[Gdal-dev] XResolution / YResolution tags

[Andrey Kiselev]

On Thu, Jul 28, 2005 at 12:53:25AM +0200, G?rald CLETTE wrote:
> I've found in the TIFF specification Rev 6.0 that the X/YResolution
> tags don't have any default value. It's also written that these tags
> are required for Bilevel Images, Grayscale images, Palette color
> images as well as for RGB images. I noticed that applications can
> display the images  with no care (!) with these tags but it's not
> written that these tags can be absent.
>  
> I'm just trying to find how to get a default value for these tags (if
> any but I don'tthink that it's a good idea to fx one) or a way to
> calculate it.


Gerald,


The resolution tags do not required to display an image and most image
viewers just ignore these tags. Displayed image can be arbitrary scaled
and we do not need predefined resolution, because it can be changed
dynamically. Resolution tags specified in the TIFF spec as required
fields, but you can safely omit them and vast majority of software will
open your files without problems. There is no default value for
resolution, but if you want to add the one for your files you can use
something like the 72 dpi or 100 dpi (typical display resolution).

Best regards,
Andrey


-- 
Andrey V. Kiselev
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