## 2 Visualization of Hyperspectral Images  
A hyperspectral image is a collection of information derived from the electromagnetic spectrum of the observed area. Unlike the human eye that can only see visible light, _i.e._, the wavelengths between 380 and 760 nanometers (nm), the hyperspectral images reveal the frequencies of ultraviolet and infrared rays. Each material has an unambiguous fingerprint in the electromagnetic spectrum (spectral signatures). The spectral signature allows the identification of different types of materials. There is a wide range of real life applications where hyperspectral remote sensing plays a very important role. For example, in geological applications the ability of hyperspectral images to identify the various types of minerals makes them an ideal tool for oil and mining industries, and hyperspectral remote sensing is used to search for minerals and oil. Other important fields of application are ecology, surveillance, historical research, archeology, _etc_. The hyperspectral sensor for the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) [8] format measures the spectrum from an area of 400 up to 2500 nm, with a nominal 10 nm sampling. This generates 224 narrows spectral bands. The resulting hyperspectral data allows an analysis of the composition of materials by using spectrographic analysis that defines how materials react to solar radiation. The AVIRIS system measures and records the power level of the radiance of the instrument. In the rest of this paper we have tested our approach on six hyperspectral images provided freely by NASA JPL: _Cuprite_, _Lunar Lake_, _Moffett Field_, _Jasper Ridge_, _Low Altitude_ and _Yellowstone_. The _Cuprite_ hyperspectral image was collected from the site of Cuprite mining district, located in Nevada (USA). _Lunar Lake_ was acquired from the site of the Lunar Lake in Nye County, Nevada, USA. _Moffett Field_ was captured from Moffett Federal Airfield ([9]), a civil-military airport in California (USA) between Mountain View and Sunnyvale. The _Jasper Ridge_ hyperspectral image covers a portion of the Jasper Ridge Biological Preserve ([10]), located in California (USA). The _Low Altitude_ hyperspectral image was recorded by using high spatial resolution, in which each pixel cover an area of 4 \(\times\)4 meters, instead of the 20 \(\times\)20 meter area recorded by the other images. The hyperspectral image denoted as _Yellowstone_ covers a portion of the Yellowstone National Park ([11]), located in USA. We have implemented a tool to visualize single bands of a hyperspectral image or to visualize the combination of three bands. For the visualization of a single band, each signal level is converted to a grayscale tone. Therefore, the resulting image is a grayscale bitmap ([12]). In the second case, our tool permits the selection of three bands, and each band is assigned to a RGB component. The resulting image is a false-color visualization, where each signal level of the first band is converted to the red component, the second band is converted to the green component and the last one is converted to the blue component. The bands can be assigned to the RGB components according to their wavelength into a spectrum (as proposed in [13]). For example, the spectral band of the red color (wavelength from 620 nm to 750 nm) is assigned to the red component of the RGB, the spectral band of the green color (wavelength from 495 nm to570 nm) is assigned to the green component of the RGB and the spectral band of the blue color (wavelength from 450 nm to 475 nm) is assigned to the blue component of the RGB. Figure 2 shows the visualization of band 120 of the AVIRIS image Lunar Lake (Scene 01). Figures 3 and 4 show respectively a false colors visualization of the AVIRIS images Lunar Lake Scene 03 and Yellowstone Calibrated Scene 11. The resulting images are generated by assigning band 125 to the red, band 70 to the green and band 30 to the blue.