Densmap and xpm2ps commands

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Currently, I used gmx-densamp to get the 2D density of my desired atoms. As all you know, two separate outcomes can be taken. First, output.dat, which includes data in the matrix form, and the second one is output.xpm. My problem is when I check the data of output.dat and compare it with the color bar of output.esp (obtained by applying xpm2ps), it seems that there is a conversion factor for data. For example: if the maximum data in the .dat file is 1500, it is converted to another value of 20 in the color bar (color bar: 0-20). However, when I look at the most prevalent value in the .dat file, for example, 750, the dominant color is not 10 ( x=750/(1500/20)). In fact, it seems that there is no linear relationship between converted data for visualizing in .eps format.

Could you please help me to understand which function is used for the conversion of the data in the .dat to the data used in the .esp?


This sounds strange. xpm2ps does not conversion at all, it simply computes the minimum and maximum value of the data and uses that to make a linear colormap and scale.