What is the image editor's resolution tool for? - image

I have an image that is 320 x 482 pixels size and 72 PPI. I can change the image resolution with GIMP for example, but why would I use it if the images suits its pixel size for each display pixel size? I mean, an image changes its size in inches depending on the display density, right? So why would I want to change the PPI of an image, that doesn't make sense to me, although I understand that GIMP and any other image editors wouldn't put this feature for nothing.
PS: I tried to change the resolution of some images and compare it with the original image and apparently nothing happened but the size in inch of the image.

An image's DPI is defined by the capturing hardware and will impact it's size when printed out.
Changing the resolution won't change the number of pixels in the image.

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CSS3 Hero Image: Whats the best pixel dimension and Image Size for a full screen responsive background?

CSS3 Hero Image question:
Whats the best pixel dimension and Image Size for a full screen responsive background?
Whenever I use the cover property, it always seems to miss out most the image.
Thanks,
Steve
Used photoshop to crop the image to a 16:9 ratio, 1920 x 1080 pixel dimension for best image quality. Seems to work well with my website, hopefully the file size (507kb) won't be an issue on page loading response times.
Also, consider running your images through a compressor, which can greatly reduce their file size.
https://compressor.io

Calculate DPI of image

I have an image on a canvas. That image will be resized by user.After that, the canvas content will pe printed at a specific dimension.
I want to calculate the DPI of the resized image, so i can tell the user if he resized to much and the printed quality will be affected.
Does someone know a formula for this?
DPI means dots per inch.
Divide the pixel size of the image with its physical dimensions in inches.

Retina images that are not quite double size

I've read the book Retinafy Me. This basically says double the size of images. When it is then displayed on a retina screen at half the image size it will look great.
My problem is that the original images I have can't be doubled in size. i.e. the images are 750px wide. They are to be displayed 500px wide. What do I do? Is a x1.5 image better looking that a x1 image (on a retina screen) or is it just needlessly adding to the file size?
I've tried using the x1.5 images (750px scaled down to 500px) and the images looked good on a retina screen in the Apple store where I checked them out. But I couldn't do a definative comparison, I don't have a retina screen of my own and I can't find any info about it anywhere.
A pixel is still a pixel on a retina screen. The difference is simply that a retina screen uses 4 pixels to display one, if they have no additional information such as more pixels. This is why the suggestion is to double the image size.
Essentially your image will be rendered by stretching it to 1000px wide. When stretched, a 750px wide image will still look better than a 500px wide image. You can try this for yourself in Paint.
There is a pretty good explanation of how it works on http://crypt.codemancers.com/posts/2013-11-03-image-rendering-on-hd-screens/
Hope this helps.

Matlab GUIDE blurs image?

my plan is implementing an image in a Matlab GUIDE figure. Somehow the output is always blurred (see screenshot). On the left you can see the image in Photoshop on the right in Matlab - notice how the font and other parts become blurred.
I experimented with JPEG and PNG file formats (no compression), I also tried various pixel sizes(resolutions smaller, same and bigger as the actual position of the image) and DPI(values between 30-300) settings, because I expected some scaling issue. Somehow I am stuck - Looking forward to your input!
Thank you,
Florian
Screenshot of the issue: http://s1.bild.me/bilder/260513/6875414Screen_Shot_2014-06-29_at_23.19.34.png
Most probably the reason for the blur is interpolation.
If the axis size you allocated for the image is different from the size of the image MATLAB will resize the image to occupy the whole area.
In order to prevent any interpolation you must set the axis dimension to be the image dimension.

In Magento how can i maintain image quality when i re-size the image with lower pixel

I want to show the image as good it is in it's actual size even when i re-size it with lower image pixel.
what? If you resize the picture, the pixel-count is lowered. There is no way to resize an image without loosing quality.

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