Get the resolution of a jpeg image using C# and the .NET Environment?

Question

Our clients will be uploading images to be printed on their documents and we have been asked to come up with a way to get the resolution of the image in order to warn them if the image has too low of a resolution and will look pixalated in the end-product

If it comes to it we could also go with the dimensions if anyone knows how to get those but the resolution would be preferred

Thank you

Answer 1

System.Drawing.Image

Image newImage = Image.FromFile("SampImag.jpg");
newImage.HorizontalResolution

Answer 2

It depends what you are looking for... if you want the DPI of the image then you are looking for the HorizontalResolution which is the DPI of the image.

Image i = Image.FromFile(@"fileName.jpg");
i.HorizontalResolution;

If you want to figure out how large the image is then you need to calculate the measurements of the image which is:

int docHeight = (i.Height / i.VerticalResolution);
int docWidth = (i.Width / i.HorizontalResolution);

This will give you the document height and width in inches which you could then compare to the min size needed.

Answer 3

DPI take sense when printing only. 72dpi is the Mac standard and 96dpi is the Windows standard. Screen resolution only takes pixels into account, so a 72dpi 800x600 jpeg is the same screen resolution than a 96dpi 800x600 pixels.

Back to the '80s, Mac used 72dpi screen/print resolution to fit the screen/print size, so when you had an image on screen at 1:1, it correspond to the same size on the printer. Windows increased the screen resolution to 96dpi to have better font display.. but as a consequence, the screen image doesn't fit the printed size anymore.

So, for web project, don't bother with DPI if the image isn't for print; 72dpi, 96dpi, even 1200dpi should display the same.