rawToRGB.m

%%
%% Returns RGB pixel values from a flat raw image buffer. This routine handles
%% all CFA pattern types but is typically used for Fuji x-trans since bayer
%% images can be handled with much simpler logic
%%
%% Parameters:
%%
%% cfaPatternDimensions - 1D array describing [#rows, #cols] in the CFA pattern.
%% For fuji this would be [6 6]
%%
%% cfaPatternExif - 1D array containing CFA pattern from EXIF data. This is a flat
%% array - this routine will use 'cfaPatternDimensions' to determine the
%% pixel columns and rows of the CFA pattern. For example, the Fuji x-trans pattern
%% is [0 2 1 2 0 1 1 1 0 1 1 2 1 1 2 1 1 0 2 0 1 0 2 1 1 1 2 1 1 0 1 1 0 1 1 2],
%% which will become the following when passed with a cfaPatternDimensions of [6 6]:
%%
%%   COL: 0 1 2 3 4 5
%% ROW 0: 0 2 1 2 0 1
%% ROW 1: 1 1 0 1 1 2
%% ROW 2: 1 1 2 1 1 0
%% ROW 3: 2 0 1 0 2 1
%% ROW 4: 1 1 2 1 1 0
%% ROW 5: 1 1 0 1 1 2
%%
%% Which corresponds to the following colors (red=0, green=1, blue=2 values above):
%%
%%   COL: 0 1 2 3 4 5
%% ROW 0: R B G B R G
%% ROW 1: G G R G G B
%% ROW 2: G G B G G R
%% ROW 3: B R G R B G
%% ROW 4: G G B G G R
%% ROW 5: G G R G G B
%%
%% imgData - Image data containing pixel values, the dimensions of which must
%% be even multiples of cfaPatternDimensions
%%
%% Returns three 1D arrays, corresponding to the red, green, and blue pixel
%% values
%%
%% Sample logic for calling this function. The TIFF file should be generated
%% from LibRaw's unprocessed_raw.exe with the -T option
%%
%% imgData = imread('rawdata.tiff'); %% read file created by unprocessed_raw.exe
%% imgData = imgData(:, 1:6032); %% trim to visible size, reported by unprocessed_raw.exe as "Image size"
%% [redPixels, greenPixels, bluePixels] = rawToRGB([6 6], %% CFA pattern dimensions of 6x6
%%    [0 2 1 2 0 1 1 1 0 1 1 2 1 1 2 1 1 0 2 0 1 0 2 1 1 1 2 1 1 0 1 1 0 1 1 2], %% CFA pattern as flat array
%%    imgData);
%%  printf("std: %.2f %.2f %.2f\n", std(redPixels), std(greenPixels), std(bluePixels)); %% print stdev
%%  printf("avg: %.2f %.2f %.2f\n", mean(redPixels), mean(greenPixels), mean(bluePixels)); %% print average
%%
function [redPixels, greenPixels, bluePixels] = rawToRGB(cfaPatternDimensions, cfaPatternExif, imgData)

  %%
  %% Returns array with zero-based pixel-column indexes for specified CFA
  %% color on the specified CFA pattern row.
  %%
  function colIndexesInRow = getPatternIndexes(row, cfaColor)
    colIndexesInRow = find(cfaPatternExif(1 + row*cfaPatternRows : (row+1)*cfaPatternRows)  == cfaColor) - 1; %% -1 to make zero-based
  end

  CFA_RED = 0;
  CFA_GREEN = 1;
  CFA_BLUE = 2;

  %%
  %% build array of pixel indexes for each color on each of the rows
  %% in the CFA pattern
  %%
  cfaPatternRows = cfaPatternDimensions(1);
  cfaPatternCols = cfaPatternDimensions(2);
  for row=0:cfaPatternRows-1
    redPixelColIndexesForRow{row+1} = getPatternIndexes(row, CFA_RED);
    greenPixelColIndexesForRow{row+1} = getPatternIndexes(row, CFA_GREEN);
    bluePixelColIndexesForRow{row+1} = getPatternIndexes(row, CFA_BLUE);
  end

  %%
  %% get RGB pixel values. Each iteration of the following loop handles all the
  %% rows corresponding to a CFA pattern rows. We're not looping for every
  %% every row in the image data - each iteration culls all the rows
  %% for a given CFA pattern row by utilizing vector ranges. We store the data
  %% for each color in a cell array - we can't use vectors because the number
  %% of pixel values will vary from row to row (vectors require equal dimensions)
  %%
  for row=0:cfaPatternRows-1
    red_rows{row+1}   = imgData(row+1:cfaPatternRows:end, ismember(mod(0:end-1, cfaPatternRows), redPixelColIndexesForRow{row+1}));
    green_rows{row+1} = imgData(row+1:cfaPatternRows:end, ismember(mod(0:end-1, cfaPatternRows), greenPixelColIndexesForRow{row+1}));
    blue_rows{row+1}  = imgData(row+1:cfaPatternRows:end, ismember(mod(0:end-1, cfaPatternRows), bluePixelColIndexesForRow{row+1}));
  end

  %% aggregate the RGB pixel value data from the cell array into 1D flat arrays
  redPixels = [red_rows{:}](:);
  greenPixels = [green_rows{:}](:);
  bluePixels  = [blue_rows{:}](:);
end