The Meaning Of Some Common Terms
Following is a brief description of what some of the most common terms in digital restoration mean. This may help you when talking to someone about having a digital restoration performed on your image.
Pixels – are considered as the smallest element of an image.
Resolution – if referred to in scanning, is the number of dots per inch (DPI) that your scanner produces when making a copy of your image. The higher the resolution, the more pixels per inch you have to work with, however there is a practical limit as to how high to scan an image. Up to a point, higher resolution provides a more distinct image (more information to work with) while the lower the resolution provides lesser detail and distinction. If the original image is small and it is destined to be enlarged you would want to scan at a higher resolution.
Digital Photographs – are produced by using a fixed number of colors appearing as a fixed number of squares or pixels. A camera with a higher mega-pixel number may produce an image with more fine detail then one with a smaller number of pixels. However, there is so much that goes into the making of a digital image within today’s cameras that this is really an over simplification.
Scanning – is a method where an image or document is converted to pixels for electronic transmission and display.
File Format – The file that is produced by the act of taking a picture digitally or by scanning into the computer. The file may be saved in various formats depending upon it final usage, such as JPG, TIFF, RAW, etc.
A JPG’s file, pronounced “j–pegs”, are images that have been stripped of some of their detail by compressing the file information in order to make smaller files and speed electronic transmission while providing smaller storage requirements.
The preferred file format for restoration of photographs is the TIFF, “Tag Image File Format”. TIFF allows for a wide range of different lossless compression schemes and color spaces. Thus making them ideal for digital restoration.
Bit Depth – is the name for the number of actual pieces of information which make up a digital image. Typically, most photos will have a bit depth of 8 bits per color channel. For example, if the image is in color, which is made up of three channels – red, blue and green – the bit depth is said to be 24 bits, which gives you a certain number of levels of information to work with when correcting an image. The preferred bit depth for digital restoration is 48 bits or 16 bits per channel. A higher bit depth doesn’t increase the number of pixels in an image, what it does is provide a greater level of precision in the way the tonal information is recorded by a camera or scanner. So, if you have 8 bits per channel you get a yield of 256 levels of information, while 16 bits per channel gives us 65,536 levels to work with, a pretty big difference.