Ultimate Guide to Image File Formats

It's no secret that images play a crucial role in our digital lives. We interact with various image file formats daily. But do you truly understand the intricacies of these formats and how they differ? Let's deep dive into what each file format can and can’t do, shed light on what each one is for, and help you decide the best one for your needs.

This article covers:

• Different image file types

• Pixel depth 

• The difference between RGB and CMYK colour models

• Help to decide what file format to choose

What are the different image file types? 

Before choosing an image file format, it's helpful to understand the different types of image files and their capabilities:

Raster Images

Raster images comprise a fixed number of pixels arranged in a grid pattern. Each pixel represents a single colour value. When there are enough pixels, they can form a coherent image that the human eye can see as a picture or object. The resolution of a raster image is determined by its number of pixels. Higher resolutions result in more detailed and sharper images, while lower resolutions can lead to pixelation or jagged edges.

Raster image files include JPEG, HEIF, GIF, PNG, TIFF, RAW, WEBP and PSD.

Vector image files

Vector images are a type of digital image defined by mathematical equations and geometric shapes rather than a grid of pixels like a raster image. They are ideal for resizing as they use line art equations to calculate and automatically adjust image proportions. This allows scaling without affecting file size or clarity. You can't create a vector image file using a camera.

Vector image files include PDF, EPS, SVG and AI.

What is Pixel Depth? 

Pixel depth, or bit depth, refers to the amount of data/information stored per pixel. You can measure pixel depth as bits per pixel (bpp). Typical pixel depths include 1 bpp (black and white), 8 bpp (grayscale), 24 bpp (true colour), and 32 bpp (true colour with transparency). Essentially, the higher the pixel depth, the better the colours look. 

24-bit images use 8 bits per RGB colour channel, providing 16.7 million possible colours. This extensive colour palette allows for highly detailed, nuanced, and realistic-looking images. In contrast, lower bit depths like 8-bit, which can only represent up to 256 colours, result in more limited and less precise colour reproduction. The higher the bit depth, the smoother the gradients and the more subtle the transitions between different hues and shades within the image. 

If you are curious about bit depth in the video world, then check out the difference between 8-bit and 10-bit in videography.

Image File Formats

By understanding these formats, their developers, and release years, you can make informed choices and ensure that your images are displayed and shared in the best possible way, whether you're a professional photographer, a web developer or a graphic designer. 

RAW: Capturing & Editing 

RAW files are unprocessed sensor data captured directly from a digital camera's image sensor. They typically have a colour depth of 12 or 14 bits per channel (36 or 42 bits per pixel).

Developed by: Various, each with their proprietary RAW formats. For example, DNG was developed by Adobe, Canon and Nikon developed CR2 and NEF in the 1990s.

Pros: Maximum image data, unparalleled flexibility for post-processing and editing

Cons: Large file sizes, require specific software for viewing and editing

Used for: Professional photography, post-processing and editing

JPEG: Versatility, Space & Web Publishing

JPEG uses lossy compression and supports 8 bits per channel (24 bits per pixel) for colour images. JPEGs are the most widely used image format. 

Developed by: The Joint Photographic Experts Group, released in 1992.

Pros: Balanced image quality and file size, widely supported

Cons: Lossy compression can degrade image quality, especially at high compression levels

Used for: Sharing and displaying images on the web, digital photography, general image use

PNG: Graphics & Transparent Backgrounds

PNG (Portable Network Graphics) is a lossless format that supports transparent alpha channels and 8 or 16 bits per channel (24 or 48 bits per pixel) for colour images, and up to 64 bits per pixel for true colour and grayscale images.

Developed by PNG Development Group, it was released in 1996 to replace the GIF format.

Pros: Lossless compression, supports transparency

Cons: Larger file sizes for photographic images

Used for: Graphics, logos, images with text or simple colours

GIF: Looping Animations

GIFs (Graphics Interchange Format) contain multiple images or frames that play in a loop, creating an animation. GIFs support a maximum of 8 bits per pixel, allowing a limited palette of up to 256 colours. 

Developed by CompuServe, released in 1987. 

Pros: Supports animation and transparency

Cons: Limited colour palette, unsuitable for high-quality photographic images

Used for: Simple graphics, icons, animated images on the web

TIFF: Better Quality & Printing

TIFF (Tagged Image File Format) can support various colour depths, including 8, 16, 32, and 64 bits per channel, depending on the compression method used.

Developed by Aldus—now the much more well-known Adobe—and Microsoft, introduced in the late 1980s.

