% VIEWLABSPACE Visualisation of L*a*b* space % % Usage: viewlabspace(dL) % % Argument: dL - Optional increment in lightness with each slice of L*a*b* % space. Defaults to 5 % % Function allows interactive viewing of a sequence of images corresponding to % different slices of lightness in L*a*b* space. Lightness varies from 0 to % 100. Initially a slice at a lightness of 50 is displayed. % Pressing 'l' or arrow up/right will increase the lightness by dL. % Pressing 'd' or arrow down/left will darken by dL. % Press 'x' to exit. % % The CIELAB colour coordinates of the cursor position within the slice images % is updated continuously. This is useful for determining suitable controls % points for the definition of colourmap paths through CIELAB space. % % See also: COLOURMAPPATH, ISOCOLOURMAPPATH, CMAP % Copyright (c) 2013 Peter Kovesi % Centre for Exploration Targeting % The University of Western Australia % peter.kovesi at uwa edu au % % Permission is hereby granted, free of charge, to any person obtaining a copy % of this software and associated documentation files (the "Software"), to deal % in the Software without restriction, subject to the following conditions: % % The above copyright notice and this permission notice shall be included in % all copies or substantial portions of the Software. % % The Software is provided "as is", without warranty of any kind. % March 2013 % November 2013 Interactive CIELAB coordinate feedback from mouse position function viewlabspace(dL, figNo) if ~exist('dL', 'var'), dL = 5; end if ~exist('figNo', 'var'), figNo = 100; end % Define some reference colours in rgb rgb = [1 0 0 0 1 0 0 0 1 1 1 0 0 1 1 1 0 1 1 .5 0 .5 0 1 0 .5 1 0 1 .5 1 0 .5]; colours = {'red ' 'green ' 'blue ' 'yellow ' 'cyan ' 'magenta' 'orange ' 'violet ' 'blue-cyan' 'green-cyan' 'red-magenta'}; % ... and convert them to lab % Use D65 whitepoint to match typical monitors. wp = whitepoint('D65'); labv = applycform(rgb, makecform('srgb2lab', 'AdaptedWhitePoint', wp)); % Obtain cylindrical coordinates in lab space labradius = sqrt(labv(:,2).^2+labv(:,3).^2); labtheta = atan2(labv(:,3), labv(:,2)); % Define a*b* grid for image scale = 2; [a, b] = meshgrid([-127:1/scale:127]); [rows,cols] = size(a); % Scale and offset lab coords to fit image coords labc = zeros(size(labv)); labc(:,1) = round(labv(:,1)); labc(:,2) = round(scale*labv(:,2) + cols/2); labc(:,3) = round(scale*labv(:,3) + rows/2); % Print out lab values labv = round(labv); fprintf('\nCoordinates of standard colours in L*a*b* space\n\n'); for n = 1:length(labv) fprintf('%s L%3d a %4d b %4d angle %4.1f radius %4d\n',... colours{n}, ... labv(n,1), labv(n,2), ... labv(n,3), labtheta(n), round(labradius(n))); end fprintf('\n\n') % Generate axis tick values tickval = [-100 -50 0 50 100]; tickcoords = scale*tickval + cols/2; ticklabels = {'-100'; '-50'; '0'; '50'; '100'}; fig = figure(figNo); set(fig, 'WindowButtonMotionFcn', @labcoords) set(fig, 'KeyReleaseFcn', @keyreleasecb); texth = text(50, 50,'', 'color', [1 1 1]); % Text area to display % current a and b values fprintf('Place cursor within figure\n'); fprintf('Press ''l'' to lighten, ''d'' to darken, or use arrow keys\n'); fprintf('''x'' to exit\n'); L = 50; renderlabslice(L); %------------------------------------------------------ % Window button move call back function function labcoords(src, evnt) cp = get(gca,'CurrentPoint'); x = cp(1,1); y = cp(1,2); aval = round((x-(cols/2))/scale); bval = round((y-(rows/2))/scale); radius = sqrt(aval.^2 + bval.^2); hue = atan2(bval, aval); set(texth, 'String', sprintf('a %d b %d radius %d angle %d',... aval, bval, round(radius), round(hue/pi*180))); set(texth, 'fontsize', 13, 'fontweight', 'bold'); end %----------------------------------------------------------------------- % Key Release callback % If '+' or up is pressed we move up in lighness % '-' or down moves us down in lightness function keyreleasecb(src,evnt) if evnt.Character == 'l' | evnt.Character == 30 L = min(L + dL, 100); elseif evnt.Character == 'd' | evnt.Character == 31 L = max(L - dL, 0); elseif evnt.Character == 's' % Save slice as an image tmp = rgb; tmp(:,:,1) = flipud(tmp(:,:,1)); tmp(:,:,2) = flipud(tmp(:,:,2)); tmp(:,:,3) = flipud(tmp(:,:,3)); % Draw a red cross at the achromatic point [r,c,~] = size(tmp); tmp = imageline(tmp, [c/2-5, r/2], [c/2+5, r/2], [255, 0 0]); tmp = imageline(tmp, [c/2, r/2-5], [c/2, r/2+5], [255, 0 0]); imwrite(tmp, sprintf('LAB_slice_L_%d.png',L)); elseif evnt.Character == 'x' delete(figNo); return end renderlabslice(L); % Render a slice at this new lightness level labcoords(src, evnt); % Regenerate the cursor coordinates end %-------------------------------------------------------- function renderlabslice(L) % Build image in lab space lab = zeros(rows,cols,3); lab(:,:,1) = L; lab(:,:,2) = a; lab(:,:,3) = b; wp = whitepoint('D65'); % Generate rgb values from lab rgb = applycform(lab, makecform('lab2srgb', 'AdaptedWhitePoint', wp)); % Invert to reconstruct the lab values lab2 = applycform(rgb, makecform('srgb2lab', 'AdaptedWhitePoint', wp)); % Where the reconstructed lab values differ from the specified values is % an indication that we have gone outside of the rgb gamut. Apply a % mask to the rgb values accordingly mask = max(abs(lab-lab2),[],3); for n = 1:3 rgb(:,:,n) = rgb(:,:,n).*(mask<2); % tolerance of 1 end figure(figNo), image(rgb), title(sprintf('Lightness %d', L)); axis square, axis xy % Recreate the text handle in the new image texth = text(50, 50,'', 'color', [1 1 1]); set(gca, 'xtick', tickcoords); set(gca, 'ytick', tickcoords); set(gca, 'xticklabel', ticklabels); set(gca, 'yticklabel', ticklabels); xlabel('a*'); ylabel('b*'); hold on, plot(cols/2, rows/2, 'r+'); % Centre point for reference % Plot reference colour positions for n = 1:length(labc) plot(labc(n,2), labc(n,3), 'w+') text(labc(n,2), labc(n,3), ... sprintf(' %s\n %d %d %d ',colours{n},... labv(n,1), labv(n,2), labv(n,3)),... 'color', [1 1 1], 'fontsize', 12) end hold off end %-------------------------------------------------------- end % of viewlabspace