Generally, the algebraic operation is used to process multi-spectral images to enhance a certain information, so as to easy pickup target characteristics and the changed area.
The operation procedure is explained as follows:
Enter the system main interface, then select (or assign) the first image (that is augend, minuend, or dividend in operation) participated in the algebraic operation. Please refer to Date Input for details.
Click on the channel participated in operation in the File panel, then click on Channel property page of the Property panel, click None button at the right side of Algebra, the submenu will appear, as shown in figure.
In which:
None: It indicates not to do algebraic operation. When you click this item, the browse icon above the Algebra and the pull down box will change to gray, i.e. the image will not participate in algebraic operation. By default, the system will select this item.
Add Image: Adding operation between two images i.e. take the average gray value of homologous pixels.
Sub Image: Subtracting operation between two images i.e. subtract the gray values of homologous pixels to pick up the difference between two images, which can be used to make change detection.
Divide Image: Dividing operation between two images, i.e. divide the gray values of homologous pixels, which can non linear exaggerate the contrast of different ground objects, eliminate the shadow and stand out the image.
And Image: Logical and operation between two images based on the bits. Generally, it is used to analysis the texture and noise in the image.
NOTE: users should make the templet of the second band image based on the requirements.
Or Image: Logical or operation between two images based on the bits. Generally, it is used to analysis the texture and noise in the image.
Index of Plant: It is used to check the area covered by the vegetation.
NOTE: users should make the templet of the second band image based on the requirements.
Select the corresponding menu
option for algebraic operation. Here the icon 
above
the Algebra and the pull down box will be activated.
Click the icon 
above the Algebra, then select the second image
in the pop up open dialog box (i.e. the addend, subtrahend or divisor),
click OK button, then assign a band in the pull down box at the
right side of the icon, as shown in figure. The system will complete the
operation automatically and display the result in image display window
in real time.
NOTE:
In the figure, it lists the first image with its band number (the upper box) and the second image with its band number (the lower box). The band number is determined by the number of image bands and its serial number takes band_1, band_2, band_3 in turn to correspond with each band of images. If the image is a single band or just processing one band, then merely band_1 is included.
Users select the type of operation or the second image and its band number (the first image and its band number is not changed), there will display the result in image display window in real time.
If users change (i.e. resetting) the first image and the band number, it must reset the second image and its band number too.