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From: Rise on 26 Apr 2010 19:21
Hi, all,

Am new to Matlab and image processing. I've been reading through the
many books that have been suggested to me, the posts here looking for
information and also surfing the net online. I am trying to figure out
how to phrase my questions, so please excuse my vagueness.

From what I gathered from one of the posts (http://groups.google.com/
group/comp.soft-sys.matlab/browse_thread/thread/982e03cbe1d0898f/
c150d869649e745f?lnk=gst&q=camera+calibration
+cropping#c150d869649e745f), it seems that if I crop an original 2D
image in an application such as Photoshop, it will change the
information in the 2D image (e.g., lighting, noise). If this is so, I
am assuming that my intrinsic camera parameters will be different as
well. Is this correct?

If yes, then is imresize() a better way of working with my 2D image so
that information is not changed? How can I work with my images so that
I can just focus on the object that is positioned approximately in the
middle of the image? (This is the reason why I was cropping in the
first place.)

Hope this makes sense. Thanks a bunch. - Rise
From: Rise on 26 Apr 2010 19:44
Ok, I think I found one answer to my questions below: Use the function
imcrop(). See Loren's blog at http://blogs.mathworks.com/loren/2007/10/16/tire-rotation/

As for the other questions, I guess it involves different algorithms
output different results. So with using Photoshop vs. imcrop() and
imresize(), I will have different information in my new images,
correct?

Thanks, will keep surfing and reading as much as I can before
posting.... - Rise

On Apr 26, 7:21 pm, Rise <riser...(a)gmail.com> wrote:
> Hi, all,
>
> Am new to Matlab and image processing. I've been reading through the
> many books that have been suggested to me, the posts here looking for
> information and also surfing the net online. I am trying to figure out
> how to phrase my questions, so please excuse my vagueness.
>
> From what I gathered from one of the posts (http://groups.google.com/
> group/comp.soft-sys.matlab/browse_thread/thread/982e03cbe1d0898f/
> c150d869649e745f?lnk=gst&q=camera+calibration
> +cropping#c150d869649e745f), it seems that if I crop an original 2D
> image in an application such as Photoshop, it will change the
> information in the 2D image (e.g., lighting, noise). If this is so, I
> am assuming that my intrinsic camera parameters will be different as
> well. Is this correct?
>
> If yes, then is imresize() a better way of working with my 2D image so
> that information is not changed? How can I work with my images so that
> I can just focus on the object that is positioned approximately in the
> middle of the image? (This is the reason why I was cropping in the
> first place.)
>
> Hope this makes sense. Thanks a bunch. - Rise

From: Image Analyst on 26 Apr 2010 20:41
Cropping in Photoshop will ONLY crop - it won't change anything else except maybe the EXIF metatag information if you save it as a new image, and the values slightly if you save it as a new jpeg because it has to calculate a new compression. Saving it as PNG, or some other uncompressed version won't change the pixel values. If you call resize, of course that will change the pixel values in both MATLAB and Photoshop because it has to block-average down, or interpolate up. But the resulting image won't look dramatically different than what you're expecting. For example it won't look like the scene lighting is way different. Noise will be different for resizing but not for cropping - makes sense if you think about what each process is doing.
From: Rise on 26 Apr 2010 20:49
Hi, Image Analyst,

It helps to talk to someone about my questions, and so many do I
have....Thank you so much for you reply! Sincerely, Rise
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