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Does anyone have experience subsetting/clipping a large NAIP imagery file in MrSID format? Some of the NAIP files we have are by county and they have really large file sizes.

The files are from the FSA NAIP Imagery.

How does it work if you subset a MrSID file? Does ArcGIS has to uncompress it first before it can proceed to clip or subset an area of interest?

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It's not completely clear what you're asking here. Do you want to know whether clipping a MrSID file can be done efficiently within ArcGIS? Are you asking about the mechanics of doing it? (I edited out your line about having experience with these files because it was self-contradictory, but I take it you have a working knowledge of using MrSID files in ArcGIS.) –  whuber Nov 16 '11 at 4:28
    
Every time you clip a raster, you're creating a completely new raster. To even display it, ArcGIS and any other software capable of reading MrSID files has to decode the file, and then to create a new raster, re-encode it back into the MrSID format. This should be effectively transparent to you, the end user. –  blah238 Nov 16 '11 at 4:42
    
@blah The interesting thing about MrSID is that it supports selective decoding, which suggests the possibility of decompressing blocks or at smaller scales with much greater efficiency than a full decompression. Thus it seems there is a genuine question here. –  whuber Nov 16 '11 at 4:47
    
Thank you everyone for replying. –  PROBERT Nov 16 '11 at 15:27
    
The best way to do is to use selected graphics in ArcMap and the export the output file as a Imagine file. Then Open in ERDAS and do the mosaic. This works very well for me. It keeps the same color as I had the original naip file. –  PROBERT Dec 2 '11 at 16:36

1 Answer 1

The short answer is you can't produce a clipped sid image in ArcGIS 10, the format is proprietary. But you should be able to produce a clipped jpeg 2000 (jp2) which is similar. A typical sid compression is 20 to 1. In ArcGIS to get the equivalent compression on a jp2 you would use 5 in the Environment - Raster Storage form compression quality box. (That setting has always been counterintuitive to me. You get it by dividing 100 by 20.) You need to use jp2 as your extension in the output raster dataset and you need to select jpeg2000 in the environment -raster storage compression drop down. Uncheck build pyramids, the format does that already. If you still have trouble clipping a sid to a jp2, you might first convert the sid to jp2, then clip that. Note if your sid image is in the newest sid format (MG4) you may need to download a plugin from LizardTech to handle it.

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