How to calculate image dpi using resolution.

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Hi,

can any one tell me how to calculate image dpi by using resolution of an image?

what is the formula for the dpi calculation?

please help me.

Thank you.

What I have tried:

VB

Dim Image As Image = Image.FromFile(Image_Path)
Dim unit As GraphicsUnit = GraphicsUnit.Point
Dim rect As RectangleF = Image.GetBounds(unit)
Dim hres As Single = Image.HorizontalResolution
Dim vres As Single = Image.VerticalResolution

Posted 8-May-16 21:22pm

kasunthilina

Updated 9-May-16 0:56am

Patrice T

v4

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Comments

Peter_in_2780 9-May-16 3:33am

"dpi" = dots per inch, i.e. pixels per 25.4mm. This is a function of the display hardware, not the image. Some images may contain hints as to the intended display size/resolution, but they are only ever hints.

kasunthilina 9-May-16 5:34am

'found it.
Dim dx As Single, dy As Single
Dim imageFile1 As Image = Image.FromFile(SourcePath)
Dim g As Graphics = Graphics.FromImage(imageFile1)

Try
dx = g.DpiX '// selected file DPI
dy = g.DpiY

Finally
g.Dispose()
End Try

3 solutions

Solution 1

The Image.HorizontalResolution Property (System.Drawing)[^] and Image.VerticalResolution Property (System.Drawing)[^] already gives you the DPI (horizontal and vertical).
However, as Peter_in_2780 pointed out, that is just a hint.

Posted 8-May-16 22:09pm

CPallini

Solution 2

Quote:
can any one tell me how to calculate image dpi by using resolution of an image?

You don't one does not imply the other.

HorizontalResolution and VerticalResolution are image size in pixels.
The DPI setting is used to reduce the size of physical printing.
printed Width = HorizontalResolution / DPI
printed Height = VerticalResolution / DPI

Understanding DPI, Resolution and Print vs. Web Images[^]

Posted 8-May-16 22:47pm

Patrice T

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kasunthilina · Accepted Answer · 2016-05-09T00:45:00

Solution 3

C#

'found it.
Dim dx As Single, dy As Single
Dim imageFile1 As Image = Image.FromFile(SourcePath)
Dim g As Graphics = Graphics.FromImage(imageFile1)

Try
dx = g.DpiX '// selected file DPI
dy = g.DpiY

Finally
g.Dispose()
End Try

Posted 9-May-16 0:45am

kasunthilina

Comments

Patrice T 9-May-16 7:00am

Use Accept answer to close the question when solved.

kasunthilina 9-May-16 7:11am

thank you for the help