Digital imaging is the art of making digital images – photographs, printed texts, or artwork - through the use of a digital camera or image machine, or by scanning them as a document. Each image is compiled of a certain amount of pixels, which are then mapped onto a grid and stored in a sequence by a computer. Every pixel in an image is given a tonal value to determine its hue or color.
In digital imaging, the tonal value of each pixel is represented in binary code. The binary digits for each pixel are called "bits," which are read by the computer to determine the analog display of the image. The number of pixels-per-inch (ppi) is a good indicator of the resolution, which is the ability to distinguish the spatial detail of the digital image.
The bit-depth and pixel measurement of the picture relate to the colors viewable in the image, and determines the size of the image file on a computer. Images with only two pixel shades – black and white – are binary. Grayscale images are typically displayed in 8-bit mode, which is 256 shades of gray. In digital imaging 24-bit mode, which represents true color, is generally the maximum available mode due to monitor limitations. Both of these ranges extend beyond the sensitivity of the human naked eye.
The dynamic range of an image is the number of shades of gray or color that can be included in that image. It is the range of tone between the darkest and lightest colors. A higher dynamic range brings with it more potential shades represented but does not necessarily correlate with the amount of tones that are reproduced. An image may have a broad dynamic range, but a smaller amount of tones represented. Likewise, in digital imaging an image may have more tones, but not as wide of a dynamic range. This can have an effect on the details within the image.
There are a wide range of options for storing digital images on a computer. Some common ones include GIF, JPEG, TIFF, and BMP. GIF, or Graphics Interchange Format, has a bit-depth of 1-8 bitonal, grayscale or color. It is limited to a 256 color palette. JPEG, or Joint Photographic Experts Group, has a grayscale of 8 bits and a 24-bit color scale. JPEG is most often used on web pages. TIFF, or Tagged Image File Format, is commonly used for scientific imaging. It supports an 8-bit color palette and 8- to 16-bit grayscale. TIFF 6.0 can provide up to 64-bit color, but most TIFF readers will support only a maximum of 24-bit color.
