Scaling an image without changing number of pixels

[davelines]

Hi all,

I am having a bit of trouble scaling an image using ImageJ.

I have 2 images of the same object, both 512 x 512, however one image is in effect taken from closer to the object, so the total scale is 350mmx350mm, the second image is in effect taken from further away and it's scale is 500mmx500mm.

I would like to find a way of scaling (or maybe it is even a case of zooming) so that the 350mmx350mm image will overlap perfectly onto the 500mmx500mm image, however it is very important that the image remains 512x512 pixels.

There is possibly a really easy solution to this, however so far all my attempts have resulted in the number of pixels changing.

I really appreciate any help you could give me.

Many thanks,

Dave Lines

[John Oreopoulos]

Hi Dave,

Try this: You want to overlay the smaller sized image on the bigger  
one. The 350x350 mm image covers a smaller central portion of the  
larger image, so this image needs to decrease in size and then be  
fitted to 512x512 pixels with blank space around so it can overlay on  
500x500 mm image. The scaling factor between your two images is 0.7  
(350/500). Use the Image->Scale function to decrease the size of the  
350x350 mm image using this factor (allow the number of pixels to  
decrease to 358x358 pixels and use interpolation). Now select all on  
the new image (Edit->Selection->Select All) and choose Edit->Cut.  
Create a new blank 512x512 image (File->New Image). Click Edit->paste  
and your 358x358 pixel image will be pasted in the centre of this new  
blank 512x512 image. Use the image threshold commands to set the  
pixel value of the blank areas to NaN. Now you can overlay this image  
onto the original 512x512 500x500mm image. You might have to shift  
one image relative to the other a bit to get a perfect overlay (Use  
Image->Translate or some other ImageJ plugin that looks for optimum  
overlay).

John Oreopoulos


On 29-May-09, at 6:43 AM, davelines wrote:

> Hi all,
>
> I am having a bit of trouble scaling an image using ImageJ.
>
> I have 2 images of the same object, both 512 x 512, however one  
> image is in
> effect taken from closer to the object, so the total scale is  
> 350mmx350mm,
> the second image is in effect taken from further away and it's  
> scale is
> 500mmx500mm.
>
> I would like to find a way of scaling (or maybe it is even a case of
> zooming) so that the 350mmx350mm image will overlap perfectly onto the
> 500mmx500mm image, however it is very important that the image remains
> 512x512 pixels.
>
> There is possibly a really easy solution to this, however so far  
> all my
> attempts have resulted in the number of pixels changing.
>
> I really appreciate any help you could give me.
>
> Many thanks,
>
> Dave Lines
> --
> View this message in context: http://n2.nabble.com/Scaling-an-image- 
> without-changing-number-of-pixels-tp2993200p2993200.html
> Sent from the ImageJ mailing list archive at Nabble.com.

[Stephan Saalfeld]

Hi Dave,

if the scale is known to you and all you want is just applying it, then

1. scale by 350/500 or 500/350
2. change the canvas size to 512x512

If your images show really the same or a very similar looking object, in
Fiji, there is a plugin that uses SIFT features for automatic alignment
in presence of scale disparity.  Make a stack from your images and call
"Plugins -> Registration -> Linear Stack Alignment with SIFT", select
"Similarity" as transformation and press OK.  Alternatively, on both
independently opened images, use one of the plugins under "Plugins ->
Feature Extraction" to identify landmark correspondences (or click some
manually) and then "Plugins -> Transform -> Landmark Correspondences".
Again, "Similarity" is the transformation that includes isotropic scale.

Best regards,
Stephan


On Fri, 2009-05-29 at 03:43 -0700, davelines wrote:

> Hi all,
>
> I am having a bit of trouble scaling an image using ImageJ.
>
> I have 2 images of the same object, both 512 x 512, however one image is in
> effect taken from closer to the object, so the total scale is 350mmx350mm,
> the second image is in effect taken from further away and it's scale is
> 500mmx500mm.
>
> I would like to find a way of scaling (or maybe it is even a case of
> zooming) so that the 350mmx350mm image will overlap perfectly onto the
> 500mmx500mm image, however it is very important that the image remains
> 512x512 pixels.
>
> There is possibly a really easy solution to this, however so far all my
> attempts have resulted in the number of pixels changing.
>
> I really appreciate any help you could give me.
>
> Many thanks,
>
> Dave Lines