This does not include storage in memory of the image itself, nor any of the other administrative data structures needed. Of note on this table is the use of some 22Mb for internal data when computing an HSI-Alpha correlated histogram on a pathological case 1280 x 1024 image. Every effort has been made in imhist to keep memory use to a minimum. This high use of memory for correlated histograms cannot be avoided without resorting to temporary files for data storage, and the attendant sever execution speed impact. Please note again that this table was produced for a pathological image that had a different color for every pixel.
Most images have considerably fewer colors.
In typical use, memory will not be a problem. Computation time for correlated histograms also goes up with the number of correlated fields, the size of the image, and the number of unique colors. The following table shows compute times running imhist on local disk on a Silicon Graphics Indigo using uncompressed RGB images. Column two gives the fields used in computing the histogram. Column three shows the number of unique colors found.