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POWPF BitmapImage and TIFF with CMYK + Alpha
 

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  1. POWPF BitmapImage and TIFF with CMYK + Alpha
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    <p>I am using this code snippet to load various image files:</p> <pre><code>BitmapImage bitmap = new BitmapImage (); bitmap.BeginInit (); bitmap.UriSource = new System.Uri (path); bitmap.CreateOptions = BitmapCreateOptions.PreservePixelFormat; bitmap.EndInit (); </code></pre> <p>This works fine for TIFF files stored as RGB, RGB+Alpha and CMYK. <strike>However, if I try to load a TIFF file using CMYK colors and an alpha channel, I get an exception (the file format is not recognized as being valid by the decoder).</strike></p> <p>I was previously using the <a href="http://freeimage.sourceforge.net/" rel="nofollow">FreeImage</a> library and a thin C# wrapper on top of it. FreeImage 3.x has partial support for this kind of image format, i.e. I had to load the TIFF twice, once as CMYK without transparency and once as RGB+Alpha; this trick is needed since FreeImage only gives access to at most 4 simultaneous color channels.</p> <p><strike>I'd like to know if there is a supported way to load CMYK+Alpha bitmaps? Either directly in C# or by going through some interop code, but preferably without having to use a third-party DLL (other than the .NET 4 framework libraries).</strike></p> <p>An example of such a TIFF file can be found <a href="http://www.opac.ch/files/cmyka.tif" rel="nofollow">here</a>.</p> <p><strong>EDIT</strong> : I can no longer reproduce the problem, the following code works just fine:</p> <pre><code>BitmapImage bitmap = new BitmapImage (); bitmap.BeginInit (); bitmap.UriSource = new System.Uri (path); bitmap.CreateOptions = BitmapCreateOptions.PreservePixelFormat; bitmap.EndInit (); byte[] pixels = new byte[bitmap.PixelHeight*bitmap.PixelWidth*5]; bitmap.CopyPixels (pixels, bitmap.PixelWidth * 5, 0); </code></pre> <p>But I am still stuck: how can I find out that the source image was encoded as CMYK plus Alpha channel? When looking at the <code>Format</code> property, I get only the information that the image has 40 bits per pixel. All the interesting stuff is stored in the following non-public properties:</p> <pre><code>bitmap.Format.FormatFlags == IsCMYK | NChannelAlpha; bitmap.Format.HasAlpha == true; </code></pre> <p>Is there any official way of getting to them, without resorting to reflection?</p>
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    1. USPierre Arnaud
    1. USPierre Arnaud
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    1. CODo you have any link to a TIFF using CMYK with alpha channel where this problem occurs? I'm unable to reproduce this
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      1. USFredrik Hedblad
    2. COI added a link to my TIFF image in the question (http://www.opac.ch/files/cmyka.tif)
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      1. USPierre Arnaud
    3. COAh, you're right. Sorry, totally missed it..
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      1. USFredrik Hedblad
 

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