In this article I'll show how to make a CLI application to perform color correction based on a QP203 color chart. The details about the color correction itself is explained in this article. This application have three functionalities: extract a QP203 color chart from a picture; use the extracted color chart to correct the colors of the picture; apply the same color correction to different pictures. It is then possible with this application to correct the colors to match those of the reference QP203 or to match those of another picture; and to perform the correction on pictures including or not the QP203 color chart (i.e. using one shot including the card for reference and correcting another shot without the card but in the same sooting environment).

(The complete code is available at the end of the article)

Define a structure to hold the application data.

// App structure typedef struct App { // Return code at the end of execution int ret; // Arguments parser CapyArgParser* parser; // Input image and its path char const* pathImg; CapyImg* img; // Flag to memorise the verbose mode bool flagVerbose; // Coordinates in pixel of the chart corners in the image CapyImgPos chartCoord[4]; // Appli name char* name; } App;

The structure of the main() body looks as usual, create the app instance and wrap the body in a try/catch block:

// Main function int main( int argc, char** argv) { // Set the conversion function for raised exceptions CapyAddExcToStrFun(ExcToStr); // Create the instance of the application struct App app = { .ret = EXIT_SUCCESS, .parser = NULL, .pathImg = NULL, .img = NULL, .flagVerbose = false, .name = argv[0], }; try { ... } catchDefault { // Inform the user about the raised exception $(&capyDecoratorRed, fprintf)( stdout, "Sorry, an exception occured. Exiting.\n"); $(&capyDecoratorRed, fprintf)( stdout, "%s\n", CapyExcToStr(CapyGetLastExcId())); app.ret = EXIT_FAILURE; } endCatch; return app.ret; }

The command line arguments definition is as follow:

// Definition of the arguments from the command line CapyArg args[] = { {.lbl=argv[0], .nbVal=capyArg_noVal, .help="Apply color correction to an image based on a QP203 " "color chart.\n" "Examples:\n" " Correct an image containing a QP203 color chart to " "match the QP203 reference values:\n" " qp203corr -i img.png -c qp203 -o result.png\n" " Correct an image containing a QP203 color chart at " "given position to match the QP203 reference values:\n" " qp203corr -i img.png 10 20 20 20 20 40 10 40 -c qp203 " "-o result.png\n" " Extract QP203 color chart from img1.png and correct " "img2.png, also containing a QP203 color chart, to match " "their colors, then save the corrected image:\n" " qp203corr -i img1.png -e chart.dat && qp203corr -i " "img2.png -c chart.dat -o result.png\n" " Extract QP203 color chart from img1.png and correct " "img2.png, also containing a QP203 color chart, to match " "their colors, then save the correction matrix:\n" " qp203corr -i img1.png -e chart.dat && qp203corr -i " "img2.png -c chart.dat -m matrix.dat\n" " Apply a correction matrix to an image containing no " "QP203 color chart and save the corrected image:\n" " qp203corr -i img.png -a matrix.dat -o result.png"}, {.lbl="--in", .shortLbl="-i", .nbVal=capyArg_variableNbVal, .help="Followed by the path to the input image and, if used in " "extract or correction mode, by the color chart's corners " "position, from top-left clock wise, as x1 y1 x2 y2 x3 y3 " "x4 y4, integer coordinates in pixel from top left corner"}, {.lbl="--extract", .shortLbl="-e", .nbVal=1, .help="Followed by the path to the output color chart file.\n" "Extract a color chart from the image specified by -i and " "save the result to a color char file."}, {.lbl="--correct", .shortLbl="-c", .nbVal=1, .help="Followed by the path to the reference color chart.\n" "If the path is 'qp203', the values of the reference " "QP203 color chart are used instead.\n" "Correct the input image (-i) to match the reference " "color chart (-r) and save the corrected image and/or " "the correction matrix file."}, {.lbl="--out", .shortLbl="-o", .nbVal=1, .help="Followed by the path to the output corrected image."}, {.lbl="--matrix", .shortLbl="-m", .nbVal=1, .help="Followed by the path to the output matrix correction " "file."}, {.lbl="--apply", .shortLbl="-a", .nbVal=1, .help="Followed by the path to a matrix correction file.\n" "Apply the matrix correction file to the input image -i " "and save the corrected image.\n" "The matrix correction file can be created using -c and " "-m"}, {.lbl="--verbose", .shortLbl="-v", .nbVal=capyArg_noVal, .help="Print info on stdout"}, };

