Very strange ppi of png [closed] - png

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I have some png files, and their ppi were 300.
Now I've change the ppi to 72, but the size of the pictures even became larger!
For example, a.png was 190k, 300ppi,
now it becomes 400+k, 72ppi, and it is always 320*460,
what's happening, how should I do?
I was meant to reduce the pictures's size..

ppi stands for 'pixels per inch'.
The equation for image size is NoOfPixels = NoOfInches * PixelsPerInch
Or NoOfInches = NoOfPixels/PixelsPerInch
So reducing the ppi will increase the 'physical' size of the image.
To reduce the size of the image you need to squash more pixels into each image of 'physical' space, so increase the ppi

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i want to display some data into a label but it is not showing the full text. How can i fix this behaviour ? I set the lines to 0, but is still not working.
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I want to determine area of circular object in image below using MATLAB. Can someone explain codes for doing that? I got thresholded image but I did not proceed more.
If the binary image is img, and it contains only values 0 (background) and 1 (object), or it is a logical array containing true and false, and all the object pixels are considered part of the object, then sum(img(:)) is the area of the object in pixels.
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How to change Matlab's scaling process when not Native? [closed]

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I would like to change the downsampling method or the process by which Matlab changes picture when resolution is not native.
I am especially interested in the scaling methods which are suitable for scientific computing in grayscale.
Default Matlab 2016a's warning whatever the scaling is
Warning: Image is too big to fit on screen; displaying at 50%.
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For instant:
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I have an image which I have converted to a binary mask.
My regions of interest are those with 1 in the mask.
I want to find the coordinates of these regions,
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I am doing an image processing project. In my project there is an GUI file that reads an image and processing it for segmentation. while reading an image file, initially it is checking the size of that image... However, I don't understand what the function I=[m x n x 4] really means. Could someone explain this to me?
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