Home page > Digital data > Digital images > Introduction

Digital images

For much humanities research, images are important source material. This includes old photographs, images of paintings, sculptures, modern design objects, as well as images of archaeological artefacts and scans of historical documents, posters and newspapers. Just as text files, these types of images are being made digitally available to an increasing extent, but researchers might sometimes have to digitise them themselves. Digitised images can play the following roles in humanities research:

• analog objects that are not or not easily accessible for research purposes can easily be made available as digital images via the internet;
• research projects in which multiple objects are studied and compared (which may be spread across multiple locations all over the world) become easier and more financially feasible to conduct;
• digitised images can be processed by various types of computer-assisted image analysis;
• digitised images play an important role in scientific publications about the objects in question.

Apart from these advantages, however, as stated in the article Advantages and disadvantages in viewing today's high-resolution images of artworks on the Essential Vermeer website, "viewing digital images of artworks present important lacunae in respect to the original art works they represent. Digital images are formed by adjacent pixels which emit different frequencies of light. However, paintings are three-dimensional physical objects made of successive layers of variegated substances which combine in unique and unusual manners. Obviously, even in the best of case, a painting's dimensions and texture, both absolutely crucial components of a serious viewing experience, are in lost to a significant extent in even the best digital image."

For academic purposes, digital reproductions must meet minimum quality requirements in terms of details, bit or colour depth and colour reproduction. Such sound digital reproductions are increasingly available on the websites of museums, archives and other heritage institutions. For images of paintings and other artwork, for example, you can visit the website of the Rijksmuseum Amsterdam or the Web Gallery of Art. For posters of various European workers' movements, go to the International Institute of Social History of Europeana, and for prints, drawings, photographs and posters about Dutch history, visit the Atlas van Stolk collection (also available in English). These images generally come with high-quality descriptions (metadata), another important criterion for academic use in addition to the requirements mentioned before. Thousands of other high quality reproductions can be found via this Guide to Little-Known Image Collections with Millions of Free, Hi-Res Images.

When you are going to work with digital images (collecting existing images, editing images or digitising your own images) you need some basic knowledge of file formats, compression, resolution and colour depth / dynamic range. These are the main aspects that determine the quality of the image. For more information on these topics, see the page detailing the main technical aspects of digital images. When digitising images for academic use, we recommend making a master copy of optimal quality with as many colours and as high a resolution as possible in an uncompressed format. These images are the closest possible copy of the original and allow you to create detailed images of sections of the object. One example of a high resolution picture, where you can zoom in on any detail, is the painting En Bateau (Boating) by Édouard Manet, from The Met's digital collections. It is easy to convert a high-resolution, multi-coloured image into a lower resolution image with fewer colours (for use in a Word document or online publishing, for example), but the reverse is impossible.

For more information about this topic, please refer to the article The Basics of the creation of digital image reproductions by DEN. The Quality criteria section is particularly important.

Image editing software

Well-known photo processing software such as Paintshop Pro and Photoshop can be used to edit and convert images in various ways. However, the licences for this software are rather expensive. Operating systems such as Apple / Mac OS and Windows also include standard programmes to view and/or edit images. However, these programmes boast significantly fewer features. A lot of suitable software can be found on line, much of it as freeware. Irfanview, for example, is a program with many basic features (for Windows only). The freeware program GIMP offers a lot of possibilities for (semi-) professional image editing, but has a fairly steep learning curve. Online image editing software is also becoming increasingly advanced, as can be seen from Pixlr, for example. However, uploading images always means that your image files are stored on an external web server. In these cases, you must always find out which rights you are granting to the server owner to use the material. From an academic point of view, these online programs are not preferred.

Digital images and copyright

Generally speaking, you need permission from the copyright holder for every image you use. Copyright expires if the creator or photographer of an image died more than 70 years ago. This means you cannot just download, use and publicize images, unless you have been granted explicit permission to do so. Always check which rules apply to any website offering images you want to use (you can often find them under a 'Copyright' or 'Conditions of Use' link). A website might indicate that images may be reused, or used for specific purposes or under certain conditions.

For example, academic usage of copyrighted materials is often covered by a "fair-use" policy, which means that you need no permission from the creator to use the image. It is important, however, to find out whether a "fair-use" policy is actually in place. Obviously, you must always cite your sources.

In case of Creative Commons (CC) the author authorises others to use, share and edit their work (digitally) by default. There are some conditions attached, which are indicated by a code.

Other topics in this section: Technical aspects