Then we decode the arguments and check them:

// Create the argument parser and parse the arguments app.parser = CapyArgParserAlloc(argc, argv, args); // Check the arguments if ($(app.parser, isSet)("-e") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 9)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-c") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 9)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-a") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 1)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-e") == true && $(app.parser, isSet)("-c") == true) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-e") == true && $(app.parser, isSet)("-a") == true) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-c") == true && $(app.parser, isSet)("-a") == true) raiseExc(excInvalidArgs);

And we call the appropriate function depending on the mode of the application.

// Init the appli InitApp(&app); // Run the appli if ($(app.parser, isSet)("-e")) RunAppExtract(&app); else if ($(app.parser, isSet)("-c")) RunAppCorrect(&app); else if ($(app.parser, isSet)("-a")) RunAppApply(&app);

The exception management is setup as follow.

// App exceptions enum AppExceptions { excNoImg = CapyExc_LastID, excInvalidArgs, lastAppException }; // Label for the AppExceptions char* exceptionStr[] = { "Couldn't load the image", "Invalid arguments, check the usage with --help" }; char const* ExcToStr(int16_t exc) { // If the exception ID is one of AppExceptions, // return the exception's label if (exc >= excNoImg && exc < lastAppException) return exceptionStr[exc - excNoImg]; // Else, the exception ID is not one of AppExceptions, return NULL else return NULL; }

An initialisation function is made to commonalise the code shared by all three modes: memorising the verbose flag and loading the input image.

// Appli initialisation void InitApp(App* const app) { // Memorise the verbose mode app->flagVerbose = $(app->parser, isSet)("-v"); // Load the input image app->pathImg = $(app->parser, getAsStr)("-i", 0); try { app->img = CapyImgAllocFromPNGPath(app->pathImg); } endCatch; if (app->img == NULL) raiseExc(excNoImg); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" == QP203Corrector =="); println(" Input image: %s", app->pathImg); } }

The extraction itself is done in its own function as it will be reused in correction mode.

// Extract the color chart at given coordinates from the image in // argument. CapyColorChart Extract(App* const app) { // Copy the chart's corners coordinates loop (i, 4) loop (j, 2) app->chartCoord[i].pos[j] = $(app->parser, getAsInt)("-i", 1 + i * 2 + j); // If the app is in verbose mode, print info if (app->flagVerbose) println( " Chart corners: (%u,%u),(%u,%u),(%u,%u),(%u,%u)", app->chartCoord[0].x,app->chartCoord[0].y, app->chartCoord[1].x,app->chartCoord[1].y, app->chartCoord[2].x,app->chartCoord[2].y, app->chartCoord[3].x,app->chartCoord[3].y); // Extract the chart from the input image CapyColorChart imgChart = CapyColorChartCreate(capyColorChart_QP203); $(&imgChart, extract)(app->img, app->chartCoord); // Return the color chart return imgChart; }

The extraction mode extracts the color chart at given coordinates from the image in argument and save it.

// Run the appli in extract mode void RunAppExtract(App* const app) { // Extract the chart CapyColorChart imgChart = Extract(app); // Save the chart char const* pathChart = $(app->parser, getAsStr)("-e", 0); try { $(&imgChart, saveToPath)(pathChart); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathChart); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" Color chart:"); loop (iRow, imgChart.nbRow) { printf(" "); loop (iCol, imgChart.nbCol) { int idx = iRow * imgChart.nbCol + iCol; printf( "(%.3lf,%.3lf,%.3lf),", imgChart.colors[idx].rgb[0], imgChart.colors[idx].rgb[1], imgChart.colors[idx].rgb[2]); } printf("\n"); } println( " Save the chart color to %s", pathChart); } }

The correction mode first extracts the color chart at given coordinates from the image in argument.

