css using argb for opacity

I am attempting to apply a watermark (string) with some opacity (css attribute) to both an image and a pdf using itext.

For the pdf, I can simply use:

PdfGState gstate = new PdfGState();
gstate.FillOpacity = textOpacity;

Everything works fine. However, for the image, I am using:

Color color = Color.FromArgb(int alpha, Color color)

My question is how to convert css opacity to alpha?

I came across the formula: opacity = (255 - transparency) / 255.0

Is this correct? Because if my opacity is 1f (no opacity), the alpha will be 0 resulting in fully transparent text...

c#asp.netcssimage

Answer №1

The formula is slightly incorrect. In C#, the value range should be between 0 and 255, but you are using a range of 0 to 1. Therefore, the correct formula would be:

alpha = (int)(textOpacity*255);

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