2002.05.13 21:36 "Re: Fwd: Re: tsmAPI and LibTIFF", by
They definitely don't do this right. The TIFF orientation is for the image as a whole. It is NOT strip or tile specific. If it was, then this concept would also apply to multi-strip images (!) and we would need strip/tile specific processing.
"JPEG assumes a top-left origin and so any TIFF viewer will flip each tile"
This is not correct thinking. This statement applies to a JFIF image as a whole. We must not apply this thinking on partial ("raw") JPEG data.
Note that the statement also implies that the image is always stored consequtivelty from row 0 to row N. This part of the statement is true and is also quite relevant for strip/tile storage! Unfortunately, their implementation does not follow this. They have implemented an ordering where the rows no longer appear consequtivelty (4321|8765|...). The row and column order ordering for strips and tiles should always be (1234|5678|...) or (...|8765|4321).
Think of it like this: The TIFF data stream defines a two dimensional image [0..X, 0..Y]. The TIFF orientation only tells where the origin [0,0] is placed! That's all it does. It should not cause any inter-strip or inter- tile changes.
Here is their answer. Any comments?
>X-Authentication-Warning: Lomond.AI.SRI.COM: reddy owned process doing
>>-bs Date: Mon, 13 May 2002 13:02:25 -0700
>From: Martin Reddy <reddy@AI.SRI.COM>
>To: "Antonio E. Scuri" <email@example.com>
>Subject: Re: tsmAPI and LibTIFF
>Organization: SRI International - Artificial Intelligence Center
>In the tsmApi, we use a left->right, bottom->top ordering of pixels
>>which is common in geospatial applications, i.e. the origin is in the >>bottom-left corner not the top-left corner. We correctly set the TIFF
>>flags that specify this so any reader that supports TIFF fully will be >>able to view the raw (uncompressed) tiled files and flip them
>>correctly. However, an issue does arise when using JPEG compression for >>the data in each tile. JPEG assumes a top-left origin and so any TIFF
>>viewer will flip each tile. Because we use TIFF as a storage format for >>our own terrain data, this is not a big concern for us and the data is
>>read back correctly by the tsmApi library anyway (and ultimately by our >>TerraVision terrain visualization system).
>On Mon, 13 May 2002, Antonio E. Scuri wrote:
> > Martin,
> > I noticed that you use the LibTIFF for reading the TIFF images.
> > I don't know if you guys are aware of a discussion going on in
>> > the
> > LibTIFF news about the image tiles used by the tsmAPI. In
> > http://www.libtiff.org) Check for the "Orientation and Tiled
> > or go direct to: images?" thread
> > The images seem to have the tiles in a reversed order.
> > Best,
> > scuri
>Martin Reddy SRI International, AI
>> Menlo Park, CA
>firstname.lastname@example.org Tel : (650) 859-6468
>http://www.martinreddy.net/ Fax : (650) 859-3735