Principles of Image Compression: How to Reduce File Size Without Losing Quality
How to compress images without losing quality is a crucial concern for many website administrators, designers, and developers. This article explores the principles of lossless image compression and common optimization methods.
What is Lossless Compression?
Lossless compression is a technique that reduces file size without affecting image quality. It mainly optimizes storage by removing redundant data without altering the visual appearance of the image. Common lossless compression formats include PNG, lossless WebP, and GIF.
Core Techniques of Lossless Compression
Run-Length Encoding (RLE)
RLE is a fundamental compression algorithm that reduces data size by replacing consecutive repeating pixel values with a "pixel value + repetition count" format. For example, a pixel data sequence AAAAABBBCC can be encoded as 5A3B2C, thereby reducing storage space.
Huffman Coding
Huffman coding is a variable-length encoding technique that creates an optimal encoding scheme based on the frequency of pixel values. It uses shorter binary codes for frequently occurring data, thereby reducing the overall file size. The PNG image format employs this technique for storage optimization.
Lossless WebP and the DEFLATE Algorithm
WebP supports lossless compression and uses the DEFLATE algorithm (similar to PNG), which is based on LZ77 compression and combines Huffman coding to further reduce data redundancy.
How to Efficiently Perform Lossless Compression?
If you want to reduce image file sizes without affecting quality, consider the following methods:
Optimize PNG Images: Use tools such as PNGQuant, OptiPNG, and TinyPNG to optimize PNG images by removing unnecessary metadata and reducing color depth.
Convert to Lossless WebP: WebP often provides better compression than PNG. You can use the cwebp -lossless command to convert images.
Remove Unnecessary Metadata: Most images contain EXIF data (e.g., camera information, capture time). Use ImageMagick or exiftool to remove this metadata and reduce file size.
If you want your website's images to be smaller and load faster, try using PixelUlti for image compression. We provide the best lossless compression solutions!