2010.04.01 21:52 "Re: [Tiff] TIFFReadScanline and large compressed one-strip files", by Chris Cox

Tom;

Compression ratios improve if you use larger strip sizes.

And on modern machines, 290 Meg is next to nothing.

(some video/3D software likes to write TIFF files as a single tile/strip)

So I can see how such an image might get created.

But LifTIFF should be able to read sub sections of the strip when memory is limited (say, on embedded devices). (Photoshop reads subsections as memory allows, down to a single row at a time, regardless of the strip size)

Chris

On 4/1/10 2:30 PM, "Tom Lane" <tgl@sss.pgh.pa.us> wrote:

I have an LZW compressed TIFF file of 290MB or so with the whole image in one strip. Reading the file with the TIFFReadScanline() function causes the entire 280MB of compressed data to be loaded into memory at the point the first scanline is read.

My client is finding that in some cases on 32bit systems there isn't 290MB of contiguous memory available and would like a way avoiding prereading the whole strip.

Does anyone have any suggestions for this?

Whack the file's producer upside the head? The entire *point* of the strip/tile mechanism is to limit the amount of data that has to be slurped in at once. I can't see why libtiff should be expected to go to enormous lengths to work around such blind misuse of the format.