1994.10.24 15:34 "Re: Pipeable Tiff and Colormaps", by Sam Leffler
Pipeable TIFF -
I am looking for the ability to generate "pipeable" tiff stream files. Does anyone know of any effort going on in this area? I envision "pipeable" tiff files as having all non-image data fields prior to image data fields. That way when the image data is read from the stream, one knows how to interpret it without loading the entire image into memory. With such files, utilities can be piped together to process imagery concurrently.
I know of nothing going on related to my software.
The TIFF 6.0 specification requires colormaps for palette files, but does not specifically exclude them for other photometric interpretations. Also Sam Leffler's fabulous software allows ( at least version 2.4 allows ) colormaps for grayscale images.
I'm not sure what you mean by "allows colormaps for grayscale images", except that the software doesn't complain if a Colormap tag is present in an non-Palette image. I suppose it could since the Photometric tag sorts before the Colormap tag.
My questions are:
- Are colormaps valid for grayscale files and files of other photometric interpretations? If so, is the scanline indexes into the colormaps as it is for palette files? Why don't such files have a photometric interpretation of palette?
I believe that the Colormap tag should be interpreted only when the Photometric is Palette. (I don't recall the language in the spec, or if there's even any language that addresses this.) I'm pretty sure this is the "intent of the spec".
- Do people actually use such files or are they simply obsolete forms of TIFF files.
If you've found a vendor that generates TIFF that has Photometric other than Palette and a Colormap tag, and the colormap is needed to properly make use of the image data then the vendor is writing something that will not be very portable.