The image is located at the end of the DICOM file. The standard allows for 9 image formats, including monochrome (single color plane), 3 plane color, and JPEG compression. Additional options apply to each format. For the monochrome formats, data elements specify the number of bits allocated for each pixel, the number of bits used, and the position of the used bits in the allocated space.
The current version of Scan2MCP reads monochrome (MONOCHROME1 [minimum intensity white] and MONOCHROME2 [minimum black]) and lossless JPEG formats. It has only been tested with 8, 12, and 16 allocated bits per pixel with the same number of bits used.
A sub range of pixel values is used to produce a meaningful image. The sub range is defined by the window width W and window center C. Values between C - W/2 and C + W/2 are mapped to intensities, which in turn are mapped to shades of gray or colors as described next. Values outside the range are mapped to the range limits. The DICOM file contains recommended values for W and C. We provide methods for changing the values as discussed in the section on contrast controls.
The file may specify a value for the slope S and intercept b. If present and or , the pixel values V are changed to where V' is the pixel value stored in the file. The values of C and W are applied to the transformed pixel values V.
In the following, pixel values means the number stored in the file for each pixel, possibly modified by the slope and intercept. The pixel intensity is the quantity between 0 and 255 that is obtained after the application of C and W.
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