j wrote:
"Barry Pearson" wrote:
DNG does NOT support layers! (Not on the current version). But it is indeed based on TIFF, and it supports XMP metadata.
Thanks for that, Barry. TIFF supports layers, so I thought that DNG would, too.
It is worth noting that DNG comes in 2 "flavours": call them Raw DNG and Linear DNG.
Raw DNG, (the default, and typically what people mean when they say "DNG"), holds raw image data. It is a "common raw file format".
Linear DNG holds demosaiced image data. But … there is little difference between "demosaiced" and "never mosaiced". Lightroom can open a TIFF or a JPEG and save it as Linear DNG. And, of course, TIFFs and JPEGs don’t even have to have come from a camera. So products, such as ACR, Lightroom,Silkypix, etc, that support Linear DNG may be handling data that didn’t come from a camera!
http://www.barry.pearson.name/articles/dng/linear.htm I have been waiting for someone, Adobe or someone else, to provide a "file format" plugin for Photoshop that would enable "any" (?) image open in Photoshop to be saved as Linear DNG. There would be restrictions, and it might be like some of the other "save as" options, with a dialogue about what to do to save it. ("Flatten layers?" Etc).
I am not ruling out the possibility that Linear DNG could be extended to support layers. Perhaps it would "simply" mean being able to hold lots of "Main image" IFDs, allowing extra "Samples per pixel" for a layer mask and alpha channels, and some extra tags for layer adjustments. (I’m sure that is over-simplified! I don’t actually know how TIFF supports layers).
All I am saying is that this is not in the current DNG specification version. But, as you say, it is based on TIFF, so copying features from TIFF into the specification may be "easy" to do. At the moment, if you open even a Linear DNG file in Photoshop, it invoked the ACR plugin, and treats it like a raw file, and ACR doesn’t support layers. But these are hardly beyond Adobe’s abilities to resolve if they have cause to.
I hope to be surprised with what can be done with DNG in CS3! But Adobe needs to pursue "metadata editing" fast because Aperture, NX, LightZone, and others are doing so. I doubt if they would let "pixel rendering" developments interfere with that.
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Barry Pearson
http://www.barry.pearson.name/photography/