1-bit raster datasets

When a raster can only store values of 0 or 1, it has a bit depth of 1. For each pixel of the raster, a corresponding bit can either be stored in the off position (0) or in the on position (1). One of the most common formats for 1-bit raster data is TIFF. Often these rasters are very large and are compressed using various techniques (CCITT Group 3 1-D, CCITT Group 4, Packbits, LZW, or None).

To increase the display speed when viewing 1-bit data, you may want to consider building pyramids. Typically, 8-bit pyramids are built using a technique of scaling the black-and-white values to 256 shades of gray (between 0 and 1). It is recommended that you build the pyramids using the bilinear interpolation resampling method.

When storing 1-bit raster data in a file or ArcSDE geodatabase, it is recommended that you choose the option to convert the 1-bit data to 8-bit. In this conversion, the value 1 in the input raster dataset will be changed to 255 in the output raster dataset. One-bit raster datasets have 8-bit pyramid layers when stored in a file system, but in ArcSDE or a file geodatabase, 1-bit raster datasets can only have 1-bit pyramid layers, which makes the display unappealing. By converting the data to 8-bit in ArcSDE, the pyramid layers are built as 8-bit instead of 1-bit, resulting in a proper raster dataset in the display.

Because 8-bit pyramids might be present, 1-bit TIFFs are always assigned to the Stretched renderer rather than the Unique Values renderer.

To facilitate fast access and display of 1-bit TIFFs, they are decompressed into memory when they are added to ArcMap or previewed in ArcCatalog. This is efficient but can require a larger amount of RAM or virtual memory if you need to display numerous large 1-bit rasters simultaneously. CCITT-compressed rasters have compression ratios of 100:1 or more. To display three of these rasters, each with a size of 1 MB and compressed at 100:1, you will need 300 MB of combined RAM and virtual memory. If a raster draws as all black, you could have exceeded your current memory allotment. If necessary, increase your virtual memory to allow hard disk space to be used like RAM. This can be set in your computer's system properties.

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