PNG vs JPG: Complete Format Comparison

PNG (Portable Network Graphics) was developed in 1996 as a patent-free replacement for GIF. The format quickly became the standard for web graphics, icons, and any image requiring transparency or lossless quality. PNG's defining characteristic is its lossless compression, meaning every pixel of the original image is preserved exactly.

Unlike JPG which sacrifices some image data for smaller files, PNG compresses data without any loss. This makes PNG ideal for images where quality is paramount, such as logos, screenshots, graphics with text, and images that will be edited multiple times. The trade-off is larger file sizes compared to lossy formats.

Key Features of PNG

• Lossless Compression: No quality degradation no matter how many times you save
• Transparency Support: Full alpha channel for smooth, anti-aliased transparency
• High Color Depth: Supports up to 48-bit truecolor and 16-bit grayscale
• Sharp Edges: Perfect for text, logos, and graphics with hard lines
• Animation: APNG extension supports animation (better than GIF quality)
• Gamma Correction: Embedded gamma for consistent display across devices

PNG Compression Levels

PNG offers compression levels from 0 (no compression, fastest) to 9 (maximum compression, slowest). Unlike JPG quality settings, PNG compression levels only affect file size and processing time, never image quality. A PNG saved at compression level 1 and level 9 will look identical; the level 9 file will just be smaller and take longer to encode.

Transparency Comparison

PNG's transparency support is one of its most important features. PNG uses an alpha channel that allows for 256 levels of transparency (0-255) per pixel, enabling smooth anti-aliased edges that blend seamlessly with any background. JPG cannot store transparency; any transparent areas become a solid color (usually white or black) when saved as JPG.

Text and Sharp Edges

PNG excels at preserving sharp edges and text. Because it uses lossless compression, every pixel remains exactly as designed. JPG's lossy compression can create "ringing" artifacts around sharp edges and text, where colors bleed slightly into surrounding areas. This is why screenshots and graphics with text should always be saved as PNG.

File Size Comparison Example

For a typical 12-megapixel photograph:

• Uncompressed BMP: ~36 MB
• PNG (maximum compression): ~18-25 MB
• JPG at 95% quality: ~4-6 MB
• JPG at 80% quality: ~1.5-2.5 MB
• JPG at 60% quality: ~0.8-1.2 MB

For a simple logo (500x500 pixels, flat colors):

• PNG: ~15-50 KB (efficient for flat colors)
• JPG at 90% quality: ~30-80 KB (may have artifacts)

PNG Compression (DEFLATE)

PNG uses the DEFLATE compression algorithm, the same lossless compression used in ZIP files. The compression process involves two steps: filtering (preprocessing pixels to make them more compressible) and DEFLATE compression (finding repeated patterns).

PNG's filters analyze each row of pixels and encode differences rather than absolute values. For images with gradual color changes, this creates highly compressible data. For random or noisy data (like photographs), the filters are less effective, which is why PNG files of photos are so large.

JPG Compression (DCT)

JPG uses Discrete Cosine Transform (DCT), a mathematical technique that converts image data into frequency components. The image is divided into 8x8 pixel blocks, and each block is transformed into a matrix of frequency values.

High-frequency components (fine details) are then quantized more aggressively than low-frequency components (overall shapes and colors). This exploits human perception: we notice changes in brightness and large shapes more than fine texture details. The quantization step is where quality loss occurs, but it enables dramatic file size reduction.

Why PNG is Better for Graphics

Graphics with flat colors, sharp edges, and text have very different compression characteristics than photographs. PNG's filters excel at encoding long runs of identical colors and gradual transitions. JPG's 8x8 block structure can create visible artifacts on sharp edges and text.

Additionally, PNG-8 (8-bit color with palette) can produce extremely small files for simple graphics with 256 or fewer colors, often smaller than an equivalent JPG file.