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: http://xmm.vilspa.esa.es/sas/7.1.0/doc/colimplot/node7.html
Дата изменения: Mon Jul 9 04:33:12 2007 Дата индексирования: Sat Dec 22 11:12:28 2007 Кодировка: Поисковые слова: релятивистское движение |
It is desirable that the output image should look `right'. This is a psychological term and therefore has a degree of slipperiness of definition. However to my eye the colour scheme that looks best is what might be described as a `thermal' one, ie one in which cool objects (objects with a long-wavelength excess) are coloured red and hot objects blue, with the intermediate sequence going from red through yellow and white to blue. Greens and purples look wrong to my eye, in excess anyway. So the next part of the colour manipulations is to ensure that all colours fall on this `thermal' sequence. This is not difficult in the case that 2 input images are supplied, since these 2 degrees of freedom can fairly easily be mapped onto the 2 degrees of freedom, namely brightness and temperature (or analogue thereof), of the `thermal' scheme. But where there are 3 input images, one of the three degrees of input freedom must to a large degree be thrown away. (The three-image facility is retained however because there may be occasions when one wants the weird colours.)
The details of processing are probably not of much interest to the user; more important to know is that this forcing is controlled by the parameters weirdness, heat and heatspread. A weirdness value of 0 causes nothing to be done to the data; a value of -1 forces all pixels to have strictly thermal colours; whereas a value of +1 does the opposite, ie none of the consequent pixel colours are `thermal', they are all strange purples, greens and cyans. The parameter heat shifts colours along the thermal sequence: at heat = -1 all colours go to red, at +1 they are all blue, with again 0 having no effect. The third parameter, heatspread, stretches (positive values) or compresses (negaive values) colours along the thermal sequence.
At the end of this processing, each pixel is associated with a triplet of red, green and blue (RGB) values, each of which can have a value between 0 and 1.