MATLAB: How to improve pixel resolution in an image

imageImage Processing ToolboxMATLABpixelresizeresolution

Hi all

I have a 951*951 matrix of image after reconstruction. I want to resize them into 512*512 in Matlab.

At the same time, the pixel resolution should be changed to about 2 pixels/mm,which at the moment is 1 pixel /mm (i.e., width of image= 512mm snd ht- 512mm).

I tried with 'imresize'-I could change the size only. Is it possible to reduce the width & height of the image to be 250 mm while maintaining the same pixel numbers (512*512). Is there any way to do it? Also I wonder whether 'imresize' will distort the image quality( I mean making the image more softer)

Best Answer

If you have a 951 wide image with 1 mm per pixel, then the field of view is 951 mm. Now if you reduce this to 512 pixels, the field of view is still the same - 951 mm - so the resolution is now 951 mm / 512 pixels = 1.86 mm per pixel.

If you want 250 mm, then you need to crop out a 250x250 mm chunk from the 951x951 image. So use imcrop to extract a rectangle of that size from the desired location. Once you've done that, you can resize from 250 by 250 pixels to 512 x 512 pixels. Your field of view will stay 250 mm since you are still looking at the same stuff, but it will just have a different image matrix size (512x512). The image may look softer since you are more than doubling the size of a fixed 250x250 mm subimage.

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MATLAB: How to make an auto cropping command

I thought I already gave you code for this. Basically you threshold it, then call bwareafilt() to extract the largest blob. Then call regionprops() to get the bounding box. Then reassign the last element of the bounding box to be whatever height you want, then call imcrop(). Try it. Here's a start

binaryImage = bwareafilt(grayImage > 0, 1);
props = regionprops(binaryImage, 'BoundingBox');
bb = props.BoundingBox;
bb(end) = 100;  % Whatever height you want.
croppedImage = imcrop(grayImage, bb);
imshow(croppedImage);

MATLAB: How to increase number of rows and cols without changing the image size

That's correct. How big you consider a pixel to be in "real world units" depends on the calibration you're using. It could be one micron, one kilometer, or one light year. If I have a length that is 1 meter long in MATLAB, and it happens to be 1000 pixels long, then I can multiply the number ob pixels by 1/1000 to get the distance in meters. If I resize the image so that that length is now 2000 pixels long, then my calibration factor will have to be 1/2000 now in order to still get a real world distance of one meter again.

Best Answer

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