photo_libraryThe Two Most Common Image Formats
PNG and JPG are the two most widely used image formats on the internet and in everyday computing. JPG (formally JPEG) was developed by the Joint Photographic Experts Group and standardized in 1992, designed primarily for compressing photographic images. PNG (Portable Network Graphics) arrived in 1996, created by the W3C as a patent-free replacement for GIF, with a focus on lossless compression and transparency support.
Despite both being raster image formats, they take fundamentally different approaches to storing pixel data. JPG sacrifices some image data to achieve smaller files, while PNG preserves every pixel exactly as stored. This core difference drives every practical decision about when to use each format. Choosing incorrectly can mean bloated web pages, artifacts on your logos, or unnecessarily large photo files eating up storage.
compressHow JPG Compression Works
JPG uses lossy compression based on the Discrete Cosine Transform (DCT). The process works in several stages:
- Color space conversion: The image is converted from RGB to YCbCr, separating brightness (luminance) from color information (chrominance). Human eyes are more sensitive to brightness changes, so chrominance data can be compressed more aggressively.
- Block division: The image is divided into 8x8 pixel blocks. Each block is processed independently through the DCT.
- Frequency analysis: The DCT converts spatial pixel data into frequency coefficients. High-frequency details (sharp edges, noise) are separated from low-frequency content (smooth gradients).
- Quantization: This is where data is actually lost. A quantization matrix divides the frequency coefficients, rounding the results. Higher compression means more aggressive rounding, which discards more detail.
- Entropy coding: The remaining coefficients are compressed losslessly using Huffman coding or arithmetic coding.
The quality slider in most image editors (typically 1-100) controls the quantization step. At quality 85-95, most photographs look virtually identical to the original. Below 70, artifacts become visible — blocky patterns especially around sharp edges and text.
JPG also comes in two rendering modes: baseline (loads top-to-bottom) and progressive (loads as a blurry full image that sharpens). Progressive JPGs are generally preferred for web use since they provide a faster perceived loading experience.
layersHow PNG Compression Works
PNG uses lossless compression based on the DEFLATE algorithm (the same algorithm used in ZIP files). Every single pixel is preserved exactly — nothing is discarded. The compression process involves two steps:
- Filtering: Before compression, PNG applies a prediction filter to each row of pixels. Instead of storing raw pixel values, it stores the difference between each pixel and a predicted value (based on neighboring pixels). This pre-processing step makes the data more compressible by reducing redundancy.
- DEFLATE compression: The filtered data is compressed using a combination of LZ77 and Huffman coding. This is purely lossless — the original data can be perfectly reconstructed.
PNG comes in several variants:
- PNG-8: Supports up to 256 colors with an indexed palette. Produces very small files for simple graphics like icons and logos with limited colors.
- PNG-24: Supports 16.7 million colors (24-bit RGB, 8 bits per channel). Ideal for complex images requiring lossless quality without transparency.
- PNG-32: Adds an 8-bit alpha channel to PNG-24 for full transparency support, enabling 256 levels of translucency per pixel. This is what most people mean when they say "PNG with transparency."
balancePNG vs JPG: Side-by-Side Comparison
| Feature | JPG | PNG |
|---|---|---|
| Compression Type | Lossy | Lossless |
| File Size (photo) | Small (~200KB for 1920x1080) | Large (~2MB+ for 1920x1080) |
| File Size (logo/icon) | Medium (~25KB, may have artifacts) | Small (~15KB for simple graphics) |
| Transparency | Not supported | Full alpha channel support |
| Animation | Not supported | APNG supported (limited) |
| Color Depth | 24-bit (16.7M colors) | Up to 48-bit (trillions of colors) |
| Editing Impact | Quality degrades on each re-save | No quality loss on re-save |
| Best For | Photos, backgrounds, social media | Logos, icons, screenshots, text graphics |
| Browser Support | Universal (100%) | Universal (100%) |
| Year Introduced | 1992 | 1996 |
photo_cameraWhen to Use JPG
JPG excels in scenarios where the image contains complex, continuous-tone photographic content:
- Photographs: Any camera photo — portraits, landscapes, product shots, event photos. JPG's DCT compression is specifically tuned for the smooth gradients and complex color transitions found in photographs.
- Large background images: Hero banners, full-width background sections on websites. A 1920x1080 background at JPG quality 85 might be 200KB versus 2MB+ as PNG — a 10x difference that directly impacts page load time.
- Social media uploads: Platforms like Instagram, Facebook, and Twitter re-compress uploaded images anyway. Starting with a well-optimized JPG gives you the best quality-to-size ratio after their re-encoding.
- Email attachments: When file size matters and the recipient might be on a slow connection or limited storage.
- Digital art with smooth gradients: Paintings, illustrations with complex color blending — anywhere transparency isn't needed.
Pro Tip: For web photos, JPG quality 80-85 offers the best balance. Below 80, artifacts become noticeable. Above 90, file size increases dramatically with minimal visible improvement. Always test a few quality levels on representative images to find the sweet spot for your content.
design_servicesWhen to Use PNG
PNG is the clear choice when pixel-perfect accuracy, sharp edges, or transparency matter:
- Logos and brand assets: Logos need crisp edges and often require transparent backgrounds to sit cleanly on different colored surfaces. JPG compression creates visible artifacts around the sharp text and lines in logos.
