2009 NAIP Image contrast difference

[JamesFitzgerald]

Hey

Need help!

The process is...I am creating a mosaic of three 2009 NAIP images for three counties within a watershed.  For each county the watershed has three parts (northern, central, and southern).For the NAIP images, I am extracting by mask with each separate part of the watershed, then I will do another extract by mask with the county and the northern watershed.  I will also do this same process with the central and southern portion of the watershed. This gives me an image of just the watershed and not the three counties.  The problem is with one of the images that I had extracted by mask. It is different in contrast.  The other two are fine.  How do I correct the contrast so it looks the same as the other images?  Is there a fix?

[RobertBerger]

Hi John,

the wavelet compression MG3 is very strong. So you can sometimes expect to have 1 GB file on disc that really have 50 or 100 GB of uncompressed data. The wavelet compression does not come with ArcGIS. You can buy the compression from a different company if you need it. Some compressions that come with ArcGIS are jpg or jpeg2000 that can also compress at a very nice ratio (play with the compression quality).
Note, when you compress data, you get rid of some quality (pixel variation) in the imagery for the sake of space. So every time you do something to the compressed data, and write out a new compressed dataset you loose more quality. Just something to be aware of.
Other compressions that are less strong but are loss-less (meaning you don't sacrifice quality for space) are LZW or LZ77. These compress maybe 3:1.
Look at this help topic for more information.
I hope this helps.

Robert