Re: Brightness & Contrast Adjustment Question

Posted by Wayne Rasband on Nov 17, 2006; 5:19pm
URL: http://imagej.273.s1.nabble.com/Brightness-Contrast-Adjustment-Question-tp3700994p3700997.html

> Just so I am sure I understand (I am an imaging newb :) ) this means
> that for DICOM images, ImageJ loads the "recommended" values for B&C
> from the DICOM header(metadata)?

That is correct.

> Another question, if the DICOM image is 16-bit, does ImageJ
> "resample/convert" the image to 8-bit to adjust the B&C values?

ImageJ has to create an 8-bit version of the image for display since
most video cards and monitors support no more than 8-bits per channel.
This 8-bit image is created by linearly mapping from the display range
to 0-255.

-wayne

> Thanks so much!
> Wayne Rasband <[hidden email]> wrote: When opening a DICOM, ImageJ set
> the display range based on the Window
> Center (0028,1050) and Window Width (0028,1051) tags. Click "Reset" in
> the B&C window and it sets the display range to the minimum and maximum
> pixel values. As an example, the File>Open Samples>CT image has a
> Window Center of 50 and Window Width of 500, so the display range is
> set to -200 to 300 (center-width/2 to center+width/2). Click "Reset"
> and the display range is set to -719 to 1402. Press 'h'
> Analyze/Histogram) and you will see that the minimum pixel value in the
> image is -719 and the maximum is 1402. To display the DICOM tags, press
> 'i' (Image>Show Info). Press 'r' (File>Revert) to revert to the
> original display range.
>
> -wayne
>
>
> On Nov 17, 2006, at 11:29 AM, Jason K wrote:
>
>> I am using 1.38A imageJ and I noticed something strange with the
>> Brightness & Contrast adjustment (Image menu -> Adjust ->
>> Brightness/Contrast) when viewing DICOM images.
>>
>> When you open the B&C window on a DICOM (CT, MRI, or X-ray) the
>> sliders for Brightness, Contrast, Minimum,and Maximum are already
>> adjusted.  Then, if you click the Reset button in this B&C window it
>> returns the sliders to a totally different position (likely centered).
>>
>> Why/How is imageJ starting B&C with the image already adjusted in the
>> B&C window?  Does ImageJ automatically do a B&C adjustment when a
>> DICOM image initially loads?
>>
>> Thanks in advance,
>>
>>
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>
>
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