Image file types for different jobs

Image types and graphics file types for different jobs

There are a number of different image file types for printing or websites that photographs, images and graphics can be saved in, including TIFF, JPG, PNG, GIF, PSD and EPS. Each image file format has different features and is suitable for saving different types of images for different purposes.

Depending on how your final image will be used – web or print – there will be different requirements in terms of size and resolution, colour mode and file type.

Print image requirements

To ensure that photographs and images are crisp and clear when printed, the images need to be of a high enough quality and large enough size.

Images and photographs which are to be printed will usually need to be 300dpi resolution and the correct document size (inches, cm or mm) to match the finished print size.

Colour images for printing will usually be in CMYK colour mode or greyscale. Spot colours may also be used.

Web image requirements

Web images and web graphics need to be optimised so that the file size is small and will load fast on a web page.

Web images are usually 72dpi resolution, and will be sized down to a specific image size in pixels (e.g. 600px by 300px @ 72dpi).

RGB colour mode is used for most full-colour web images.
Greyscale and indexed colour can also be used.

Full colour or greyscale images and photographs for use on web pages, are normally saved as JPG files.

Limited colour images and graphics (such as a simple logo or icon) are often saved as GIF or PNG files.

Some common image file types

Here is a list of many of the most common image file formats and what they are most often used for, with a little bit of information about each file type.

JPG

JPG files are used where the file size needs to be as small as possible. Useful for websites and social media, or on-screen presentations.

The JPG file format is used to save photographs and images with lots of colours and shading as web images.

JPG can be used to save files for printing, but images should not be repeatedly saved as JPG.

Most digital cameras save their files as JPG.
Professional digital cameras and semi-professional cameras can often save as TIFF or RAW file format which gives better image quality, but the file sizes are much larger than a JPG file.

JPG files are compressed with what is known as lossy compression, which means that it actually throws away some image detail to reduce the file size. Therefore you should not open, edit and re-save a JPG file multiple times, as each time you do this some more image information is lost. This causes smooth areas of the image to become blocky, and object edges will become jagged.

PNG

The PNG file format is used to save flat artwork such as logos and simple graphics for websites. It is best for vector graphics, but is not good for saving photographs.

GIF

The GIF file format is used for simple flat artwork with a limited number of colours. Typically GIF format is used for artwork with less than 32 colours and no gradients or shading. Something like a black and white logo would be ideal for saving as a GIF.

Simple animations and frame changes can be created as animated GIFs.

TIFF

TIFF is a standard high quality image format which can be opened by most image editing software. It is used in most desktop publishing software.

TIFF files can be uncompressed, or compressed with LZW compression. LZW compression is a lossless compression and does not affect the image quality, unlike the lossy compression of JPG.

PSD

PSD is the file format used by Photoshop. It is able to hold extra image information such as editable layers and masks, colour adjustments and effects.

PSD files can be opened by Photoshop and some other photo editing applications. PSD files can be used in some desktop publishing applications.

EPS

EPS files come in different variants:

EPS image files from Photoshop can save extra information such as paths or channels with the image information, or can save special image modes such as duotones.

EPS files from Illustrator can save scaleable vector art and text, and are closely related to the PDF file format.

Colour modes

CMYK

CMYK colour mode is used for full-colour images which are to be printed.

CMYK colour mode is made up from four colour channels: Cyan, Magenta, Yellow, Black. Each pixel in a channel can have a value between 0 and 255.
CMYK is used for print processes.
Adding together cyan, magenta and yellow inks will create a colour which is nearly black. Black ink is therefore added to give pure black.

RGB

RGB colour mode is used for full colour images which will be viewed on a screen, such as websites.

RGB colour mode is made up from three colour channels: Red, Green, Blue. Each pixel in a channel can have a value between 0 and 255.
RGB is used for screen and light-based displays.
Adding together red, green and blue light, will create white light.

Greyscale

Greyscale colour mode is used for black and white photographic images.

Greyscale colour modes consist of only one black channel, which can have 256 shades varying from white to black.