Image files are too large

[JerryBiedenbender]

Hello,

    I just received new aerial photography. I normally get it in .sid files that are reasonable in size and easy to work with. These new files are .TIFF files they are too large and they are giving me problems. Is there any way to convert .Tiff to .Sid files? or are there any other fixes for this problem?


Thanks,
Jerry

[RonaldBerger]

Jerry,

You can copy the tiff to a different high compression format, using the copy raster GP tool. To write to formats such as ECW and MrSID you'll need to get a license etc from the right company. ArcGIS does write jp2 compression out of the box which might do the trick for you. Also you could try jpg compression. Play with the compression quality for output size and quality.
If you needed somewhat less compressed imagery you could also try LZW in a GDB or Imagine Image format.
Let me know if this helps.

Robert

[JohnSobetzer]

Are your problems storing and moving such large files, or drawing them in ArcMap?

If it is storage space then you will certainly want to compress the tifs.  You might try LZW first.  It is lossless and doesn't affect draw performance much, but it also doesn't compress as much as others.  The problem with jpeg is that the whole file needs to be decompressed for use and it too doesn't have pyramids built in, so it can be slow.  The wavelet compression sids, ecws and jpeg2000s all have limits.  For any decent sized file you have to buy a sid compressor and it ain't cheap.  You might try Irfanview to compress to ecw if your input file is less than "500 MB".  You will then need to copy the world file (tfw) and rename it to eww.  If you have geotiffs you will need to use the world file creator to create the tfw before renaming it.  The jpeg2000 compressor in ArcMap produces a pretty slow performing version; there is a bug number for it.  The LizardTech jp2 compressor produces fast jp2s but it is also the sid compressor and hence expensive.  I'm not sure what happens with tifs stored in geodatabases - you might research that.

Tif files generally draw well in ArcMap, but they don't in themselves contain pyramid versions as sid images do which can improve performances at different scale.  If you are one option is to build pyramids.  Two other options are to clip the tifs to only the areas of interest you need, and/or break them up into smaller tiles and use only those you  need.

Finally, put them on your hard drive if they aren't already.  Networks are usually significantly slower and DVDs much slower.

[JerryBiedenbender]

What program do i need for converting to .LZW??

[JohnSobetzer]

If Irfanview can read your tifs, then it can convert them to tifs with the lzw compression.  It can work in batch.  Other programs like PhotoElements can also do the conversion.  If the tifs have a world file and a projection file then you are all set.  Just replace the old with the new.  But if it is a geotiff then you have to use the World File Creator (it will work in batch) to create a tfw for the new lzw tiffs.  ESRI's raster storage offers a variation of lzw in its storage environment (lz77) but then due to a bug it doesn't happen.  On some rasters, like topo drgs, lzw can achieve very high compression, even better than wavelet, and it is lossless.  On aerial photo rasters, however, it compression is much more modest, must less than wavelet.