Problems compressing .sid file

Ice Age MarkIce Age Mark Global Mapper UserPosts: 324Trusted User
edited January 2012 in Raster Data
Hello Mike,

I have a 1.7GB county NAIP (.sid) image and I'm trying to export a (+/- 80%) rectangular area to use on a laptop with live GPS tracking in the field. While this is still a somewhat large file at FULL (1m) resolution (+/- 1.3GB), I can't seem to further reduce the file size with any kind of compression in the Geotiff or the GMP options. The GMP raster option says it's too large for JPEG compression. With Geotiff I've tried LZW and JPEG compression, but the file size is already larger than 1.3GB when the export is only about 20% complete. Also, I tried "No Compression", and the export time was actually a little shorter that with LZW or JPEG compression. Even stranger, during one attempt I forgot to crop to my polygon and exported the whole county image, and the file size was 14GB! This export only took about 1 hour, but the cropped LZW export took about 1.5 hours.

Is a .sid file so compressed that other types of compressions actually make the file much larger upon exporting? Previously (V12 2009 imagery), I was able to get a similar sized area/file size down to about 350MB for my laptop with Geotiff LZW. I'm not understanding any of this, or what I could be doing wrong. Any help or insight would be appreciated.



[V13 B011912]


  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2012

    Yes, the SID compression for imagery is about as good as it gets, with ECW and JPEG2000 being comparable. For imagery LZW is not nearly as good as it is lossless so it can't do nearly as good as a lossy wavelet-based format like SID/ECW/JPG2000. For scanned maps with a limited set of colors LZW might do better as that's not really what the wavelet ones are designed for, but for NAIP imagery you really aren't gonna get much smaller than what you started with without reducing the resolution or using ECW or JPEG2000 with a high target compression ratio.

    Let me know if I can be of further assistance.


    Global Mapper Guru
  • Ice Age MarkIce Age Mark Global Mapper User Posts: 324Trusted User
    edited January 2012

    I understand now, though it's not what I wanted to hear. I'll go for smaller areas and/or lower resolution, depending on the use circumstances. Thanks much for the quick answer.

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