layout: default title: add8bit parent: Grid Tools nav_order: 2 —

add8bit

Description

add8bit is a command-line utility that combines two JHC-format 8-bit grid files (.8bit files). It can either add the values of the second file (scaled) to the first file, or find the maximum value between corresponding pixels of the two files. The output is a new 8-bit grid file.

Usage 

add8bit [OPTIONS] -first <file1.8bit> -second <file2.8bit> -out <output.8bit>

Arguments

Option Description Default / Example
-first <file1.8bit> Required. Specifies the path to the first input JHC-format 8-bit grid file. grid1.8bit
-second <file2.8bit> Required. Specifies the path to the second input JHC-format 8-bit grid file. grid2.8bit
-out <output.8bit> Required. Specifies the path for the output JHC-format 8-bit grid file. combined_grid.8bit
-max If specified, the output pixel value will be the maximum of the corresponding pixel values from the two input files. If not specified, the values are added (after scaling). (Addition is default)
-totalscale <value> A scaling factor applied to the final calculated value (after addition or max operation). 1.0
-firstscale <value> or -scale <value> A scaling factor applied to the second input file’s pixel values before they are added to the first file’s values. 1.0
-centre <value> A center value that is subtracted from the second file’s pixel values before scaling and addition. This allows for shifting the “zero” point of the second grid. 128.0

How It Works

  1. File Opening: Opens the two input JHC 8-bit grid files (-first, -second) and the output 8-bit grid file (-out).
  2. Header Reading: Reads the JHC_header from both input files, ensuring their dimensions match.
  3. Pixel-wise Operation: Iterates through each pixel in the input grids:
    • Reads the 8-bit pixel values from the first and second input files.
    • Applies firstscale to the second pixel value and subtracts centre.
    • If -max is specified, the output pixel value is the maximum of the (unscaled) first pixel and the (scaled) second pixel.
    • Otherwise (default addition), the output pixel value is the sum of the (unscaled) first pixel and the (scaled) second pixel.
    • The result is then multiplied by totalscale and clamped to the valid 8-bit range (0-254).
  4. Output Header: Creates a JHC_header for the output file (copied from the first input file’s header, but with updated min_value and max_value) and writes it to the output file.
  5. Output Data: Writes the processed 8-bit pixel data to the output file.

Output Files

  • <output.8bit>: A new JHC-format 8-bit grid file.

Dependencies

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

Notes

The scale option is an alias for firstscale. centre can be used to effectively shift the dynamic range of the second grid before combination. totalscale scales the final result.