A question about LUT tables

[Pedro J CamelloDr Pedro J Camello]

I need to apply a common LUT to different images that will be obtained after some processing. My goal is to use that LUT to compare visually tens of images, but I don´t know the max and min values of the images (I just have a guess).

Instead of creating a custom LUT with my desired min and max values I was thinking of introducing in every image a pixel with given min and another pixel with a given max value. Then I could use any of the standard LUTs to compare all the images provided the LUT take my min and max values.

My question is, how do LUT tables "map" to the real pixel values of an image? Is enough to have a single pixel in the image with a min/max value to be used by the LUT?, or is needed for a value to reach a miimal percentage of the pixel population frequency to be used as min/max?

Thanks in advance

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[Peter Haub]

Hi Pedro,
not sure if there is a misunderstanding.

Color LUTs are mapping 'new' colors to each pixels intensity value. This
is independent from the number of image pixels with the same intensity.
E.g.:   A 8bit LUT contains a table with 256 entries for the intensity
values from 0 to 255. Each entry assigns an RGB color to his 8bit
grayscale value.
If you apply this LUT to an image containing only the value 120 then the
resulting image only contains the RGB color of the entry 120 of the LUT
table.

If you apply a color LUT to an image WITHOUT adjusting the display range
with the Brightness/Contrast... command then you can use any of the
standard LUTs to compare all your images.
(Adjusting the display range of your images with the
Brightness/Contrast... command will change the displayed intensity based
on the individual Min / Max values in each image.)

More information you can find in the section 'Pseudocolor Images' in the
IJ user guide
http://imagej.nih.gov/ij/docs/guide/user-guide.pdf

or in section '1.3.2    Mapping colours to pixels' of Peter Bankheads guide
http://blogs.qub.ac.uk/ccbg/files/2013/06/Analyzing_fluorescence_microscopy_images.pdf

Peter

On 29.01.2014 23:33, Pedro J Camello wrote:

> I need to apply a common LUT to different images that will be obtained after some processing. My goal is to use that LUT to compare visually tens of images, but I don´t know the max and min values of the images (I just have a guess).
>
> Instead of creating a custom LUT with my desired min and max values I was thinking of introducing in every image a pixel with given min and another pixel with a given max value. Then I could use any of the standard LUTs to compare all the images provided the LUT take my min and max values.
>
> My question is, how do LUT tables "map" to the real pixel values of an image? Is enough to have a single pixel in the image with a min/max value to be used by the LUT?, or is needed for a value to reach a miimal percentage of the pixel population frequency to be used as min/max?
>
> Thanks in advance
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html

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