How to Change Background Image Transparency?

How do I change the “Transparency” property of a background image (as shown below)?

image.png (8.1 KB)

@bingxie,
Thank you for posting your requirements.

The background transparency is changed by using image effects. The following code snippet shows you how to change the background transparency.

var transparencyValue = 30; // for example

// Get a collection of picture transform operations.
var imageTransform = slide.Background.FillFormat.PictureFillFormat.Picture.ImageTransform;
                
// Find a transparency effect with fixed percentage.
var transparencyOperation = null as AlphaModulateFixed;
foreach (var operation in imageTransform)
{
    if (operation is AlphaModulateFixed alphaModulateFixed)
    {
        transparencyOperation = alphaModulateFixed;
        break;
    }
}

// Set the new transparency value.
if (transparencyOperation == null)
{
    imageTransform.AddAlphaModulateFixedEffect(100 - transparencyValue);
}
else
{
    transparencyOperation.Amount = (100 - transparencyValue);
}