A Short Guide on Image Editing

Combined by Peter Berkesand

Contents

Introduction
Screen resolution
Scanning of images
Images from digital cameras
Image editing software
Some further links...


Introduction

In order for images to appear clearly in your scientific work images must be of high quality . This means that an image has to be of high resolution. There are three different ways of indicating image resolutions:

  1. ppi stands for pixel per inch and indicates the resolution in a screen
  2. dpi stands for dots per inch and and is used to indicate the resolution in a printer.
  3. lpi stands for lines per inch and is a way of describing the line density/frequency or resolution in for example a slide (diapositive)

Ppi and dpi are most frequently used but we employ the term ppi for screen resolution. One inch is equal to around 2.5 cm.

Go to the Top of the Page

Screen Resolution

An image that is ready to be printed should always be of 300 ppi or higher. The higher the ppi the better the resolution. Never use images with lower resolution and under no circumstances images from the Internet. Images on the Internet usually have a low resolution of around 72–75 ppi.
   Copying images, diagrams and tables from books, journas, magazins, newpapers and Internet without permisson from the copyright holder may violent copyright laws. Please take a look at our page on copyright.
   Please note! If you have a lot of high resolution images in your scientific work, the final pdf file will be very large. The file should not exceed three Megabyte and under no circumstances be more than 10 Megabyte. Should your file be larger than three Megabyte you may contact LiU-Tryck and ask them to reduce the images in the pdf file to a suitable size as they have special programs for that purpose. Should you need any other assistance with your images in your scientific work please do not hesitate to contact LiU-Tryck as they have both the expertise and equipment to help you produce a first-rate final scientific work.

Go to the Top of the Page

Scanning of Images

The software of a scanner determines more often than not the quality of the images. See to it that the original is of good quality. An original of poor quality will inevitably result in a poor image. When scanning on image make sure that the image is scanned to a larger size than the original itself. This is convenient in particular if the original image is small. This can however be adjusted in most scanner software. A large image may then be cut down/trimmed (downwards) to the preferred size. Images with too low resolution will be of very poor quality in print. The image will be pixelized (see figure 2 below). An image in printing quality should be of at least 300 ppi or higher. Please note! If you scan an image and save it in 72 ppi and then increase the resolution to 300 ppi it will end up pixelized. Always scan images in 300 ppi or higher.

Figure 1. An image should look like this in print. Photo: Peter Berkesand, Alsace, France, 2004.
Figure 2. A Pixelized image looks like this.

Go to the Top of the Page

Never scan images from newspapers or books as you then risk getting a moiré pattern in the image. Moiré is an interference that can be observed on the image when printed images are scanned. Simplified one could say that the pattern itself appears as if the image is printed on very thick cloth (see figure 3 below).


Figure 3. This is how an image with moiré pattern looks like.
Photo: Peter Berkesand, The chursh in Björkeberga, Sweden, 2004.


Scanning images from newspapers and books may also violate copyright laws. You may ask in writing for permission to use an image diagram or table from an article, book or brochure by using the form Permission Request.
   Save the scanned images in one of the following formats, TIFF, EPS, PSD (Photoshop) or AI (Illustrator). Never save the images in gif- or jpeg format as information may be lost as this type of file format is compressed.

Go to the Top of the Page

Images from Digital Cameras

Digital cameras have become both cheaper and of better quality through the years and images taken with digital cameras are therefore more frequently used. One should however note whether the camera is able to process high image resolutions. The table below shows the maximum image sizes that can be obtained from different camera resolutions.

Total Resolution
in Megapixel
Width x height
in pixels
Measure in cm of
images in 300 ppi
1 1280 x 960 10,84 x 8,13
2 1600 x 1200 13,55 x 10
3 2050 x 1900 17,34 x 13
4 2250 x 1700 19 x 14
5 2250 x 1900 21 x 16
6 3000 x 2000 23 x 18
8 3500 x 2000 27 x 20
10 3900 x 2600 30 x 23
12 4350 x 2900 36 x 24
16 4929 x 3264 41 x 27

Do not forget to save the image in TIFF-, EPS- or in Photoshop-format and high resolution in order to obtain the best possible quality. Then use image editing software in order to process and optimize the images with respect to size , sharpness/focus etc.

Go to the Top of the Page

Image Editing Software

There are several different software programs for image editing . Some of them are very expensive and others free. The best and most professional one on the market is Adobe Photoshop. This program is very expensive but there are cheaper alternatives. Adobe has launched Photoshop Elements which is a simpler version of Photoshop. It is available as a demo version and can be downloaded and tested. With this program you will manage to get quite far and it costs slightly more than one thousand SEK. GIMP is an excellent alternative to Photoshop. It was originally constructed for the platform Linux but is now available for Windows and furthermore it is for free. Yet another alternative is Paint Shop Pro. This program can be downloaded and tested for 30 days. The cost of this program is also around one thousand SEK. XnView is also a well worth alternative and has the most elementary needs. It is available for all platforms and is for free.
   Observe that you have to adjust the image resolution in the image editing software. Follow the instructions in the software manual. This is most often done under the command image size.

Go to the Top of the Page

Some Further Links…

...How to scan: http://www.scantips.com/ (in English)
...About image processing: http://www.ekdahl.org/kurs/index.html (in Swedish)
...About Paint Shop Pro: here you will find a multitude op pages, log on to Google and search. Write ”Paint Shop Pro” (including the inverted comas).
...About Photoshop: http://www.algonet.se/~stefwest/pskol/tips.html (in Swedish) or http://www.good-tutorials.com/ (in English) just taking a few examples. Search on Google for more.

>