// Run the appli in correction mode void RunAppCorrect(App* const app) { // Extract the chart CapyColorChart imgChart = Extract(app); ... }

Then it creates the reference chart. It is either loaded from a file resulting from a previous extraction (when we want to match a picture to another picture), or it is the reference values of the QP203 color chart.

// Get the path to the reference color chart char const* pathRefChart = $(app->parser, getAsStr)("-c", 0); // Create the reference color chart CapyColorChart refChart = CapyColorChartCreate(capyColorChart_QP203); // If the reference color chart is not the reference QP203 color // chart, load the user reference try { if (strcmp(pathRefChart, "qp203") != 0) $(&refChart, loadFromPath)(pathRefChart); } catchDefault { if (app->flagVerbose) println("Failed to load %s", pathRefChart); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" Reference color chart:"); loop (iRow, refChart.nbRow) { printf(" "); loop (iCol, refChart.nbCol) { int idx = iRow * refChart.nbCol + iCol; printf( "(%.3lf,%.3lf,%.3lf),", refChart.colors[idx].rgb[0], refChart.colors[idx].rgb[1], refChart.colors[idx].rgb[2]); } printf("\n"); } } ...

Next, it matches the brightness of the reference color chart to the one of the image color chart chart to avoid burnt colors in underexposed pictures.

// Match the brightness of the reference chart to the brightness of // the image chart $(&refChart, matchBrightness)(&imgChart); ...

It can now calculate the color correction matrix.

// Calculate the correction matrix CapyColorCorrMat corrector = CapyColorCorrMatCreate(); CapyColorCorrMatchFitness resMatch = $(&corrector, match)(&imgChart, &refChart); // If the app is in verbose mode, print info if (app->flagVerbose) println( " Fitness: %.4lf -> %.4lf", resMatch.initialFitness, resMatch.finalFitness); ...

If the user requested to save the corrected image, apply the color correction matrix to the original image and save it.

// If the user requested to save the result image if ($(app->parser, isSet)("-o") == true) { // Apply the correction $(&corrector, apply)(app->img); // Save the corrected image char const* pathRes = $(app->parser, getAsStr)("-o", 0); try { $(app->img, saveToPathAsPNG)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); } ...

Finally if the user requested to save the color correction matrix, do it.

// If the user requested to save the correction matrix if ($(app->parser, isSet)("-m") == true) { // Save the correction matrix char const* pathRes = $(app->parser, getAsStr)("-m", 0); try { $(&corrector, saveToPath)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); }

In apply mode, we load a color correction matrix (created with the correction mode) and apply it to another picture.

// Run the appli in apply mode void RunAppApply(App* const app) { // Load the correction matrix CapyColorCorrMat corrector = CapyColorCorrMatCreate(); char const* pathMat = $(app->parser, getAsStr)("-a", 0); try { $(&corrector, loadFromPath)(pathMat); } catchDefault { if (app->flagVerbose) println("Failed to load %s", pathMat); } endCatch; CapyForwardExc(); // If the user requested to save the result image if ($(app->parser, isSet)("-o") == true) { // Apply the correction $(&corrector, apply)(app->img); // Save the corrected image char const* pathRes = $(app->parser, getAsStr)("-o", 0); try { $(app->img, saveToPathAsPNG)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); } }

Everything put together, it becomes:

