Re: Thresholding help

Posted by Michael Doube on Oct 29, 2008; 9:02pm
URL: http://imagej.273.s1.nabble.com/Thresholding-help-tp3694620p3694623.html

Justin:

How about subtracting the background gradient from the image to improve
contrast?

Just take a 'background' image without any droplets and use
Process->Image Calculator, subtracting your background from the
droplets+background image.  I had a quick go on your example and greatly
improved the ability to discriminate the droplet contours.

Mike

Fabrice Senger wrote:

> Quoting Justin Walker <[hidden email]>:
>
>> I have a series of images of liquid droplets, which have very poor
>> contrast with the surrounding phase, due to the similarities in their
>> index of refraction.  I get enough contrast in my images to clearly see
>> the droplets, however, I can't pick them out with the threshold because
>> there is a slight gradient in the brightness of my lighting.  Link to a
>> sample image is below:
>>
>> http://www.chejrw.com/forum/test.tif
>>
>> Does anyone know of a way I can manipulate this image to be able to use
>> the 'measure particles' plugin to get the droplet sizes?  I can clearly
>> see the droplets, so surely there must be a way to make the computer
>> see them.
>>
>> Thanks everybody
>>
>> - Justin Walker
>
> As far I can see in your images, you can see the "contour" of the droplets.
> If you invert your image, this "contour" should appear bright in a dark
> background.
>
> This should help.
>
> Fabrice.