information about LUTs and image manipulation

[Bill Saidel]

Hi Imagers,
     In my work with brain images, I convert from a 256-gray LUT to a  
16-gray LUT. The graphic display of the new LUT works fine.

When I save the 16 gray'ed image and reopen the recently-saved 16 gray  
level image, the display uses 16 levels but the value of each pixel  
corresponds to a value in a 256 gray LUT. That is, the values of the  
pixels in the 16 level image are one of 255.

  What does it take to save the values of the pixels in the displayed  
16 gray level image as one of 16 values?

Thanks in advance for removing an iota of ignorance,

Bill Saidel
Biology
Rutgers-Camden

[Wayne Rasband]

> Hi Imagers,
>     In my work with brain images, I convert from a 256-gray LUT to a
> 16-gray LUT. The graphic display of the new LUT works fine.
>
> When I save the 16 gray'ed image and reopen the recently-saved 16 gray
> level image, the display uses 16 levels but the value of each pixel
> corresponds to a value in a 256 gray LUT. That is, the values of the
> pixels in the 16 level image are one of 255.
>
>  What does it take to save the values of the pixels in the displayed
> 16 gray level image as one of 16 values?

One way to do this is to convert the image to RGB using Image>Type>RGB
Color and then convert it back to grayscale using Image>Type>8-bit. You
can create a 16 gray LUT by clicking on "Set" in the Image>Color>Edit
LUT window and entering 16 as the "Number of Colors" and selecting
"Replication" for 'Scale Using".

-wayne