/* QP203Corr - A color correction app based on the QP203 color chart Copyright (C) 2022 Pascal Baillehache baillehache.pascal@gmail.com https://baillehachepascal.dev This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <LibCapy/capy.h> // App exceptions enum AppExceptions { excNoImg = CapyExc_LastID, excInvalidArgs, lastAppException }; // Label for the AppExceptions char* exceptionStr[] = { "Couldn't load the image", "Invalid arguments, check the usage with --help" }; char const* ExcToStr(int16_t exc) { // If the exception ID is one of AppExceptions, // return the exception's label if (exc >= excNoImg && exc < lastAppException) return exceptionStr[exc - excNoImg]; // Else, the exception ID is not one of AppExceptions, return NULL else return NULL; } // App structure typedef struct App { // Return code at the end of execution int ret; // Arguments parser CapyArgParser* parser; // Input image and its path char const* pathImg; CapyImg* img; // Flag to memorise the verbose mode bool flagVerbose; // Coordinates in pixel of the chart corners in the image CapyImgPos chartCoord[4]; // Appli name char* name; } App; // Appli initialisation void InitApp(App* const app) { // Memorise the verbose mode app->flagVerbose = $(app->parser, isSet)("-v"); // Load the input image app->pathImg = $(app->parser, getAsStr)("-i", 0); try { app->img = CapyImgAllocFromPNGPath(app->pathImg); } endCatch; if (app->img == NULL) raiseExc(excNoImg); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" == QP203Corrector =="); println(" Input image: %s", app->pathImg); } } // Extract the color chart at given coordinates from the image in // argument. CapyColorChart Extract(App* const app) { // Copy the chart's corners coordinates loop (i, 4) loop (j, 2) app->chartCoord[i].pos[j] = $(app->parser, getAsInt)("-i", 1 + i * 2 + j); // If the app is in verbose mode, print info if (app->flagVerbose) println( " Chart corners: (%u,%u),(%u,%u),(%u,%u),(%u,%u)", app->chartCoord[0].x,app->chartCoord[0].y, app->chartCoord[1].x,app->chartCoord[1].y, app->chartCoord[2].x,app->chartCoord[2].y, app->chartCoord[3].x,app->chartCoord[3].y); // Extract the chart from the input image CapyColorChart imgChart = CapyColorChartCreate(capyColorChart_QP203); $(&imgChart, extract)(app->img, app->chartCoord); // Return the color chart return imgChart; } // Run the appli in extract mode void RunAppExtract(App* const app) { // Extract the chart CapyColorChart imgChart = Extract(app); // Save the chart char const* pathChart = $(app->parser, getAsStr)("-e", 0); try { $(&imgChart, saveToPath)(pathChart); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathChart); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" Color chart:"); loop (iRow, imgChart.nbRow) { printf(" "); loop (iCol, imgChart.nbCol) { int idx = iRow * imgChart.nbCol + iCol; printf( "(%.3lf,%.3lf,%.3lf),", imgChart.colors[idx].rgb[0], imgChart.colors[idx].rgb[1], imgChart.colors[idx].rgb[2]); } printf("\n"); } println( " Save the chart color to %s", pathChart); } } // Run the appli in correction mode void RunAppCorrect(App* const app) { // Extract the chart CapyColorChart imgChart = Extract(app); // Get the path to the reference color chart char const* pathRefChart = $(app->parser, getAsStr)("-c", 0); // Create the reference color chart CapyColorChart refChart = CapyColorChartCreate(capyColorChart_QP203); // If the reference color chart is not the reference QP203 color // chart, load the user reference try { if (strcmp(pathRefChart, "qp203") != 0) $(&refChart, loadFromPath)(pathRefChart); } catchDefault { if (app->flagVerbose) println("Failed to load %s", pathRefChart); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) { println(" Reference color chart:"); loop (iRow, refChart.nbRow) { printf(" "); loop (iCol, refChart.nbCol) { int idx = iRow * refChart.nbCol + iCol; printf( "(%.3lf,%.3lf,%.3lf),", refChart.colors[idx].rgb[0], refChart.colors[idx].rgb[1], refChart.colors[idx].rgb[2]); } printf("\n"); } } // Match the brightness of the reference chart to the brightness of // the image chart $(&refChart, matchBrightness)(&imgChart); // Calculate the correction matrix CapyColorCorrMat corrector = CapyColorCorrMatCreate(); CapyColorCorrMatchFitness resMatch = $(&corrector, match)(&imgChart, &refChart); // If the app is in verbose mode, print info if (app->flagVerbose) println( " Fitness: %.4lf -> %.4lf", resMatch.initialFitness, resMatch.finalFitness); // If the user requested to save the result image if ($(app->parser, isSet)("-o") == true) { // Apply the correction $(&corrector, apply)(app->img); // Save the corrected image char const* pathRes = $(app->parser, getAsStr)("-o", 0); try { $(app->img, saveToPathAsPNG)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); } // If the user requested to save the correction matrix if ($(app->parser, isSet)("-m") == true) { // Save the correction matrix char const* pathRes = $(app->parser, getAsStr)("-m", 0); try { $(&corrector, saveToPath)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); } } // Run the appli in apply mode void