Using Arc 10.0, I have a single band, 32-bit signed raster as the only item in a file geodatabase. Using ArcCatalog, I copy that raster to a new geodatabase with an 8-bit unsigned pixel type. As expected, Raster Properties shows that the 8-bit raster is smaller (438 MB) than the 32-bit raster (1.71 GB). However, when I measure the size of the two gdb folders using Windows File Explorer properties, the 32-bit folder is smaller(!) than the 8-bit folder (64 vs 83 MB, respectively). Both gdb folders contain 66 files.
Both rasters are 32,225 X 13,417, single band, 30 meter cell size, FGDBR format, continuous Source Type, no colormap or pyramids, with LZ77 compression. The only difference is the pixel depth and type: 32-bit signed integer vs 8-bit unsigned integer.
Why is the 32-bit gdb folder smaller than the 8-bit folder, as measured by Windows File Explorer? Why does Arc raster properties report such wildly inflated size (438 and 1,710 MB) compared to Window File Explorer (83 MB and 64 MB)?
In ArcMap, the 32-bit image takes about 9 seconds to display, while the 8-bit image loads almost instantly.