On Fri, 13 Jun 2008, Mitesh wrote: > I am a newbie in color management. > > I followed the "tifficc" sample project. > > I am using sRGB Stock Profile as the output profile. > > I have an RGBA8 (32-bit) tiff files. But this sample project transforms the > files into RGB8 (24-bit) tiff files without the alpha channel. > > I want to preserve alpha channel in the transformed tiff files. How can I > make this happen?
Tifficc is best described as a technology demo or test tool. TIFF is a complex format. If TIFF is important to you, then you should consider using other software. I am fairly sure that the free software I maintain (GraphicsMagick) does preserve the alpha channel, and it is far more comprehensive at supporting TIFF. Alpha channels and CMS are an interesting topic since quite often the image was intended to always be alpha composited on top of some other image (e.g. a solid color background) so the final colors are not the same as the RGB channels would suggest. Alpha in TIFF is normally the pre-multiplied type so the RGB channels do not represent the "actual" color. The RGB channels appear as if the image was alpha composited on top of a black image. Before performing a CMS transform, it is necessary to "disassociate" the alpha but this is not necessarily entirely successful since some color information may still be associated with the alpha channel based on the assumption that the image will normally be composited on some other color (e.g. white or black). GraphicsMagick does convert from pre-multiplied alpha to the "disassociated" alpha it uses internally, but it is not clear if all images will behave the same. Behavior depends on how the generating software used the alpha. For example, an image in the libtiff sample image collection uses the alpha channel to draw text on the image and the text information is mostly in the alpha channel. Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