RunAppApply(App* const app) { // Load the correction matrix CapyColorCorrMat corrector = CapyColorCorrMatCreate(); char const* pathMat = $(app->parser, getAsStr)("-a", 0); try { $(&corrector, loadFromPath)(pathMat); } catchDefault { if (app->flagVerbose) println("Failed to load %s", pathMat); } endCatch; CapyForwardExc(); // If the user requested to save the result image if ($(app->parser, isSet)("-o") == true) { // Apply the correction $(&corrector, apply)(app->img); // Save the corrected image char const* pathRes = $(app->parser, getAsStr)("-o", 0); try { $(app->img, saveToPathAsPNG)(pathRes); } catchDefault { if (app->flagVerbose) println("Failed to save %s", pathRes); } endCatch; CapyForwardExc(); // If the app is in verbose mode, print info if (app->flagVerbose) println(" Save the corrected image to %s", pathRes); } } // Main function int main( int argc, char** argv) { // Set the conversion function for raised exceptions CapyAddExcToStrFun(ExcToStr); // Create the instance of the application struct App app = { .ret = EXIT_SUCCESS, .parser = NULL, .pathImg = NULL, .img = NULL, .flagVerbose = false, .name = argv[0], }; try { // Definition of the arguments from the command line CapyArg args[] = { {.lbl=argv[0], .nbVal=capyArg_noVal, .help="Apply color correction to an image based on a QP203 " "color chart.\n" "Examples:\n" " Correct an image containing a QP203 color chart to " "match the QP203 reference values:\n" " qp203corr -i img.png -c qp203 -o result.png\n" " Correct an image containing a QP203 color chart at " "given position to match the QP203 reference values:\n" " qp203corr -i img.png 10 20 20 20 20 40 10 40 -c qp203 " "-o result.png\n" " Extract QP203 color chart from img1.png and correct " "img2.png, also containing a QP203 color chart, to match " "their colors, then save the corrected image:\n" " qp203corr -i img1.png -e chart.dat && qp203corr -i " "img2.png -c chart.dat -o result.png\n" " Extract QP203 color chart from img1.png and correct " "img2.png, also containing a QP203 color chart, to match " "their colors, then save the correction matrix:\n" " qp203corr -i img1.png -e chart.dat && qp203corr -i " "img2.png -c chart.dat -m matrix.dat\n" " Apply a correction matrix to an image containing no " "QP203 color chart and save the corrected image:\n" " qp203corr -i img.png -a matrix.dat -o result.png"}, {.lbl="--in", .shortLbl="-i", .nbVal=capyArg_variableNbVal, .help="Followed by the path to the input image and, if used in " "extract or correction mode, by the color chart's corners " "position, from top-left clock wise, as x1 y1 x2 y2 x3 y3 " "x4 y4, integer coordinates in pixel from top left corner"}, {.lbl="--extract", .shortLbl="-e", .nbVal=1, .help="Followed by the path to the output color chart file.\n" "Extract a color chart from the image specified by -i and " "save the result to a color char file."}, {.lbl="--correct", .shortLbl="-c", .nbVal=1, .help="Followed by the path to the reference color chart.\n" "If the path is 'qp203', the values of the reference " "QP203 color chart are used instead.\n" "Correct the input image (-i) to match the reference " "color chart (-r) and save the corrected image and/or " "the correction matrix file."}, {.lbl="--out", .shortLbl="-o", .nbVal=1, .help="Followed by the path to the output corrected image."}, {.lbl="--matrix", .shortLbl="-m", .nbVal=1, .help="Followed by the path to the output matrix correction " "file."}, {.lbl="--apply", .shortLbl="-a", .nbVal=1, .help="Followed by the path to a matrix correction file.\n" "Apply the matrix correction file to the input image -i " "and save the corrected image.\n" "The matrix correction file can be created using -c and " "-m"}, {.lbl="--verbose", .shortLbl="-v", .nbVal=capyArg_noVal, .help="Print info on stdout"}, }; // Create the argument parser and parse the arguments app.parser = CapyArgParserAlloc(argc, argv, args); // Check the arguments if ($(app.parser, isSet)("-e") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 9)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-c") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 9)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-a") == true && ($(app.parser, isSet)("-i") == false || $(app.parser, getNbVal)("-i") != 1)) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-e") == true && $(app.parser, isSet)("-c") == true) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-e") == true && $(app.parser, isSet)("-a") == true) raiseExc(excInvalidArgs); if ($(app.parser, isSet)("-c") == true && $(app.parser, isSet)("-a") == true) raiseExc(excInvalidArgs); // Init the appli InitApp(&app); // Run the appli if ($(app.parser, isSet)("-e")) RunAppExtract(&app); else if ($(app.parser, isSet)("-c")) RunAppCorrect(&app); else if ($(app.parser, isSet)("-a")) RunAppApply(&app); } catchDefault { // Inform the user about the raised exception $(&capyDecoratorRed, fprintf)( stdout, "Sorry, an exception occured. Exiting.\n"); $(&capyDecoratorRed, fprintf)( stdout, "%s\n", CapyExcToStr(CapyGetLastExcId())); app.ret = EXIT_FAILURE; } endCatch; return app.ret; }

