In this series dedicated to digital image, gray level images are the most common images used in ImageJ.
1. Introduction
Gray-level images - unlike the binary [Link] - contain shades of gray from black to white as shown in Fig. 1A,B and must not be mistaken with the binary image of Fig. 1C. |
| Fig. 1: Examples of images. From Top to Bottom: A,B) Gray-level images. C) This image only contains Black and White colors. It is a binary image. |
2. Bits per pixel and Dynamic range
In photography, the dynamic range [Wikipedia] corresponds to the luminance of the scene and is captured/converted by the digital camera. The limits of luminance range - that is the number of shades available in the digital image - is directly related to the number of bits allocated per pixel: 8, 16, and 32 bits.Just take the example of the 8-bit image where each pixel is defined by one byte ( 8 bits). Thus, the minimum value is ...
00000000 = 0
... and the maximum is ...
11111111 = 1x27+1x26+1x25+1x24+1x23+1x22+1x21+1x20 = 28-1 = 255
In this case, we have a maximum of 256 (from 0 to 255) different shades in a 8-bit image . For a scientific image, this is rather limited because most of the CCD or CMOS camera work with 12- or 16-bits precision. Thus, in a scientific project, we are working with 16-bits images with 65536 (216 from 0 to 65535) shades of gray.
Note: I have another post describing the 8-bit, 16-bit and 32-bit images [Link]
[TODO: Image with 8-bit, 4-bit, 3-bit, etc...]
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