How to add a property to a PNG file

Question

I have a PNG file to which i want to add the properties

1. Pixels per unit, X axis
2. Pixels per unit, Y axis
3. Unit specifier: meters

These properties are explained in the PNG specification: http://www.w3.org/TR/PNG-Chunks.html

I have programmatically read the properties of the png to check if the properties exists, so that i can set the value for this properties, but i could not see this properties in the png file. (Refer pixel-per-unit.JPG)

How can we add properties to the png file?

regards

Answer 1

I think you are looking for SetPropertyItem. You can find the property ids here

You would use the property id to get and then set the property item for your meta-data.

EDIT

The three id's that you need (I think) are:

1. 0x5111 - Pixel Per Unit X
2. 0x5112 - Pixel Per Unit Y
3. 0x5110 - Pixel Unit