Compile with the following Makefile:

CAPY_PARAM=-std=c18 -I./ -Wall -Wextra -Wshadow -Wno-format-truncation -Werror -Wfatal-errors -O3 -ggdb -fopenmp -DPNG_SKIP_SETJMP_CHECK `pkg-config --cflags gtk+-3.0` -D_XOPEN_SOURCE=700 -DCAPY_WITH_GUI=1 CAPY_LINK=-lcapy -lm -fopenmp -lpng `pkg-config --libs gtk+-3.0` qp203corr: main.o Makefile gcc -o qp203corr main.o $(CAPY_LINK) main.o: main.c Makefile gcc -c main.c $(CAPY_PARAM)

Example of use:

Extract a color chart from the picture img00.png and save it to the file img00.chart: qp203corr -i img00.png 501 215 654 199 674 389 507 405 -e img00.chart -v Correct the colors of picture img00.png to match the reference colors, save the correction matrix to img00.mat, and save the corrected picture to img00corr.png: qp203corr -i img00.png 501 215 654 199 674 389 507 405 -c qp203 -o img00corr.png -m img00.mat -v Correct the colors of picture img00.png to match the color chart img01.chart and save the corrected picture to img00corr.png: qp203corr -i img00.png 501 215 654 199 674 389 507 405 -c img01.chart -o img00corr.png -v Apply the color correction matrix img01.mat to the picture img00.png and save the corrected picture to img00corr.png: qp203corr -i img00.png -a img01.mat -o img00corr.png -v

See the related article for examples of corrected pictures.