Image capture is the moment the physical object is turned digital, by the process of being scanned or photographed. How you capture the item and how you save the data effects the longevity and functionality of the digital asset.
Remember, the golden rule is to only do this work once and to make sure that you do it right, so that time and efforts are not wasted and the work does not need to be done again.
The National Library of Australia has image capture standards that advise on the tonal resolution (the number of bits per pixel) and spatial resolution (the number of pixels per inch) for different types of 2D materials. These standards have been developed over many years of working with collections.
Image file formats
There are various formats for saving images, but the two main ones are:
- JPG or JPEG - Joint Photographic Experts Group. In this format the information is highly compressed and ‘unnecessary’ information is removed from the item to make it smaller and save space. This changes the digital asset slightly from the original analogue asset if it is a scanned asset, but these changes are generally not able to be seen by the eye.
- TIFF – Tagged Image File Format. This format is uncompressed, meaning that no information has been removed from the digital asset, so it should match the original analogue item as closely as possible.
JPG and other file formats like it, are referred to as ’lossy’ because of the information that is lost when the digital asset is compressed.
TIFF files are referred to as ’lossless’, as every piece of detail about that digital asset has been retained in the scan. This is why TIFF files are considered Master Files.
Saving digital images as TIFF files is the recommend standard as it preserves as much information and data within that image, as it possibly can. JPG files may be smaller, but detail and information will be lost from the original image.
When other versions are needed, copies can be made from the Master and saved in the appropriate format for their intended use. For example, TIFF files are not suitable for use on the internet. So, when an organisation wishes to post an image of an item to social media, a JPG copy can be made from the Master File for use online. The Master File remains unchanged. Importantly, the item has been captured once and handled only once.