An increasing problem we have noticed in recent years; with the introduction of affordable digital cameras and the use of the internet for a readily available supply of photographs, is the decline in the quality of images. Therefore we have produced this simple guide to assist when preparing images for reproduction.
The majority of the pictures that pass through the prepress department are of a very high quality, but every now and again we receive either a photograph or a logo that is of an insufficient resolution. Most of the work we print is at a screen ruling of 150 line per inch (lpi), and as a general rule of thumb continuous tone images, ie photographs, should have a resolution; dots per inch (dpi), of twice the lpi – 300dpi, when the image is at the correct reproduction size; we have produced acceptable images at 200dpi, but with lower resolutions the image reproduction quality will suffer. For bitmaps, such as logos, the resolution should ideally be much higher; at least 600dpi, preferably 1200dpi where text is incuded in the bitmap.
As a rough guide when using a digital camera to produce a suitable image for printing at 300dpi:
- a 3.0m pixel camera will produce an image 17 x 13cm,
- a 5.0m pixel camera will produce an image 21 x 16cm
- an 8.0m pixel camera will produce an image 27 x 20cm.