3. Go to File > Export As and choose PNG
4. Set compression level to 9 (maximum lossless)
5. Uncheck "Save background color" and other unnecessary metadata
6. Click Export

Optimization Strategies by Image Type

Different types of PNG images respond differently to compression techniques. Using the right strategy for each type maximizes savings.

Reducing PNG Size Before Compression

Compression works on the data you give it. Reducing the data before compression amplifies the savings.

Remove Unnecessary Metadata

PNG files can contain chunks of metadata: text comments, creation software info, timestamps, color profiles, and even thumbnails. Stripping these saves a few KB per file, which adds up in bulk.

# Remove all non-essential chunks with pngstrip or exiftool
exiftool -all= image.png

Resize to Actual Display Dimensions

A 4000x3000 PNG displayed at 800x600 on a webpage contains 25x more pixel data than necessary. Resize before compressing:

Our image resize tool lets you set exact dimensions or scale by percentage while preserving transparency and color profiles. Resizing from 4000x3000 to 800x600 reduces the raw pixel count from 12 million to 480,000 -- a 96% reduction before any compression algorithm even runs.

Remove Alpha Channel If Unused

Many PNG files include an alpha (transparency) channel even when every pixel is fully opaque. The alpha channel adds approximately 25% to the file size. If your image does not need transparency, flatten it onto a solid background and save as RGB (24-bit) instead of RGBA (32-bit).

PNG Compression for Web Performance

Website performance depends heavily on image optimization. Google's Core Web Vitals explicitly measure how fast the largest visual element loads (Largest Contentful Paint), and unoptimized PNGs are a top offender.

Web Optimization Checklist

1. Resize to display dimensions -- Never serve a 2000px image in an 800px container
2. Compress with lossy quantization -- 256-color PNGs are sufficient for most UI elements
3. Consider modern formats -- WebP and AVIF offer 30-50% smaller files than optimized PNG for equivalent quality
4. Use responsive images -- Serve different sizes for different screen widths via srcset
5. Lazy load below-the-fold images -- Only load images when they scroll into view
6. Enable HTTP compression -- Gzip/Brotli on the server provides another 5-10% on PNG files

For a comprehensive deep dive on web image optimization, check out our guide on how to compress images without quality loss. If you are considering switching from PNG to a more efficient format for web delivery, our AVIF vs WebP vs JPEG XL comparison covers the modern alternatives.

Should You Switch from PNG to WebP or AVIF?

For web delivery, modern formats offer compelling advantages over PNG:

• WebP -- 26% smaller than PNG (lossless) with support in all modern browsers
• AVIF -- Up to 50% smaller than PNG with wider color gamut and HDR support
• JPEG XL -- Up to 35% smaller with progressive decoding (browser support still limited)

However, PNG remains the right choice when you need guaranteed compatibility (email, documents, legacy systems), transparency with maximum quality (WebP lossy transparency can show artifacts), or pixel-perfect reproduction for archival purposes.

Batch Processing Workflows

For Web Developers (Build Pipeline)

Integrate PNG compression into your build process:

# npm package: imagemin with imagemin-pngquant
npm install imagemin imagemin-pngquant --save-dev

For Designers (Asset Export)

When exporting assets from Figma, Sketch, or Adobe XD:

1. Export at 1x, 2x, and 3x resolutions
2. Run all exported PNGs through our PNG compressor in a single batch
3. The compressed files replace the originals with optimized versions

For Content Teams (CMS Uploads)

Before uploading images to your CMS (WordPress, Shopify, Squarespace):

1. Resize images to the maximum display width of your content area
2. Compress using our online tool
3. Upload the optimized files
4. Verify the images look correct on the published page

For related image workflow topics, explore our guide on batch processing files. And if you need to combine multiple compressed PNGs into a single document, our images to PDF tool assembles them while preserving quality.

Common Mistakes to Avoid

Using PNG for photographs -- PNG is designed for graphics, not photos. Converting photos from JPEG to PNG for "better quality" actually wastes space without improving visible quality. Keep photos as JPEG (or AVIF/WebP for web).

Over-compressing with too few colors -- While 256 colors works for most graphics, images with complex gradients (sunset skies, skin tones, blurred backgrounds) may show visible banding. Test before deploying.

Compressing already-compressed PNGs -- Running an already-optimized PNG through compression again wastes time and produces negligible savings. Check if the file has already been processed.

Ignoring image dimensions -- Compression cannot compensate for serving a 5000px image in a 500px container. Resize first, then compress.

Forgetting retina displays -- For web, export at 2x the display size for retina/HiDPI screens, then let the browser scale down. A 1600px image displayed at 800px CSS width looks sharp on retina while allowing the browser to optimize rendering.

PNG compression is one of the highest-impact optimizations you can make for web performance, email efficiency, and storage management. Whether you use our online PNG compressor, command-line tools, or build-pipeline integration, the techniques in this guide will dramatically reduce your PNG file sizes while preserving the visual quality that made you choose PNG in the first place.