Re: IR images index scale not linear and disjunct help?!

Posted by Gabriel Landini on Nov 29, 2009; 9:26am
URL: http://imagej.273.s1.nabble.com/IR-images-index-scale-not-linear-and-disjunct-help-tp3690302p3690306.html

On Saturday 28 November 2009, you wrote:
> Thank you for the reply, much appreciated.  I read about that so I did make
>  a custom lookup table. Unless I did something wrong. This is what I did: I
>  exported all the RGB values in order of the scale bar and then made a
>  custom look up table in order of the scale bar.  It helped some, making
>  the scale more linear but then right at the higher temperatures the scale
>  bar is still disjunct even with the lookup table.  I will try to attach an
>  image, maybe that would help.

It is not clear to me what sort of image you are dealing with, Here I assume
that the original is RGB.

My suggestion was to *recode* the pixel values to the indexes of the scale
bar.

Create a greyscale image of the same dimensions.
Now for all the entries in the scale bar of the original (asuming that the
colours are not repeated):
If red (255, 0 , 0) is the *first* colour, set all pixels with those values in
the RGB image to colour 0 (index=0) in the greyscale image.
Next colour is orange (let's say 255, 128, 0), put all pixels with that colour
to value 1 in the greyscale image and so on for the rest of the LUT entries
(256 in total).

Now you have an image which has intensity in the same order of the original
colour lut entries. You can now to apply a calibration to it using the
intensity of the scale bar. The new scale bar in your image should have an
intensity profile which is a ramp with no discontinuities from 0 to 255.

G.