It sounds like you are comparing the before mosaic and after mosaic pixel values for the the same pixels, and the after mosaic values for the same pixels are much lower than the before mosaic values. Is that right? You didn't mention how you set the mosaicking paramters. The most common thing that I would expect to change the pixel values during mosaicking would be color correction. I assume that you turned off color correction by unchecking the Histogram Matching box under the Color Correction tab? If this doesn't explain what you are seeing, can you provide more information about how different the pixel values are, and what type of data you are mosaicking, and how you set the parameters? - Peg Exelis VIS

I think you are correct! I am concerned most with the data values rather than the colors, so I made sure it was unchecked. I may have introduced some error by layering all 7 bands and then mosaicking, which made it seem (it may have been the way I was querying in idl and ENVI) as if the values were far off. This time I am mosaicking each band first, then I will layer. I hope this fixes the issue. I intend to do an ISODATA and vegetation indices of the study area. I would like to compare results from ENVI to some IDL programming that I am working on. Thank you for the help and I appreciate any advice.

OK, so, after mosaicking, try displaying the original images and the mosaic, in different layers in the ENVI display. Then bring up the Cursor Value tool. It will show you the pixel values in all displayed bands for all displayed layers. Then you can see whether the pixel values were changed by the mosaicking process. - Peg