3.7 Working with spectra
3.7 Working with spectra
When viewing an imagecube in the ImageCube view, you can display detailed information about any pixel of interest by selecting it. Clicking on a pixel in the ImageCube view (azimuth-elevation view only) selects the pixel and displays a Point of interest. The Point of interest appears as a yellow line that “skewers” the imagecube at the selected pixel.
|
When a Point of interest is selected, information about that pixel is displayed in the Downlink info pane:
- Position of the rover (in meters) in site coordinate frame and heading (in degrees) where the rover was located when the spectra were captured
- Image coordinates (labeled I,J) in the imagecube for the selected pixel
- Image ID of the imagecube being displayed
- Ick (instrument heartbeat) value when the pixel was captured
- Angle of the mast azimuth gimbal, in degrees (This angle is approximately 180 degrees offset from the Mini-TES pointing azimuth.)
- Angle of the Mini-TES elevation mirror, in degrees (0 is level, increasing toward zenith)
- Width and height of the spectral imagecube
- Number of bands of the spectral imagecube
3.7.1 Plotting a spectrum
A new window will appear that displays the spectrum plot. The title bar label displays the ID of the imagecube. The title of the graph indicates the spectral cube type (radiance, emissivity, brightness/temperature, or mineral map), the pixel line and sample, the Ick value, mast azimuth gimbal angle and elevation mirror angle. The horizontal axis is labeled in decreasing wavenumber and the vertical axis shows the pixel value.
3.7.2 Creating color composite images
The ImageCube lets you combine spectral cube bands to produce color composite images. There are two tools to help you do this: the Define Bands tool and the Define Band Range tool.
Define Bands
When an ImageCube view is first opened, you can see one band of the spectral cube at a time. With the Define Bands tool, you can create a color composite image from multiple bands (as in Figure 3.21). To use the Define Bands tool, select Define Bands from the Action menu. This will display the Define Bands dialog, as shown in Figure 3.22.
At the top of the dialog you see listed the list of available images in the view (mono_rad, mono_emiss, mono_temp). At the bottom there are the equation fields labeled Red, Green, and Blue. By default, these fields all contain the same equation (mono_rad[1]). Now we will show how you can enter you own equations to define an RGB composite image.
The format of the equations allows you specify arithmetic combinations of
image bands. You can define an arithmetic combination using the following
operators:
| + | Add together two image bands, such as mono[1] + mono[2], or an image band and a constant, such as mono[1]+42 |
| - | Subtract two image bands, such as mono[1] - mono[2], or an image band and a constant, such as mono[1] - 0.5 |
| * | Multiply two image bands, such as mono[1] * mono[2] or an image band and a constant, such as mono[1] * 1.25 |
| / | Divide two image bands, such as mono[1] / mono[2] or an image band by a constant |
| () | Group a set of operations parenthetically to specify a specific evaluation order, such as 0.3*(mono[1]+mono[2]+mono[3]) |
The image band terms that you combine with the operators are formatted according to
where imageName is one of the names of available images in the upper part of the Define Bands dialog, and bandNumber may range from 1 to the total number of bands in the image. (The number of bands in the image is given in the Downlink info pane.) Most of the time you may be interested in writing equations using only one particular image, but sometimes combinations of different images can be useful.
To see the result of your image composite equations, specify an equation for each of the red, green, and blue channels and click the Ok button. The image will recompute its appearance. In the ImageCube view, specifying an RGB composite image will move the image plane back to the front of the cube. If you drag the slider after you create a composite image, the composite image will be replaced with the image of the band you drag the slider to.
To return to the image to its original appearance, select an image from the Image menu or move the Index slider to revert the display.
Define Band Range
The second tool for creating color composite images is the Define Band Range dialog. This tool lets you quickly define red, green, and blue color components with menus and spinner controls. It is particularly useful for averaging a set of adjacent spectral bands and assigning the result to a color channel.
To use the Define Band Range dialog, select Define Band Range from the Action menu. The dialog is split into three panels from left to right, one for the red, green, and blue channel of the composite image (see Figure 3.23). At the top of each channel control panel you select the image to use. Next, for the selected image you set the minimum and maximum band index to use. If you set the minimum value to be the same as the maximum value, then only that band of the image will be assigned to that color. If you specify a range of bands (max ¿ min), then that color will be computed by averaging the brightness of all the bands in the range.
As you select the band ranges for each color channel, the ImageCube view display will automatically update to view the newly defined composite image as you work. When the image finally looks as you want it to, close the dialog or click the Dismiss button to continue working. To return to the image to its original appearance, select an image from the Image menu or move the Index slider to revert the display.
3.7.3 Stretching
3.7.4 Filtering
You can apply various filters to an imagecube to improve or enhance its appearance. The filters available in Maestro are median, high-pass, low-pass, Gaussian, and Sobel edge detection. To apply a filter to an image, select it from the Action-¿Filters menu or from the toolbar. You can apply any number of filters in any order you need to enhance an image. The Undo button lets you undo a filter if you aren’t happy with how it changed the image. For more information on filtering, see Section 3.4.3.
3.7.5 Exporting the image
The image that displayed in the ImageCube view can be exported as a JPEG image file. To export, select the Save Image menu item from the Action menu. A Save file chooser will be displayed, in which you can select the folder and enter the filename of the image file to export.
3.7.6 Image appearance
You can change the appearance of the image in the ImageCube view by selecting the interpolation options. The following interpolation options appear in the Action-¿Appearance menu:
- No interpolation: Each pixel is rendered in the view using only its own brightness. This results in a very coarse “pixellated” image.
- Bilinear interpolation: Each pixel is rendered in the view using a linear combination of its color and those of its neighbors, resulting in a smoother image.
Figure 3.24 shows an example of a spectral cube rendered with different appearance settings.
|
3.7.7 Displaying the image header
You can display the header of a PDS image in an Image view or ImageCube view by selecting the Show Header menu item in the Action menu. The header is displayed in a separate window (see Figure 3.25).
