How to calculate the PPI from Resolution X and Y?

[Pubudu Kodikara]

Right now im building a photo hosting website. I tried to get the resolution of the images we upload. Im familiar with the (PPI) resolution we use in Photoshop. When I tried to get the resolution of the image through RMagick, it gave me two values, `Resolution X` and `Resolution Y`. How can I calculate the exact resolution from the X and Y values?

[Astra.Xtreme]

https://www.sven.de/dpi/

[argonite]

PPI (Pixels per Inch) is not a resolution, but rather a conversion factor between resolution and real world size.

 

For example, Resolution X (which I assume is the number of horizontal pixels in the image) would be divided by the PPI of your medium (which can very depending on how large or small the image is displayed on screen/on paper) to yield how many horizontal inches the image will take up in real life.

 

You can use Resolution X and Y directly in your website.

[Pubudu Kodikara]

PPI (Pixels per Inch) is not a resolution, but rather a conversion factor between resolution and real world size.

 

For example, Resolution X (which I assume is the number of horizontal pixels in the image) would be divided by the PPI of your medium (which can very depending on how large or small the image is displayed on screen/on paper) to yield how many horizontal inches the image will take up in real life.

 

You can use Resolution X and Y directly in your website.

 

Now in major photo websites like dreamstime (http://www.dreamstime.com/editorial-photo-big-ben-sunset-picture-across-thames-image47178531) and istockphoto (http://www.istockphoto.com/photo/businessman-using-a-modern-interface-33108180?st=11a5423) they use DPI! How to convert the resolutions X and Y to DPI? or use PPI? Sorry im really confused!

[Nick H. Supervisor]

Sorry im really confused!

DPI (Dots per Inch) is for printing, I believe. PPI (Pixels per Inch) is for screen resolutions. But I'm no web designer, so I could be wrong.

[vcfan]

 How to convert the resolutions X and Y to DPI? or use PPI? Sorry im really confused!

 

you need the actual size of either the x or y axis, as well as resolution.

 

 

resolution x(pixels) / size x(inches) = PPI

 

or

 

resolution y(pixels) / size y(inches) = PPI.

[Pubudu Kodikara]

you need the actual size of either the x or y axis, as well as resolution.

 

 

resolution x(pixels) / size x(inches) = PPI

 

or

 

resolution y(pixels) / size y(inches) = PPI.

 

Ok that gives us two values, resolution Y and resolution X. How to take it into one value? Normally we show one value as the resolution.

[Torolol]

since 640x480 vga and beyond, we usually have square (1:1) aspect ratio pixels, so PPI for X or Y axis should be the same.

[vcfan]

Ok that gives us two values, resolution Y and resolution X. How to take it into one value? Normally we show one value as the resolution.

x and y just represent the amount of pixels on each axis line.

 

1280x720 resolution = 1280 pixels width (X) x 720 pixels height(Y)

 

calculating the PPI, you can use either x or y axis as long as you have square pixels(most likely).

[The_Decryptor Veteran]

ImageMagick (At least the CLI apps) seem to give the resolution in undefined units, no idea what RMagick does, but you might need to tell it to coerce the value into something useful.

A screenshot from my mac shows as "Resolution: 56.69x56.69", which is useless. Forcing it to use PPI gives me "Resolution: 143.99x143.99", which is still wrong (Apples fault), but it's at least useful.

[The Evil Overlord]

Right now im building a photo hosting website. I tried to get the resolution of the images we upload. Im familiar with the (PPI) resolution we use in Photoshop. When I tried to get the resolution of the image through RMagick, it gave me two values, `Resolution X` and `Resolution Y`. How can I calculate the exact resolution from the X and Y values?

At the risk of asking a silly question.... Isn't the answer X multiplied by Y?