A Comprehensive Guide to Image File Formats: PNG vs JPEG

Images are a critical part of the modern web, but with so many image formats to choose from it can get confusing. In this in-depth guide, we’ll cover the key differences between the most common image file formats – PNG, JPEG, WebP, TIFF, GIF and more.

Whether you’re a designer trying to pick the best format for your images or just looking to understand more about how image compression works, this guide has you covered. Let’s dive in!

PNG vs JPEG: The Crucial Differences

PNG and JPEG represent the two most widely used lossless and lossy image formats on the web. But when should you use each one? Here are the key factors to consider:

1. Transparency Support

One of PNG’s biggest advantages over JPEG is built-in transparency support. PNG allows for partial transparency, known as an alpha channel, so you can have transparent or semi-transparent pixels in an image. The alpha channel stores the opacity of each pixel.

JPEG does not support any transparency or an alpha channel. Every pixel in a JPEG must be fully opaque.

For any image with transparency like logos, icons or textures, PNG is the only choice that preserves this. JPEG simply can’t store transparent data.

2. Lossless vs Lossy Compression

PNG uses lossless compression. This means no quality or original image data is lost when the file is compressed. The tradeoff is that the compression ratios are fairly limited compared to lossy formats.

JPEG uses lossy compression algorithms that analyze images and selectively discard or merge data that is least noticeable to the human eye. This allows JPEG to achieve much higher compression ratios than lossless formats like PNG.

The downside is a loss of quality and introduction of compression artifacts, especially at lower quality settings. For archival purposes, PNG may be preferable to guarantee zero quality loss.

3. Bit Depth

Bit depth refers to the amount of color information that can be stored per pixel in an image.

PNG has up to 48-bit color depth per pixel (16-bits per channel), allowing over 281 trillion possible colors. This helps avoid color banding when editing images.

Baseline JPEG images are limited to 24-bit color depth (8-bits per channel), which equates to around 16.7 million colors. This meets the needs of most use cases.

Higher bit depth provides more editing flexibility and gradients, but comes at the cost of larger files.

Key Strengths of JPEG Format

While PNG has advantages like transparency and lossless compression, JPEG’s extreme compression capabilities give it a major edge in some applications:

  • Tiny File Sizes – JPEG can be compressed significantly more than lossless formats like PNG, especially for photos and complex images. The tradeoff is quality loss at high compression.
  • Web & Mobile Friendly – JPEGs compress so well they reduce bandwidth and load faster on websites. This makes them preferable for web graphics, photos and mobile uses where small file size trumps perfect quality.
  • Simpler Encoding – JPEG takes less processing power to encode than lossless formats. This makes it fast to generate and ideal for mobile cameras and real-time compression needs.
  • Wider Hardware Support – JPEG enjoys nearly universal hardware and software support. PNG has great software support but some older devices may lack full PNG rendering capabilities.

JPEG vs PNG Comparison Chart

Here is a quick comparison chart highlighting some of the key differences between JPEG and PNG:

Image FormatJPEGPNG
Bit Depth8-bits (24-bit color)Up to 48-bits per pixel
Color PaletteFull RGBIndexed color optional
Best Use CasesPhotos, web imagesLogos, icons, texturing

JPEG Format Details and Options

JPEG offers a few additional options and modes that are good to know about:

  • Baseline JPEG – This is the standard JPEG format that all JPEG viewers must support. Provides 24-bit color and optional chroma subsampling.
  • Progressive JPEG – Stores image data in multiple passes for incremental display as the file downloads. Useful for web images.
  • Lossless JPEG – A lossless version of JPEG exists but it sees minimal browser support and use compared to lossless PNG.
  • Chroma Subsampling – A color compression technique that selectively reduces color resolution while retaining full brightness resolution.
  • Quality Setting – Controls level of lossy compression. Values range from 0 – 100%. Higher is better quality. Useful to optimize for file size vs quality.

Understanding PNG File Format

Beyond basic lossless PNG images, some additional PNG features are worth mentioning:

  • Interlacing – Similar to progressive JPEGs, interlaced PNGs store multiple versions of the image for faster initial display.
  • Palette Indexing – Stores image using a color palette table with up to 256 colors. Drastically shrinks files but hurts quality.
  • Animation – APNG format allows storing simple animations as sequential PNG frames. Useful for simple animated images.
  • Truecolor vs Indexed – Truecolor PNGs store full RGB data per pixel. Indexed PNGs use a color palette table and have reduced quality.
  • Bit Depth – PNG bit depth can vary widely from 1 to 48-bits per pixel depending on needs. Higher means larger files.

When to Use PNG vs JPEG

So when should you use PNG versus JPEG? Here are some general guidelines:

  • JPEG – Best for photos, complex images and web graphics where small file size matters most. Avoid JPEG for images with text, logos and sharp edges.
  • PNG – Great for images with transparency, text, logos and illustrations. Retains perfect quality and supports transparency. Larger files than JPEG.
  • Convert JPEG to PNG – If you have an existing JPEG but need transparency, convert it to a PNG to add an alpha channel. This will increase file size.
  • Convert PNG to JPEG – If file size matters more than quality, convert PNGs to JPEGs to shrink file size substantially. Just be aware of potential quality loss.

Beyond JPEG and PNG – Exploring Other Image Formats

JPEG and PNG may be the most ubiquitous choices, but here’s an overview of some other image formats you may encounter:

  • GIF – Limited to a 256 color palette. Used mainly for simple logos, icons and animated clips. Being replaced by PNG and video formats.
  • TIFF – Very versatile lossless format. Stores images uncompressed or with lossless/lossy compression. Used for high quality archiving and scans.
  • HEIF – New format developed by Apple that uses highly optimized HEVC compression. Great compression ratios but lacks browswer/app support currently.
  • WebP – Developed by Google to improve on JPEG compression. Up to 30% smaller than JPEGs but still lacks wide adoption.
  • AVIF – Uses AV1 video codec to offer massive compression ratios. Promising new contender but needs wider support.
  • JPEG 2000 – Allows both lossy and lossless compression in JPEG 2000 format. Never gained much traction vs traditional JPEG.
  • JPEG XR – Designed to replace JPEG format with better compression. Adoption stalled due to extensive licensing fees.

Key Takeaways and Best Practices

To wrap up, here are some top tips to keep in mind when working with images:

  • Use PNG for any images requiring transparency like logos and icons. JPEG can’t store alpha channels.
  • JPEG is great for photos and web images where small files matter. Expect some quality loss at high compression.
  • Avoid excessive JPEG compression for images with text, logos and illustrations. The artifacts can degrade quality.
  • If converting PNG to JPEG, inspect the results closely. Some loss of quality is likely at reduced file sizes.
  • For archiving original images with zero quality loss, PNG or lossless TIFF are good choices.
  • Be mindful of JPEG and PNG compression settings when exporting images for the web. Balance file size with quality needs.

I hope this comprehensive guide gives you a better grasp of the most common image formats available.