Understanding the Two Most Popular Image Formats
JPG (also known as JPEG) and PNG are the two most widely used image formats on the internet, together accounting for over 70% of all images served on the web. Despite both being raster image formats, they use fundamentally different compression strategies and excel in entirely different scenarios.
Choosing the wrong format is one of the most common mistakes in image optimization. A photograph saved as PNG can be 5–10× larger than the same image saved as a properly compressed JPG. Conversely, a logo or screenshot saved as JPG often looks noticeably worse than the PNG version due to compression artifacts around sharp edges.
This guide breaks down every meaningful difference so you can make the right choice every time.
Compression Methods: Lossy vs Lossless
JPG uses lossy compression. When you save an image as JPG, the algorithm permanently discards some visual information to achieve smaller file sizes. The amount discarded depends on the quality setting — higher quality retains more detail but produces larger files. Crucially, every time you re-save a JPG, additional quality is lost. This is called generational loss.
PNG uses lossless compression. The compression algorithm finds patterns and redundancies in the pixel data and encodes them more efficiently, but no information is ever discarded. You can open, edit, and re-save a PNG thousands of times with zero quality degradation. The decompressed image is bit-for-bit identical to the original.
This fundamental difference drives every other comparison between the two formats.
File Size Comparison
For photographs and images with complex color gradients, JPG is dramatically more efficient:
- A typical 1920×1080 photograph: JPG at 80% quality ≈ 200–400KB; PNG ≈ 2–5MB
- A 4K photograph: JPG at 80% ≈ 800KB–1.5MB; PNG ≈ 8–15MB
- JPG is typically 5–10× smaller than PNG for photographic content
For graphics, logos, and screenshots with large areas of solid color, PNG is competitive or even smaller:
- A simple logo (500×200): PNG ≈ 5–20KB; JPG at 90% ≈ 15–40KB
- A screenshot with text: PNG ≈ 100–300KB; JPG at 80% ≈ 80–200KB (but with visible artifacts)
- An icon or button graphic: PNG ≈ 1–10KB; JPG ≈ 5–15KB
The takeaway: JPG wins overwhelmingly on file size for photos; PNG is efficient for flat-color graphics.
Quality Characteristics
JPG artifacts are most visible around sharp edges, text, and areas of high contrast. You may notice:
- Mosquito noise — halos or ringing around sharp edges
- Blocking — visible 8×8 pixel grid patterns in smooth gradients
- Color bleeding — colors smearing across sharp boundaries
- Banding — smooth gradients turning into visible steps
PNG preserves every pixel perfectly. Text remains razor-sharp, edges stay crisp, and solid colors remain uniform. There are no artifacts of any kind because no data is lost.
For this reason, screenshots containing text, UI elements, code, or diagrams should almost always be saved as PNG.
Transparency Support
JPG does not support transparency. Every pixel must have a solid color. If you have an image with a transparent background (such as a logo), saving it as JPG will fill the transparent areas with a solid color — usually white or black.
PNG supports full alpha transparency. Each pixel can have 256 levels of transparency, from fully opaque to fully transparent. This makes PNG essential for logos, icons, overlays, watermarks, and any graphic that needs to be placed on varying backgrounds.
If your image requires any transparency, PNG is your only choice between these two formats (WebP also supports transparency and is worth considering).
Color Depth
JPG supports 24-bit color (16.7 million colors) using the YCbCr color model. This is more than sufficient for photographs and most visual content.
PNG supports multiple color modes:
- PNG-8 — 256 colors with optional transparency (palette-based, very small files)
- PNG-24 — 16.7 million colors (true color, no transparency)
- PNG-32 — 16.7 million colors plus full alpha transparency (the most common PNG variant on the web)
- PNG-48 — 48-bit color for professional/scientific imaging
For most web use cases, 24-bit color (available in both formats) is sufficient. PNG-8 is an excellent choice for simple graphics where 256 colors are enough, as it produces very small files.
Use Case Decision Guide
Use this decision flowchart to choose the right format:
- Does the image need transparency? → Yes → PNG
- Is it a photograph or complex image with many colors? → Yes → JPG
- Does it contain text, sharp edges, or screenshots? → Yes → PNG
- Is it a logo, icon, or graphic with flat colors? → Yes → PNG (or SVG)
- Will it be edited and re-saved multiple times? → Yes → PNG (to avoid generational loss)
- Is file size the top priority for a photo? → Yes → JPG
- Is it for social media or email? → Photos → JPG; Graphics → PNG
Web Performance Implications
On the web, image format choice directly impacts Core Web Vitals and page load speed. Using the wrong format wastes bandwidth and slows down your site:
- Serving photos as PNG instead of JPG can increase page weight by 3–5× unnecessarily
- Serving text-heavy screenshots as JPG makes them look blurry and unprofessional
- Google PageSpeed Insights specifically flags images served in non-optimal formats
For maximum web performance, consider using WebP as a modern alternative that combines the best of both worlds — lossy compression rivaling JPG for photos and lossless compression matching PNG for graphics, all at smaller file sizes. Use HeyCompress to convert and compress images to the optimal format quickly.
Best Practices Summary
- Use JPG for all photographs, natural images, and complex imagery at 75–85% quality
- Use PNG for logos, icons, text-heavy images, screenshots, and anything needing transparency
- Consider PNG-8 for simple graphics to get much smaller files than PNG-24/32
- Never repeatedly edit and re-save JPG files — keep a PNG or TIFF master copy
- When possible, offer WebP as a modern alternative with appropriate fallbacks
- Always resize images to their display dimensions before applying compression
- Use tools like HeyCompress that automatically optimize for the selected format