You export an image from your design tool and it asks you: JPEG, PNG, or WebP? You pick one, the image looks fine, and you move on. But behind that choice is a real tradeoff between file size, quality, and capability. Pick wrong and you can end up with images that are ten times larger than they need to be, or images that lose detail you wanted to keep.
Here’s what each format actually does and when to use it.
How Image Compression Works (the Short Version)
All image formats store pixel data, but they compress it differently. There are two fundamental approaches:
Lossy compression permanently removes some image data to achieve smaller files. You can’t get the original data back. The algorithm decides which details human eyes are least likely to notice and discards them. At low compression, the loss is invisible. At high compression, you get visible artifacts: blocky areas, color banding, blurred edges.
Lossless compression reduces file size without discarding any data. The original image can be perfectly reconstructed from the compressed file. The tradeoff is that lossless files are larger than lossy files of the same image.
JPEG: The Default for Photos
JPEG (Joint Photographic Experts Group) uses lossy compression. It was designed in 1992 specifically for photographic images and it remains the best choice for most photos.
How it works: JPEG breaks the image into 8×8 pixel blocks and applies a mathematical transformation (discrete cosine transform) to each block. It then quantizes the results, rounding off small differences that the human eye won’t notice. Higher compression means more aggressive rounding and more detail lost.
Where JPEG shines:
- Photographs and realistic images with smooth gradients and complex color
- Any image where a small amount of quality loss is acceptable
- When file size matters (web pages, email, social media)
Where JPEG fails:
- Images with sharp edges, text, or line art (the block-based compression creates visible artifacts around hard edges)
- Images that need transparency (JPEG doesn’t support it at all)
- Images that will be edited and re-saved repeatedly, since each save cycle loses more quality (generation loss)
Quality settings: JPEG quality is usually set on a 0-100 scale. For web images, 75-85 is typically the sweet spot: visually indistinguishable from 100 at normal viewing sizes, but often 60-80% smaller in file size. Below 60, artifacts become noticeable on most images.
PNG: When Every Pixel Matters
PNG (Portable Network Graphics) uses lossless compression. Every pixel in the saved image is identical to the original. It was created in 1996 as a patent-free replacement for GIF.
How it works: PNG uses a prediction-and-compression approach (DEFLATE algorithm). It predicts each pixel value based on neighboring pixels, then compresses the differences. Regions of solid color or repeating patterns compress very efficiently. Complex, noisy regions don’t compress as well.
Where PNG shines:
- Screenshots, text, logos, icons, and any image with sharp edges and flat colors
- Images that need transparency (PNG supports full alpha channel transparency, so each pixel can be any level of transparent)
- Images that will be edited further (no generation loss)
- Any case where visual accuracy is non-negotiable
Where PNG falls short:
- Photographs, where a PNG can easily be 5-10× larger than a JPEG of comparable visual quality
- Any situation where file size is the priority
A common mistake: Exporting a photo as PNG “for quality.” Yes, PNG preserves every pixel, but for a photograph, the file will be enormous and the quality difference from a JPEG at 85 will be invisible to the human eye. Save photos as JPEG (or WebP). Save screenshots and graphics as PNG.
WebP: The Modern Compromise
WebP is a format developed by Google, released in 2010. It supports both lossy and lossless compression, plus transparency and animation, essentially combining the strengths of JPEG, PNG, and GIF into one format.
How it works: Lossy WebP uses a prediction-based approach derived from the VP8 video codec. It predicts blocks of pixels based on surrounding data, then encodes only the difference. Lossless WebP uses a different algorithm that includes techniques like backward reference (reusing previously decoded pixels) and color cache (a palette of recently used colors).
Where WebP shines:
- Web images of any kind (it typically produces files 25-35% smaller than JPEG at equivalent visual quality)
- Lossless WebP files are typically 26% smaller than PNG
- When you need transparency with smaller files than PNG
- Web pages where every kilobyte of page weight affects load time and data costs
Where WebP has limitations:
- Browser support is now excellent (all modern browsers support it), but some older software and image editors still don’t handle it well
- If you’re distributing images for print or for users to download and edit, JPEG or PNG remain more universally compatible
- Some social media platforms and email clients still don’t display WebP natively
Quick Decision Guide
Is it a photograph or realistic image? → Use JPEG at quality 80 for web, or WebP for even smaller files.
Does it have text, sharp lines, or flat colors (screenshot, logo, diagram)? → Use PNG, or lossless WebP if you’re optimizing for file size.
Does it need transparency? → Use PNG for maximum compatibility, or WebP for smaller files.
Is page load speed critical? → Use WebP with a JPEG fallback for older contexts.
Will the image be edited and re-exported multiple times? → Work in PNG (lossless), export the final version in whatever format suits distribution.
File Size Matters More Than You Think
A single unoptimized PNG photo on a web page might be 3-5 MB. The same image as a JPEG at quality 80 might be 200-400 KB. As a WebP, maybe 150-300 KB.
That difference matters because:
- Mobile users on slow connections wait seconds longer per oversized image. On 3G, 5 MB takes roughly 15 seconds to download.
- Data caps are real in much of the world. A page with 10 MB of unoptimized images costs real money for users on metered connections.
- Core Web Vitals (Google’s page experience metrics) are directly affected by image size. Largest Contentful Paint (LCP), one of the three core metrics, measures how quickly the largest visible element loads. If that element is a large image, format choice directly impacts your score.
- Hosting costs scale with bandwidth. If your site serves millions of page views, the difference between 200 KB and 3 MB per image translates to real infrastructure costs.
Convert and Compress Your Images
Try the Image Converter on ToolzHQ to switch between JPEG, PNG, and WebP, or use the Image Compressor to reduce file size while keeping visual quality high. All processing happens in your browser, so your images never leave your device.