PC Spectral Sharpening

Use PC Spectral Sharpening to sharpen a low spatial resolution multi-band image using an associated high spatial resolution panchromatic band. The algorithm assumes that the low spatial resolution spectral bands correspond to the high spatial resolution panchromatic band. If both data sets are georeferenced, ENVI additionally co-registers them on the fly.

You can also write a script to perform PC spectral sharpening using the PCPanSharpening task.

See the following sections:

Background

ENVI applies Principal Components (PC) spectral sharpening by:

  1. Performing a PC transformation on the multispectral data.
  2. Replacing PC band 1 with the high resolution band and scaling the high resolution band to match the PC band 1, so no distortion of the spectral information occurs. The PC spectral sharpening method assumes that the first PC band is a good estimate of the panchromatic data.
  3. Performing an inverse transform.
  4. Resampling the multispectral data to the high resolution pixel size using a nearest neighbor, bilinear, or cubic convolution technique.

Run the PC Spectral Sharpening Tool

The images must be georeferenced or have the same image dimensions. If the images are georeferenced, ENVI co-register the images before performing the sharpening.

To apply PC spectral sharpening:

  1. From the Toolbox, select Image Sharpening > PC Spectral Sharpening. The Principal Components Pan Sharpening dialog appears.
  2. In the Input Low Resolution Raster field, select a low spatial resolution multispectral input file. Perform optional spatial and spectral subsetting, and/or masking, then click OK.
  3. In the Input High Resolution Raster field, select a high-resolution input image. Perform any optional spatial subsetting, then click OK.
  4. Select the resampling method from the Resampling drop-down list. The choices are:
    • Bilinear (default): Performs a linear interpolation using four pixels to resample
    • Nearest Neighbor: Uses the nearest pixel without any interpolation
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
  5. Enter a filename and location for the Output Raster.
  6. Enable the Preview check box to see a preview of the settings before you click OK to process the data. The preview is calculated only on the area in the view and uses the resolution level at which you are viewing the image. See Preview for details on the results. To preview a different area in your image, pan and zoom to the area of interest and re-enable the Preview option.
  7. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  8. To reuse these task settings in future ENVI sessions, save them to a file. Click the down arrow and select Save Parameter Values, then specify the location and filename to save to. Note that some parameter types, such as rasters, vectors, and ROIs, will not be saved with the file. To apply the saved task settings, click the down arrow and select Restore Parameter Values, then select the file where you previously stored your settings.

  9. To run the process in the background, click the down arrow and select Run Task in the Background. If an ENVI Server has been set up on the network, the Run Task on remote ENVI Server name is also available. The ENVI Server Job Console will show the progress of the job and will provide a link to display the result when processing is complete. See ENVI Servers for more information.

  10. Click OK.

References

Welch, R. and W. Ehlers. "Merging Multiresolution SPOT HRV and Landsat TM Data." Photogrammetric Engineering & Remote Sensing 53, No. 3 (1987): 301-303.

See Also

CN Spectral Sharpening, Gram-Schmidt Pan Sharpening, NNDiffuse Pan Sharpening,