I wrote some articles a few years ago about how to combine Landsat RGB band file data into color images using low cost utilities like Paint shop Pro. Although this worked OK, the general image processing utilities were not exactly what was needed for this application. In addition, general-purpose image processing programs like Paint shop Pro and Photoshop are not capable of pan sharpening images. Pan sharpening is the process whereby lower resolution color data is combined with higher resolution panchromatic data to produce higher resolution color images.

PANCROMA is a powerful new utility for creating such pseudo true color RGB images and pan sharpened images from Landsat and SPOT satellite band files. The program is designed to complement free Landsat databases such as the University of Maryland Global Land Cover Facility (GLCF) database. Landsat data is available from other sources as well, and PANCROMA can handle most of the common formats that you will encounter.

Landsat data files are very large. Each of the three band files needed for pan sharpening is about 60MB in size. The panchromatic file is even larger: about 250MB. Several temporary files of similar size are required to perform the necessary transformations. As a result, pan sharpening uses a lot of computer resources and more powerful computer is preferred for the compute-intensive algorithms required especially for pan sharpening.

The primary purpose of the Landsat survey satellites is to provide scientists with data to assess the earth's vegetation, crop and mineral resources. It was not designed to produce true color images of the earth's surface. However, Landsat bands 3, 2, and 1 are close to the red, green and blue (respectively) wavelengths that the human eye is sensitive too. These bands can be inserted into an RGB color model and will produce images that are very satisfactory for visualization. Scientists often combine other Landsat bands in order to produce false-color images for other purposes. For example, bands 4, 3, 2 are commonly used to highlight vegetation. Many other combinations of bands are used for different purposes.

The latest Landsat sensor is the Enhanced Thematic Mapper (plus) (ETM+). Among other improvements, ETM+ included for the first time a 15m resolution panchromatic band. Rather than detecting radiation in a narrow range of frequencies, a panchromatic sensor collects radiated energy across a broader spectrum. And it does so at increased resolution compared to previous sensors, i.e. 15m/pixel as opposed to the 30m/pixel resolution of the band sensors. The panchromatic data is not recorded in separate RGB channels but instead is recorded in a single channel. So despite having greatly increased resolution compared to bands 1-7, the panchromatic band can only be displayed as a black and white image. The corresponding visible RGB color data is stored separately in channels 3, 2, and 1, but at a lower (30m) resolution. Looked at another way, each band channel contains only 25% of the pixels and visual information of the panchromatic channel. If there were a way to combine the color information in these channels with the higher resolution image information in the panchromatic channel then it would be possible to produce color images at the higher (15m) resolution. This is precisely what the PANCROMA algorithms do: produce 15m color image that can look as natural as the lower resolution images produced by combining the band data. Because Landsat covers virtually the entire earth, you can produce such images for any area that interests you. Unlike image data extracted from sources such as Google Earth™, Landsat is copyright free.

A lot of data is recorded in each Landsat scene. As a result, Landsat files are the largest that most people will ever encounter in any context. ETM+ band files are approximately 60MB each, and you will need three of them for pan sharpening. The ETM+ panchromatic (PAN) file is around 250MB. Fortunately you only need one of these at a time. The size of these files introduces challenges for the user and even greater challenges for the programmer.

PANCROMA can provide the following satellite image processing features:

• Display individual grayscale band files at full resolution

• Create 30m resolution pseudo true-color RGB images from Landsat or SPOT band files 3, 2, 1 instantly

• Create 30m resolution false-color images from any combination of Landsat or SPOT band files

• Create 15m resolution pan-sharpened images from Landsat ETM+ or SPOT band files and panchromatic band data using HSI or Brovey Transform methods

• An extensive set of custom image processing tools and utilities for superior image results

• Automatic subsetting of Landsat file sets to a matched sets of band and panchromatic files for subsequent pan sharpening

• Resampling of large Landsat files to lower resolution

• Batch processing of RGB band files

• Gap fill utilities for ETM+ SLC-Off images

• Sample image and compute pixel running average for better gap fill results.

• Import Landsat or SPOT files in .tif, .L1G, .jpg and .bmp format

• Save processed files in .jpg and .bmp format

A great deal more information is provided in the PANCROMA Instruction Manual that you can download from www.PANCROMA.com. A free trial version of the software is also available for download as well.