2003.01.24 20:50 "Re: Are there de facto defaults for resolution (TIFF 6 file) ??", by Michael O'Rourke
unfortunately some very odd folks put the resolution into a exif block in a tiff and not in the main tag table for a page. sucks, but in such circumstances you can only get the right into if you parse exif blocks too.
----- Original Message -----
I don't know if I'm running into readers and writers that are non-compliant, or whether there's a default of which I'm ignorant, but here's the issue. Maybe someone can clue me in??
The TIFF writer built into AutoCAD is locked at 100 dpi, according to its dialog box. Now that I'm delving into TIF file programming, I see that the resulting TIF file actually has no tags for Xres, Yres, or ResUnits. The latter has a default of INCHES, according to the TIFF 6 spec. However, the spec does not give defaults for the resolution tags. Also, the spec says the resolution tags are required for Baseline, bi-level TIFF files. My conclusion... ACAD's TIF writer is not Baseline-compliant. This would not surprise me too much...
The confusion, however, started when I use Windows Explorer to view the properties of the resulting TIF file. The X & Y resolutions were listed as 100 dpi. So, that would mean the Microsoft TIF reader is non-compliant, also, because it's assuming a default for non-existent resolution tags?
I can't find any other tags that MS Explorer could be using to deduce 100 dpi. The reason for this post is to make sure I don't add resolution tags that "contradict" other tags and result in an invalid TIF file. Also... I wanted to vent, because it would have been a lot easier for me to change existing (REQUIRED) resolution tags than have to add them. Also... You'd think MS could afford to spend a little time reading specs. :(