1994.04.22 13:10 "Re: TIFF Tags for remote-sensing", by Francois Gauthier
I was wondering if there has been any work regarding the use of TIFF to store multispectral data sets. Most TIFF implementations place severe (for MS data) restrictions on the number of samples per pixel (bands) usually 3 or 4. This is completely inadequate for remote-sensing.
In principle there is no restriction on the number of samples in a TIFF image. All the samples must have the same resolution, though. (I seem to recall that the far infrared band of Landsat only has half the resolution of the rest)
The main problem is that there is no suitable value for the photometric interpretaion tag. I suggest that you contact Aldus and request that a new value "Multispectral" is included in the next version. Alternatively, you may want a private value. The tag has no default value, nor is it a "required" field, thus you may simply omit it. This is "right" in the sense, that multispectral data have no real colors per se, only when you assign colors to the bands, the picture comes out in (false) colors.
P.S. (just speculating) New values of the resolution unit tag may be also beneficial to remote sensing applications, including pixels per meter and pixels per kilometer. You may also want new tags for describing the geographical area depicted, wavelenght intervals for each sample,...
A perhaps simpler alternative would be to use a subimage for each or for smaller subsets of spectral bands.
This approach would enable the TIFF reader to read spectral bands selectively. This is usually more efficient unless your application requires that all spectral information be in core memory at all times. If so, then it makes no difference how the image(s) is/are stored in the TIFF file.
Since subimages can have different resolution (they have separate directories), this should be ideal for Landsat images.
The only inconvenience is that TIFF readers such as xv can only read the first subimage. Getting access to the other subimages is not difficult and may eventually be supported in later releases of xv. I must caution though that I have absolutely no knowledge of this happening anytime soon.
Hope this helps
Francois Gauthier (514) 928-4600 Ext.: 599
M3i Systems, Longueuil Quebec
e-mail: email@example.com or firstname.lastname@example.org
Disclaimer: All opinions my own.