Addition and Subtraction of Images

Menu Command Operations/ Image Operation/ Add, Subtract and Advanced allow to add or subtract images. Using one of the command is followed by the appearance of the Window for the Selection of the Image (fig. 3.12(a)), which will be added to or subtracted from the current surface image. Press ``Select'' after you have selected an image. If the Commands Add or Subtract was in process, the image subtraction or addition will be performed at once. It is regarded that left lower corners of the images coincides, the new height of each point in the resultant image will be equal to half of the sum or to half of the difference of the points height of the initial images.

Figure: Dialogue for Image Addition and Subtraction. Left - Image Selection, Right - Window for Image Addition with Extended Options.

Additional Window appears, if The Command Advanced is selected (fig. 3.12(b)). It is possible in this case to shift the red rectangular (the first image) over the black rectangular (the second image) just in the field where they are presented. The shift may be performed in equal way by changing the parameters Xo and Yo, which are the difference in the coordinates (in pixels) of left lower corners of the images. The parameters Scale 1 and Scale 2 defines the way, how the height of the points of the resultant image will be calculated. Here is the corresponding formula $Z=(Scale 1)\cdot Z_{1}+(Scale 2)\cdot Z_{2}$.

Please pay attention, the values along Z axis may be in different units for different images. Besides height units other units (current, voltage, friction etc) may be used. In most cases there is no sense to add such values.