Pros: Flexible, supports lossless and lossy compression, widely used in professional workflows

Cons: Can result in large file sizes, not widely supported on the web

Used for: High-quality photographic images, scanned documents, professional graphics, publishing, and prepress workflows

HEIF: High Efficiency & Quality

HEIF (High Efficiency Image Format) supports 8, 10, or 12 bits per channel (24, 30, or 36 bits per pixel) for colour images, as well as transparency and high dynamic range (HDR).

Developed by The Moving Picture Experts Group (MPEG), it was released in 2015 as a successor to JPEG.

Pros: Efficient compression, smaller file sizes than JPEG with better quality, supports advanced features

Cons: Limited support on older devices and software

Used for: Space-saving alternative to JPEG, especially on newer devices like smartphones

Note: While HEIF is a container format that can handle various media types, HEIC is the particular variant or instance of HEIF dedicated to still image files.

WebP: Space Saver

WebP is Google’s proprietary image format, designed for the web. WebP supports 8 bits per channel (24 bits per pixel) for lossy images and up to 14 bits per channel (42 bits per pixel) for lossless images.

Developed by: Google, released in 2010.

Pros: Superior compression, smaller file sizes than JPEG and PNG with comparable or better quality

Cons: Limited support on older browsers and devices

Used for: Web optimization, reducing page load times, sharing images on the web

As you can see, each image file format has its strengths, weaknesses, and unique characteristics tailored to specific use cases. 

Want to know how to edit these files? Read our guide to photo editing for beginners.

What’s the difference between RGB and CMYK colour modes?

RGB is an additive colour mode in which the primary colours red, green and blue are combined to create other colours. It is the standard colour mode for digital devices like monitors, cameras, and the web. Combining all three primaries at full intensity produces white. 

CMYK is a subtractive colour mode used in printing. The primary colours cyan, magenta, yellow and black are combined to create other colours by absorbing specific wavelengths of light. Combining all four primaries produces a rich black colour.

RGB has a wider colour gamut and is optimal for web and digital graphics, while CMYK is designed for print media and has a more limited colour range than RGB.

FAQs: What Image File Format Should I Choose?

The right image file format is crucial for optimal display, shareability, and print quality. Let's dive into the best formats for different use cases.

Which Image File Format is the Best Format to Use for Photographs on the Web? 

For web images, you'll want formats that balance quality and file size for fast loading across devices. JPEG is perfect for photographs, offering compressed yet high-quality visuals. PNG excels for graphics, logos, and images with transparency, supporting millions of colours. GIFs are ideal for simple animations and icons.

Which Web Format Allows For Millions of Colours and True Alpha Transparency?

PNG is the web image format that allows for millions of colours and true alpha transparency. While PNG offers excellent colour and transparency support, its lossless compression can result in larger file sizes compared to lossy formats like JPEG, especially for photographic images. 

What is the Best Image File Format for Sharing Images Online?

The trusty JPEG format is hard to beat for sharing photos via the web or social media. Modern smartphones often use HEIC (easily convertible to JPEG). PDFs are perfect for sharing multiple high-quality images at once.

What is the Best Image Format for Printing?

High-resolution JPEGs, PDFs and TIFFs are the best bets for printed materials like photos and documents. Adjust resolutions as needed for optimal print dimensions. You will also want a minimum of 300 DPI for printing photos. 

How Do I Optimise Images for my Website? 

To ensure the highest image quality on your website, use consistent pixel dimensions and choose formats tailored to your needs—JPEG for photos, PNG for graphics and logos, GIF for animations. Optimise file sizes (ideally, each image will be less than 1MB), add alt-text for accessibility and include relevant keywords for SEO.

Which Image File Format Is the Best JPEG Alternative?

While PNG is a widely adopted standard for lossless image compression, HEIF is a newer format that uses modern compression techniques to provide superior compression efficiency and image quality.

PNG and HEIF are excellent alternatives to JPEG, offering lossless compression and transparency support. However, HEIF has the added advantage of smaller file sizes and support for advanced imaging features like HDR and depth maps.

It's worth noting that while HEIF is steadily gaining adoption, especially in Apple's ecosystem, PNG remains the more widely supported format across various platforms and applications, ensuring broader compatibility.

What is the Highest Quality Image Format Overall?

The highest quality image format overall is TIFF. It is commonly used in professional photography, publishing and printing workflows, where preserving image quality and colour accuracy is critical.

Which Image File Formats Support Lossless Compression?

Several image file formats support lossless compression, meaning the original image data is preserved without losing quality or introducing compression artefacts. The main image formats that offer lossless compression are PNG, TIFF, WEBP, HEIF and JPEG 2000. 

Having trouble with your exposure? Read our handy guide to the exposure triangle, covering aperture, ISO and shutter speed. Or read more tips and techniques on the MPB content hub.