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May 2002
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2002.05.09 16:10 "Re: Orientation and Tiled images?", by Peter Nielsen
> In looking at a tiled image I have with orientation of 4, it seems that > the orientation should be used to determine the order of the tiles but > the data within the tiles is still Y to Y+N. For instance the first > tile is the bottom of the image, but the raster lines are from 1100 to > 1300, not 1300 to 1100. > > Is this normal and correct? AFAIK the orientation is just a "display" tag. It tells how to render the image. It does not tell how to store internal TIFF data. The main purpose of the orientation tag is to let devices (e.g. cameras) store the image with the captured rotation and thus avoid additional (and possibly prohibitive) processing overhead at the time the TIFF is created. The image should render correctly even when ignoring the orientation tag. Thus, the internal TIFF row ordering within tiles must not depend on the orientation tag. Consider this: -Read TIFF and ignore the orientation tag -Check orientation tag -Rotate image if orientation tag tells to This should always work correctly. If it does not, something is wrong. > In looking at a tiled image I have with orientation of 4, it seems that > the orientation should be used to determine the order of the tiles but > the data within the tiles is still Y to Y+N. For instance the first > tile is the bottom of the image, but the raster lines are from 1100 to > 1300, not 1300 to 1100. > > Is this normal and correct? Assuming that I correctly understand what you're saying: No, this is not correct. In a tiled 200x200 tile image, tile 1 will contain rows 1 to 200. Now, if you render this Wx1300 image upside down (orientation = 4), then the first tile will correspond to rows 1300 to 1100 on screen, starting with row 1 in tile 1 corresponding to row 1300 on screen. Best regards, Peter Nielsen http://www.pmview.com