Feature request: read TIFFTAGS from tif file.

[jcwright77]

I would like to load a tif file with vips and access tif tags such as those supported in TIFFGetField, eg TIFFTAG_SAMPLEFORMAT. I see a few of these are read in tif2vips.c but is there a way to access from vips when an tiff is loaded from file by vips? Basically a wrapper around TIFFGetField?

[jcupitt]

Hi @jcwright77,

It's one of the big limitations of libtiff -- it's not possible to write a function that can read or write an arbitrary TIFF tag. Instead, you have to switch on the tag number and write code for every case (this is how TIFFGetField works internally). This means we'd need to implement every tag by hand, which is far too much work.

You can see the fields which libvips does support with eg.:

$ vipsheader -a k2.tif
k2.tif: 1450x2048 uchar, 3 bands, srgb, tiffload
width: 1450
height: 2048
bands: 3
format: uchar
coding: none
interpretation: srgb
xoffset: 0
yoffset: 0
xres: 2.83465
yres: 2.83465
filename: k2.tif
vips-loader: tiffload
n-pages: 1
iptc-data: 84 bytes of binary data
resolution-unit: in
orientation: 1

It tries to support the fields which can be usefully interchanged with other format libraries.