[Insight-users] Intensity-based registration with low contrast images.

[Luis Ibanez]

Hi Vikren,

Thanks for the clear description of your problem and for posting the
images in an accessible place.

The problem in your case, is not the low contrast of the images
(although that certainly doesn't help...). The main problem is
related to how these images have been composed.

--

I just ran on them the example ImageRegistration9
(without modifications), an obtained a reasonable registration.

Looking closer at your images, the problem is that you seem to have
copy/pasted an image on top of a larger canvas.

That is, your images are of size 512x512, with a background of value 0.
Insight this region, there is a rectangle from (25,23) to (488,488) at
a intensity level close to 20 at the top, and with a gradient that
grows upto 45 at the bottom of the image.

Inside that region you have the projection of the head.


The rectangular region on the background is preventing the registration
from being driven by the data from pixels inside the head.


You can get rid of this problem in several ways.


   a) you can crop the images in order to contain only the
      region (24,24) to (488,488) before you feed the images
      into the registration.

or


   b) inside the registration you can set the FixedImageRegion
      to the region (24,24) to (488,488).



   Regards,


       Luis

----------------------
Vikren Sarkar wrote:
> Greetings,
>  
> I am trying to see if it is possible to perform intensity-based 
> registration on some very low contrast images that I have. I tried 
> posting this question a few days ago but realize there were some 
> problems with the website I was using. Hopefully photobucket will be 
> better. The following two images were acquired using an electronic 
> portal imaging device. The only difference is that one image is 
> translated compared to the other.
>  
> File 1 : http://i336.photobucket.com/albums/n333/poohvee/fixed.jpg
>  
> File 2 : http://i336.photobucket.com/albums/n333/poohvee/moving.jpg
>  
> Being new to ITK, I first started with several of the example 
> registration codes but none seem to work with the low contrast level. 
> Luis also suggested I try to run the images through edge detection. I 
> tried that approach as well as thresholding before registering but could 
> not get any results with any of the example registration codes. Finally, 
> I did try the example code using mutual information (example 2 in image 
> registration) and it did not work either.
>  
> Does anyone have any other suggestion I can use to artificially increase 
> the contrast before registering or can someone suggest a metric that 
> would be better suited for the task? The final aim would be to try to 
> use this with 3D datasets but I would like to start with 2D. Thank you.
> 
> Vik
>  
> 
> 
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