In this first instalment of Studentlitteraturs's image school, we take a closer look at issues of image format and technical quality. In part 2, we look at the rights required to use an image. 

Images for print and web

Image material for a book or educational material is often obtained form online image agencies where the poublisher, after agreeing on remuneration and are of use, can directly download the images electronically in the desired size. This ensures that you get images that are suitable for publication both in print and online. 
If you have taken an image that you wold like to include in your book, or perhaps found an image online, it is good to know a little about the technical requirements for an image to be used in print. Here are some rules of thumb. 

Image resolution

A digital photographic iamge is made up of a grid of samll square colour squares -pixels. A standard digital camera can produce images made up of millions of pixels; 4-10 megapixels(millions of pixels) is not uncommon. 

If the image is not to be printed with good quality in a book, 120 usch pixels are needed per centimetre of image. We often talk about images having a resolution of 300 dpi (dots per inch). This means 300 pixels per inch=120 pixels/cm

Check the size of the image

To check the number of pixels in an image, you can right-click on the file to get more information about it. Windows, select properties>information. This will give you the number of pixels in the image. In Mac, right-click on the dile and select view info.

How big will the image be when printed?
An example: The image is 960 pixels wide and 600 pixels high. This means that the printed image will be 8 centimetres wide(divide the pixels if the width by 120) and 5 cm high (divide the pixels of the height by 120)

Filformat

There are several common file formats for digital images. The tiff format is common and suitable format for saving images to be printed. Many digital cameras save images in jpeg format instead. To uese images for printing, the camera should be set to the lowest possible compression and highest npossible resolution. Avoid re-saving an image several times in jpeg as the quality of the pixels deteriorates each time. For images created in vector-based drawing programmes such as illustrator, the main format used is eps or ai. Read more about the different formats in the glossary below.

Images from the web

Images from the web often cause problems if they are to be used in print. An image that cover 1/4 of a normal monitor is enough for an image that is about 4 centimetres in print. This is because images on websites often have a resolution of only 72 dpi, a much lower resolution that that of a printed image (300dpi)
Ask the publisher for help. Sometimes the editor can find a similar image through one of the image agencies the publisher works with. 
And if the image is reproduced in an older printes work, for example, it is sometimes possible to scan the image from there and obtain a printable original. 

Feel free to contact the publisher

If you are woring on a manuscript and have questions about image quality, file forats or otyher issues related to the images, it is always a good idea to contact the pubisher. Your editor or educational material developer will be happy to help you. 

Short glossary


bitmap image made up of small squares. When enlarged, the whole image looks gridded. 
cmyk color system in image processing, where the letters stand for the colours cyan(blue), magenta(red) yellow and key colour (black), which are the four basic colours of printing technology. 
dpi dots per inch. A digital image is made up of dots (also called pixels) and the number of dots is expressed in dpi, the resolution of an image. 
eps encapsulated postscript, file format for digitised iamges, especially for vector garphics (see vector-based image)
gif graphic interchange format. An older standard for images intended for web publishing. 
jpeg (jpg) joint photographic expert group, a way of compressing digitised images so that they take up less space during storage or transmission. Avoid reaving an image sveral times in jpeg as the quality of the pixels deteriorates each time. Low-resolution images images that contain few pixels relative to tehir size, such as in a printed book. 
low-resolution images Images that contain few pixels relative to their size in, for ezample, a printed book. 
pixel points in a digitised image. 
png portable network graphics, a format for web images(not supported by older browsers) Developed partly as a replacement for the gif format. 
psd Photoshop´s own format for storing images. 
raster filter that divided a surface, such as a photograph, into small dots necessary for printing. Most easily seen when studying a printed image with a magnifying glass. 
rgb red, green, blue. The same colour mix as on the computer screen and television. 
tif, tiff tagged image file format, file format for digitised pizel images for PC and Mac respectively. Suitable image format for saving images to be printed. 
resolution number of dots (pixels) per inch of a digital image. 
vector-based image mathematically constructed image, can be enlarged without loss of quality.