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Portable Network Graphics — lossless image format with transparency. Ideal for screenshots, UI assets, and diagrams.
A group of developers created PNG (Portable Network Graphics) in 1996 as a patent-free replacement for GIF, after Unisys began enforcing the LZW compression patent that GIF relied upon. The W3C standardized PNG, and it has become the most widely used lossless image format on the web. PNG supports full-color (24-bit RGB and 32-bit RGBA) images with an alpha channel for transparency, making it the standard format for UI assets, icons, logos, diagrams, screenshots, and any image where visual fidelity must be preserved exactly. The format uses DEFLATE compression (the same algorithm as gzip) to reduce file size without any quality loss — every pixel is reproduced exactly as authored.
PNG supports interlacing for progressive loading, embedded color profiles (sRGB, ICC), gamma correction metadata, and text chunks for storing metadata like author and description. The format excels in images with flat colors, text, sharp edges, and transparency — areas where JPEG's lossy compression produces visible artifacts. Modern web development workflows generate PNGs for favicons, Open Graph images, app icons at multiple resolutions, and sprite sheets. Design tools like Figma, Sketch, and Adobe XD export components as PNG for handoff to developers.
Automated visual regression testing frameworks (Percy, Chromatic, Playwright) capture and compare screenshots as PNG files, making PNG comparison essential to modern CI/CD quality assurance. While WebP and AVIF offer better compression ratios, PNG's universal support, lossless guarantee, and transparency capabilities keep it indispensable for precision-critical visual assets.
PNG comparison uses pixel-level overlay to reveal visual differences that are invisible to the human eye in casual inspection. Comparing PNG files catches subtle anti-aliasing changes in UI components, shifted elements that are off by a single pixel, transparency channel modifications that affect compositing, and color profile changes that alter rendering across displays.
Design teams reviewing asset updates and QA engineers running visual regression tests depend on pixel-accurate PNG comparison to verify that only intended changes were made.
UtraDiff compares PNG images using four visual diff modes: pixel overlay highlights every changed pixel in a contrasting color, heatmap shows change intensity with a gradient from subtle to severe, onion skin crossfades between versions with an adjustable opacity slider, and side-by-side renders both images at matched scale for direct visual inspection. Metadata differences — resolution, color depth, and embedded ICC profiles — are reported alongside the visual comparison for complete change coverage.
Supported extensions: .png