Convert Pixels to Inches and vice versa in C#

Question

I am looking to convert pixes to inches and vice versa. I understand that I need DPI, but I am not sure how to get this information (e.g. I don't have the Graphics object, so that's not an option).

Is there a way?

Answer 1

On a video device, any answer to this question is typically not very accurate. The easiest example to use to see why this is the case is a projector. The output resolution is, say, 1024x768, but the DPI varies by how far away the screen is from the projector apeture. WPF, for example, always assumes 96 DPI on a video device.

Presuming you still need an answer, regardless of the accuracy, and you don't have a Graphics object, you can create one from the screen with some P/Invoke and get the answer from it.

Single xDpi, yDpi;

IntPtr dc = GetDC(IntPtr.Zero);

using(Graphics g = Graphics.FromHdc(dc))
{
    xDpi = g.DpiX;
    yDpi = g.DpiY;
}

if (ReleaseDC(IntPtr.Zero) != 0)
{
    // GetLastError and handle...
}


[DllImport("user32.dll")]
private static extern IntPtr GetDC(IntPtr hwnd);    
[DllImport("user32.dll")]
private static extern Int32 ReleaseDC(IntPtr hwnd);