Most of you are probably already using GeoExpress 7. We’ve received some rave reviews from some of you about the new features we added, so we thought this might be a good time to introduce and explain how to use some of the great new tools in GeoExpress 7.
If you’ve ever received imagery from the USDA NAIP program, particularly MrSID Generation 2 (MG2) images from previous years, you’ll have noticed that many of the images have black collars around them. If you load these images into your GIS application and drop out these black collars, you’ll see a lot of ugly “speckling.”
These speckling artifacts happen because compressing images to MrSID at high compression ratios requires approximating colors. In other words, “black” becomes “almost black.” While the human eye doesn’t ordinarily notice the difference, this can make it difficult, not to mention ugly, to mosaic images together. Speckling happens with other background colors, too. Below you can see speckling around the edge of a mosaic with a white background.
Not to fear, though. GeoExpress 7 has new “despeckling” tools to clean these images up.
Start GeoExpress, and add your SID files to the “Despeckle” tab of the job list. In most cases, you won’t even need to adjust any options (however, note that despeckling is not available for MG2, so if you want to despeckle your MG2 imagery you’ll need to encode it to MG3 or JP2). Just click the “Despeckle Selected Images” button below the job list and GeoExpress will clean up your images for you. Here’s the result:
Next time, we’ll talk about “tiling out” images as TIFFs.
Images courtesy of MapMart.
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