How rasters display in OrthoEngine is defined by raster representation.
Under Raster Representation, there are three lists in which you select the display properties to use when you open rasters in OrthoEngine.
In the Default resampling method list, you select how to resample the raster when viewing at greater than 1:1 resolution. The available options are as follows:
- Nearest neighbor is the most appropriate resampling method to use with discrete data. It identifies the gray level of the pixel closest to the specified input coordinates and assigns that value to the output coordinates. Although this method is considered the most efficient in computation time, it introduces small errors in the output image. The output image may be offset spatially by up to half a pixel, which may cause the image to have a jagged appearance.
- Bilinear interpolation determines the gray level from the weighted average of the nine closest pixels to the specified input coordinates and assigns that value to the output coordinates. This method generates an image with a smoother appearance than nearest neighbor, but the gray-level values are altered in the process, which can result in blurring or loss of image resolution. Similar to cubic-convolution resampling, bilinear interpolation is most appropriate for continuous data.
- Cubic convolution determines the gray level from the weighted average of the 16 pixels closest to the specified input coordinates and assigns that value to the output coordinates. The resulting image is slightly sharper than one produced with bilinear interpolation, and it does not have the disjointed appearance produced by nearest neighbor. Similar to bilinear interpolation, cubic convolution is most appropriate for continuous data.
In the Default visual enhancement list, you select the default visual enhancement to use with a newly opened raster. The available options are as folllows:
- None: Does not apply an enhancement to 8U data types. This setting does, however, apply a linear stretch or a linear enhancement to other data types using their pixel values. The stretch is applied using only those pixels displayed in the viewer. At a zoomed-out level, the pixel values are decimated before they are displayed in the viewer. Therefore, the range of pixels used for the linear stretch may be narrower than the actual range of pixels in the image file. This means that the actual minimum and maximum values in the image file may not be included in the calculation of the linear stretch. Tail Trim and Exclude Min/Max settings are ignored for all data types.
- Linear: Minimum and maximum values in the image are stretched uniformly over the entire range of the available output display to enhance the overall differences in gray levels in the image.
- Root: Compresses the range of higher values (brightness) and expands the range of lower values (darkness) so you can distinguish more detail in darker areas of an image while still retaining some detail in the brighter areas.
- Equalization: Distributes the values equally over the entire output display range, which results in a near-uniform histogram. This enhancement is effective in exposing details in the higher values (brightness) and lower values (darkness), but causes less contrast in the middle values.
- Adaptive: Combines the benefits of the Equalization and Linear enhancements, which results in a more natural display than Equalization, and compensates effectively for outliers.
- Infrequency: Assigns the values that occur least frequently in the image to the range of higher values (brightness) in the histogram so finer details become brighter.
In the Complex SAR interpretation list, you select how you want to visualize various interpretations of complex SAR data. You can load interpretations—for display only—without modifying the properties of the complex channel.
With a complex number, a + bi, where a corresponds to real part (I) and b to the imaginary part (Q).
The available options are as folllows:
- Intensity: Corresponds to I^2 + Q^2.
Intensity is also known as power.
- Amplitude: Corresponds to the square root of the intensity (I^2 + Q^2)^0.5
- Phase in radian: Corresponds to arctan (Q/I) in radian
- Phase in degrees: Corresponds to arctan (Q/I) in degrees
- Real: I
- Imaginary: Q
If you want to recompute the histogram using the pixels viewed currently each time the display changes, such as after panning or zooming, select the Auto re-enhance grayscale and RGB layers check box. If you want to use the histogram built when you selected the enhancement, and apply it to the display each time you pan or zoom, clear the check box.
Under Default RGB mapping, you can set up default mapping for all RGB data that you open.
To use the associated and valid metadata of the image file for the color channels, select the Use metadata (when present) check box. That is, when the file contains the metadata tags, DefaultRed, DefaultBlue, and DefaultGreen, OrthoEngine will use these to display the image. Otherwise, when there is no default RBG metadata in the file, OrthoEngine uses the values you type or select in the Red, Green, and Blue boxes, resepectively.