filterAerial

Description

filterAerial is a utility designed to process multiple 8-bit aerial image files (presumably representing intensity or depth data, potentially from Optech systems) and compute an average image. This average image can then be used to remove low-frequency noise, such as solar radiation effects, from individual aerial photographs.

The tool reads multiple input 8-bit image files, sums their pixel values, and then divides by the number of input files to get an average for each pixel.

Usage 

filterAerial -out <outfile> <8bitfile(s)>

Arguments

Option Description
-out <outfile> Required. The path for the output averaged 8-bit image file.
<8bitfile(s)> Required. One or more paths to input 8-bit image files. All input files are assumed to have identical dimensions and JHC headers.

How It Works

  1. Initialization: Initializes variables and an array sum_matrix (1201x1601) to accumulate pixel sums.
  2. Output File Creation: Creates the specified output file (-out) for writing the averaged image.
  3. Header Processing:
    • Opens the first input 8-bit image file to read its JHC header (head_in).
    • Copies head_in to head_out (which will be the header for the output file).
    • Verifies that head_in.data_type is 1 (indicating an 8-bit file).
    • Allocates memory for fout (output row buffer) and fsum (row sum buffer, though sum_matrix is used for 2D sums).
    • Writes head_out to the outfile.
  4. Input File Iteration (Accumulate Pixel Sums): Loops through each input 8-bit image file:
    • Opens the current input file.
    • Reads its JHC header (head_in) (ensuring consistency in case headers differ subtly between inputs, though dimensions are assumed identical).
    • Allocates memory for fin (input row buffer).
    • Iterates through each row (i) and column (j) of the image:
      • Reads a row of pixel data into fin.
      • Adds the value of each pixel *(fin + j) to sum_matrix[i][j].
    • Closes the current input file.
  5. Average Pixel Values and Write Output:
    • Seeks to the data section of the outfile (after the JHC header).
    • Iterates through each row (i) and column (j) of the image:
      • Calculates the average pixel value (unsigned char)(sum_matrix[i][j] / noin).
      • Writes this averaged pixel value to fout.
      • After processing a row, writes fout to outfile.
  6. Cleanup: Closes the output file.

Output Files

  • <outfile>: An 8-bit JHC-format image file containing the averaged pixel values.

Dependencies

  • array.h: For JHC_header structure.
  • support.h: For general utility functions and error handling.

Notes

This technique is useful for removing systematic, low-frequency noise (such as uneven illumination) that is consistent across multiple images of the same area. The resulting average image can then be subtracted from individual images to produce a cleaner, destriped output. The tool assumes all input images have identical dimensions.