2007.01.17 02:25 "[Tiff] Elevation Data", by Craig Bruce

2007.01.17 18:03 "Re: [Tiff] Elevation Data", by Joris Van Damme


It seems to me Craig's data doesn't really have a photometric interpretation, since it isn't really an image. So he should just use something reasonable (min-is-black I would say), and use SampleFormat to indicate what the data really means.

I am confused about this. If we're talking about an ExtraSample, then clearly there is more freedom, but if the data is encoded in a main image color channel, covered by any photometric at all, we need to be consistent with the normal usage and the encoding that applies. Grayscale data, be it MinOrBlack or MinOrWhite, is grayscale data, and you may know it's elevation but if you write it as grayscale data, it's grayscale data. So the needs of renderers, and the encoding of grayscale, do come into play.

As for SMin/MaxSampleValue, Joris wrote:

If the spec were clear and binding on this, maybe things would have been different. But it isn't.

I don't see where the TIFF6 spec says they're just statistical. It doesn't specify sanctions for when they're wrong, but the text seems quite clear that if the tags are present, they are to contain the real bottom and top of the value range. An application rejecting a TIFF because it finds a sample value outside the defined range would be in its right based on the text.

You're absolutely correct. Ed pointed this out already. I was confusing my memory of Min/MaxSampleValue tags with SMin/SMaxSampleValue tags. I stand corrected.

So that leads me to think my proposal for a recommendation as specified in http://www.asmail.be/msg0055261416.html

  1. agrees with the spec
  2. agrees with needs like elevation encoding
  3. agrees with graphic rendering needs

Would you agree?

Best regards,

Joris Van Damme
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