File Types

When to use eps and jpg files, what’s the difference between Adobe Photoshop and Adobe Illustrator?

Image files can be broken down into two basic families – Raster or Bitmap images which include .jpg, .gif, .tif, .png and Vector images such as .eps, .svg and .ai.

Adobe Photoshop and other paint programs use Raster or Bitmap files and are pixel based. In effect each image is made up of small coloured squares (pixels). These images look ‘jaggy’ when enlarged and best suited to photographs. Pixel based images tend to be much larger files than Vector files as they contain far more information. Find out more about Adobe Photoshop from the Adobe website.

Vector images are used by programs like Adobe Illustrator. They use descriptive points connected by lines to form shapes. These files can be enlarged to any size without any loss of quality. Your logo should be produced as a Vector graphic. Find out more about Adobe Illustrator from the Adobe website.

Raster vs Vector Image size comparison: So, as an example, to draw the square below, a Raster file would need to code 36 pixels (squares). The bigger the square the more pixels would need to be added. The Vector square on the other hand would only need four points to construct the same square, whatever size it was.

Comparing raster to bitmap images graphic

Raster vs Vector Image quality comparison: You won’t be able to tell the difference quality wise between the two file types so easily with a square. But as soon as you bring in a curve the difference in quality becomes obvious:

Drawing curves - raster vs bitmap

The Raster image has to use square pixels to make up the curve while the Vector simply draws a line between two points (in this instance a curve is specified) resulting in a smooth curve whatever the size.

A note on Acrobat pdf files – Vector files are quite often saved as pdf files as they are more convenient and easier to use. But they can also contain Raster images. Just saving a Raster image to a pdf doesn’t make it a Vector pdf.

So is your .jpg file big enough to print from?
For an A4 full page image (210mm x 297mm) your file will need to be around 2480 x 3500 pixels. The file size will be in the region of 4mb.
For an A5 page image (148.5mm x 210mm) your file will need to be around 1755 x 2490 pixels. The file size will be in the region of 2.8mb.
For a landscape image going into single column on a two column grid A4 size (80mm x 70mm) your file will need to be around 945 x 830 pixels and 600kb in size.

Obviously if you are only using a portion of the photo the file size would need to be larger.

You can find the file size by selecting and pressing Command + I on a Mac or Alt + Enter on a Windows computer).

View more Graphic Design tips:

Graphic Design – So what is it?

File Types – Know the difference between jpg and eps and when to use them.

Artwork Basics – RGB vs CMYK, bleed and trims.

Typography – The forgotten art? Kerning and quotations

Magazine Design Basics – Design tips for producing a magazine, leaflet or brochure.

The Eyes Have It – Leading the eye in graphic design