Reading and changing the DPI of an image in ASP with csImageLite

The pixel density of an image can be read or set with csImageLite. The property is DPI and it is always measured in dots per inch. The functions DPMToDPI and DPIToDPM are available for converting to and from metric. There are two properties, XDPI and to specify the X and Y pixel densities.

The following code fragment loads an image and displays the pixel density.

Image.ReadFile "c:\images\photo.jpg"
Response.Write Image.DPI

The next fragment sets the DPI to 100

Image.ReadFile "c:\images\old.jpg"
Image.XDPI = 100
Image.YDPI = 100
Image.WriteFile "c:\images\new.jpg"

Not all formats store a pixel density value and this includes GIF. Some image editing software will show a value for DPI when opening one of these images but they are only selecting a default. The GIF format does not have anywhere to store this value. csImageLite can read and write pixel density in PNG images but this is an extension to the format that not all software supports.


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