How to decode tiff file and preserve opacity?

Fri, 03 Jul 2009 20:37:43 Z

By default, standard TiffBitmapDecoder decodes to flatten image with white background. All transparency converts to white. But if I save in Photoshop file in tiff format, with not recently used option, "Save Transparency", TiffBitmapDecoder converts fine and preserve opacity.

I need solution, how I can import all tiff files and preserve opacity, or how I can read alpha chanel or mask information from file to have ability add Opacity.Mask to Image?

How to decode tiff file and preserve opacity?

Sat, 04 Jul 2009 20:58:02 Z

Are you using the "PreservePixelFormat" create option on the TiffBitmapDecoder?

Mark Salsbery Microsoft MVP - Visual C++

How to decode tiff file and preserve opacity?

Sun, 05 Jul 2009 11:41:59 Z

Are you using the "PreservePixelFormat" create option on the TiffBitmapDecoder?

Mark Salsbery Microsoft MVP - Visual C++

Yes, but same result for BitmapCreateOptions.None

Stream imageStreamSource = new FileStream("C:/Users/*/*.tif", FileMode.Open, FileAccess.Read, FileShare.Read);
TiffBitmapDecoder decoder = new TiffBitmapDecoder(imageStreamSource, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
            
BitmapSource bitmapSource = decoder.Frames[0];
testImage.Source = bitmapSource;

How to decode tiff file and preserve opacity?

Mon, 06 Jul 2009 23:31:24 Z

Eric from the WIC team says this:

"The problem is that, when Photoshop saves a TIFF file, it handles alpha by using custom metadata which stores Photoshop’s proprietary layer information. If “save layers” is turned off, even Photoshop won’t recognize that the saved image has alpha.

The most standard way to support alpha in a TIFF file is to use an extra sample representing the alpha channel. By default, Photoshop doesn’t write this sample, so WIC has no good way of detecting that the image includes alpha. If the “Save transparency” option is checked in Photoshop, it will write the alpha channel, in which case WIC should recognize and display the alpha properly.

Given that Adobe’s default way of saving alpha is proprietary and based on the Photoshop layer system, most applications won’t detect the TIFF’s alpha unless the “Save transparency” option is checked (I confirmed with IrfanView, Picassa didn’t seem to support TIFF transparency)."

You need to use "save transparency."

How to decode tiff file and preserve opacity?

Tue, 07 Jul 2009 20:45:27 Z

Thanks a lot for reply, it's helpful information for me.
tnx