Understanding Image File Formats

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If you’re a website or graphic designer, photographer or just create documents with your word-processor, you are going to come across a variety of different image file formats. Knowing which one to use will not only improve the quality, but also make it easier to update and modify your images in the future.

In this article we’ll take a look at the differences, benefits and disadvantages of some of the more common ones.

Compressed and Uncompressed Formats

Both compressed and uncompressed file formats have their advantages depending on the intended use and application.

Uncompressed Images

Uncompressed files save the file in the same way that they exist as the open file. This means that the size of the file on the disk is the same as the file in memory. They retain all the original image data when you save, so they are the best formats to use for editing.

Compressed Images

The data by stored in compressed images is saved using complex algorithms so that the resulting file size is much smaller than an uncompressed image. Compressed image file formats are best used for the final output, but not recommended for editing due to the loss of data every time you save. There are two types of image compression: lossless and lossy compression.

Lossless Compression

The algorithm used in lossless compression loads the image into memory in its original state before compression.

Lossy Compression

The lossy compression algorithm discards data that is not essential to display the image. Files saved using lossy compression are great because the file size of images is much smaller and take up less space. However if the images need editing, you will lose a bit more data every time you save.

To get around this, you can use an uncompressed file format while editing and then save as a lossy format when you’re done. Always keep a copy of the original in case the image needs editing in the future.

Vector Images

The data for a vector image is stored in a series of “paths” as opposed to a raster image, where the data is a set of pixels with each pixel representing a point of light in the image. Logos, icons and graphics will benefit by being saved in vector format.

Vector vs Raster image comparison. The difference between common file formats
Vector images retain their quality when enlarged. Raster images will pixelate when enlarged.

This article is primarily about raster images, so if you need information on vector images, please see my post on vector file formats.

Image file types

Understanding some of the image file formats can help you in choosing which type to use as they both have their respective advantages and disadvantages.

Joint Photographic Experts Group (*.JPG; *.JPEG)

JPEG files are named after the Joint Photographic Experts Group and are probably the most common file format. It is a compressed file format with good image quality and supports 16.8 million colours. Most cameras and phones use the JPEG format by default.

The JPEG file format is widely supported and can easily be used on web pages. Being a compressed file format, the file size is relatively small in comparison to formats like TIFF.

JPEG images use a lossy compression algorithm so it is best to convert the files to an uncompressed format like TIFF for editing and then convert back to JPEG after the changes have been made.

Tagged Image File Format (*.Tiff; *.TIF)

The tagged image file format (TIFF) is an uncompressed file format and retains most of the original image data.

The files are much larger than JPEG images and are best kept for editing and back-up. They are generally not supported by web browsers but can be converted to a format that is, like JPG or PNG .

Compuserve GIF (*.GIF)

The Compuserve Graphics Interchange format (GIF) has been used in website development since the early days of The World Wide Web. GIF files us an 8-bit palette which is limited to 256 colours. This makes the files very small which allows them to be easily transferred across the internet.

GIF files also support animation so they’re very useful for creating images for buttons, links and icons for web pages. The files are lossless, so data will not be lost when editing and saving files.

Portable Network Graphics (*.PNG)

The Portable Network Graphics (PNG) image file format was originally designed to replace the GIF format for use on the internet. The file format supports 16.7 million colours as opposed to the 256 colours supported by the GIF format. PNG files use a lossless compression algorithm.

PNG files support transparency so they can be used for graphics that need to be superimposed over other graphics or backgrounds.

Encapsulated Postscript (*.EPS; *.PS)

The Encapsulated Postscript file format (EPS) was developed by Adobe as a means to save images in a format compatible with postscript printers. This meant that they could be copied to a printer without needing to interact with any native applications. The EPS file format became a means to transfer documents between different programs in the printing industry.

The strength of the format is that I can contain both raster and vector images. The EPS format has been widely used in the printing industry as the files can be used in most desktop layout programs.

Images saved as EPS are very large, so it is not an efficient format to save photos for editing and is best used for saving vector artwork.

Portable Document Format (*.PDF)

The PDF file format was developed by Adobe to be a standard format for files containing both vector and raster images that could be read by many applications. It has been widely accepted as the standard file format across all operating systems.

Native File Formats

All photo editing and graphics software will have their own file formats. Some examples include Photoshop (PSD), Illustrator (AI), CorelDraw (CDR) and Corel Photo-Paint (CPT). Native file formats can generally only be opened and edited with the application they were created in. For this reason, it is not advisable to share or distribute files in their native format. Rather convert to a format that is compatible with and can be edited in other software. 

Colour Models

In addition to the many image file formats and types, you will come across different colour models. Some examples are RGB, CMYK, Hex, HSB and Lab. The colour formats have specific uses and it’s just as important to use the correct colour model as it is to choose the file type.

It’s important to know that there is difference in how CMYK and RGB colours appear on digital and in print applications. Choose CMYK if you’re be printing, and use RGB for digital screen displays. Read more in my post on the CMYK and RGB Colour Models.

Need help with image file formats?

We can covert images to just about any format you may require. Contact us for more information or visit our services page for more of about what we do.

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Cimeron Collins

Cimeron is an artist and designer with more than 25 years experience in the printing and publishing industries. He lives in Edenvale, South Africa with his wife Tamay.

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