Eduardo Perez ([EMAIL PROTECTED]) wrote:
> Performing 'linear' operations on an image (such as color correction) is
> not much slower on the tiled architecture. But 'non-linear' access to
> the image (such as 90 degree rotations) is terribly slow when the image
> has been swapped out. As far as you read the data on the same order it
> was stored (row order, usually), the disk heads will not have to move
> too much, because you are reading data from adjacent positions. But if
> you try to read the data in another order (column order, on the 90
> degree rotation example), the heads of the disk must go forward and
> backwards to find the data. Storing the data using a tiled order solves
> this probblem, as you can read a whole tile into memory each time.

You can always read in the linear file in row order (and write the
results in column order to memory in the case of 90 degree rotation).
This will go at full disk speed. 

The main uses of the tile system, as far as I can see it, is for
undo's, and for the case that if you have one huge image that doesn't
fit into memory and you're going to change small portions of it (like

Btw, for the storing of undo data to disk, the Gimp is doing it at a
fraction of full disk speed.

  --  Ewald

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