The baseline offset is the number of counts generated by the detector when there is no light. Several sources of noise are always present, so it is impossible to have no counts. The main components of baseline offset are electronic offset, dark current, and readout noise. This acts to offset the baseline of the spectrum by an amount that is consistent across the pixels. Depending on the pixel, the value might be slightly different. These differences are called the Dark Signal Non-Uniformity (DSNU). Pixels that vary greatly from all the other pixels are considered defective and can be interpolated over when taking measurements. The baseline offset can be accounted for by taking a dark spectrum and subtracting it.
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