- Icons and UI elements: App icons, buttons, badges — anything with flat colors, sharp geometric shapes, and clean lines. PNG-8 often produces tiny files for these use cases.
- Screenshots: Screen captures of text, code, UI mockups, or software interfaces. Text rendered in JPG shows obvious compression halos around each character. PNG preserves text perfectly.
- Text-heavy images: Infographics, charts, diagrams, or any image containing readable text.
- Images requiring transparency: Product photos on transparent backgrounds, overlays, watermarks, UI sprites.
- Graphics with sharp edges: Line art, pixel art, architectural drawings, technical diagrams.
- Images that will be edited repeatedly: Since PNG is lossless, you can open, edit, and re-save without accumulating compression artifacts. JPG degrades with each save cycle.
data_usageReal-World File Size Comparisons
Understanding actual file sizes helps make practical decisions:
- 1920x1080 photograph: JPG at quality 85 ≈ 200KB | PNG ≈ 2-4MB. JPG is roughly 10-20x smaller. The quality difference is negligible to the human eye for photographic content.
- 500x500 logo (flat colors): PNG-8 ≈ 8-15KB | JPG at quality 90 ≈ 20-30KB with visible artifacts around edges. PNG is actually smaller AND higher quality for this use case.
- 1280x720 screenshot (text + UI): PNG ≈ 150-400KB | JPG at quality 90 ≈ 100-200KB but with blurry text halos. PNG is worth the extra size for readability.
- 800x600 simple chart: PNG-8 ≈ 20KB | PNG-24 ≈ 80KB | JPG ≈ 40KB with artifacts. PNG-8 wins on both size and quality.
Key Insight: PNG can actually be smaller than JPG for images with large areas of uniform color, few colors overall, or sharp geometric patterns. The common assumption that "JPG is always smaller" is wrong — it depends entirely on the image content.
swap_horizConverting Between PNG and JPG
Converting between formats is straightforward, but understand the trade-offs:
- PNG to JPG: Useful when you need to reduce file size for sharing or web upload, and transparency isn't required. The conversion applies lossy compression, so save at quality 85+ for best results. Any transparency will be replaced with a solid background color (usually white). FastlyConvert's PNG to JPG converter handles this automatically.
- JPG to PNG: Converts the image to lossless storage, but won't recover quality already lost during JPG compression. Useful when you need to add transparency, or when you want to prevent further quality degradation from re-saving. Use our JPG to PNG converter for instant conversion.
A word of caution: converting JPG → PNG → JPG is wasteful. The intermediate PNG step inflates the file size without adding quality, and the final JPG compression loses data again. Always work from your original source file when possible.
rocket_launchWhat About WebP?
If you're optimizing for the web specifically, WebP deserves consideration as a modern alternative to both PNG and JPG. Created by Google, WebP supports both lossy and lossless compression, transparency, and animation — effectively combining the strengths of JPG and PNG in one format. WebP lossy images are typically 25-34% smaller than equivalent JPGs, and WebP lossless images are 26% smaller than PNGs. With browser support now exceeding 97%, WebP is a compelling choice for web-first content. For a deeper dive, see our HEIC vs JPG vs WebP comparison guide.
checklistQuick Decision Guide
Use this quick checklist to choose the right format:
- Is it a photograph or has complex color gradients? → Use JPG
- Does it need a transparent background? → Use PNG
- Is it a logo, icon, or contains text? → Use PNG
- Will it be edited and re-saved multiple times? → Use PNG (or keep as PSD/TIFF)
- Is web performance the top priority? → Consider WebP (lossy for photos, lossless for graphics)
- Is it a screenshot or technical diagram? → Use PNG
- Sending a photo via email and need small file? → Use JPG at quality 80-85
Need to convert between PNG and JPG?
FastlyConvert makes format conversion instant — no software to install, no quality compromises.
sync_alt Convert PNG to JPG NowFrequently Asked Questions
Which format supports transparency, PNG or JPG?
PNG is the format to use for transparency. It includes an 'alpha channel' that allows each pixel to have varying levels of opacity, which is perfect for logos or images that need to be placed over different backgrounds. JPG does not support transparency.
I'm saving a screenshot with text. Should I use PNG or JPG?
Always use PNG for screenshots, especially those containing text or user interface elements. PNG's lossless compression keeps text and sharp lines perfectly crisp and readable, whereas JPG's lossy compression will create noticeable blurry artifacts around the text.
How do PNG and JPG affect website performance?
JPG is generally much better for web performance when it comes to photographs because the file sizes are significantly smaller, leading to faster page load times. However, for simple graphics like logos and icons, a well-optimized PNG-8 can actually be smaller than a JPG and will look much cleaner.
Is there a quality difference for printing?
For high-quality printing, you should ideally use a lossless format like TIFF or a high-quality PNG from the original source. If you must use JPG, save it at the highest possible quality setting (100) to minimize compression artifacts that could be visible in a high-resolution print.
What happens when I convert a JPG to a PNG?
Converting a JPG to a PNG will prevent any further quality loss from re-saving, but it will not restore the image quality that was already lost when the JPG was first created. The resulting PNG file will be significantly larger than the source JPG because it is now storing that compressed data in a lossless format.