rgb = lab2rgb(lab);<\/span><\/span><\/div><\/div><\/div><\/div>max(rgb(:))<\/span><\/span><\/div>ans = 1.1271<\/div><\/div><\/div>min(rgb(:))<\/span><\/span><\/div>ans = -0.1144<\/div><\/div><\/div><\/div>This led me to explore different ways to visualize which colors in a Lab curve are out of gamut. (Note that this discussion assumes that we are talking about sRGB, which is the default color space used by <\/span>lab2rgb<\/span>.) The first thing I tried was to add marks to the displayed colormap to indicate which colors are out-of-gamut. This next block of code finds all the contiguous segments of out-of-gamut colors in the colormap.<\/span><\/div>out_of_gamut_mask = any(rgb > 1,2) | any(rgb < 0,2);<\/span><\/span><\/div><\/div>d = diff([0 ; out_of_gamut_mask ; 0]);<\/span><\/span><\/div><\/div>first = find(d == 1)<\/span><\/span><\/div>first = <\/span>2\u00d71<\/span><\/div><\/div>     1\r\n   211\r\n<\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div>last = find(d == -1) - 1<\/span><\/span><\/div>last = <\/span>2\u00d71<\/span><\/div><\/div>    61\r\n   256\r\n<\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div>The values of <\/span>first<\/span> and <\/span>last<\/span> above mean that the Lab colors <\/span>lab(1:61,:)<\/span> and <\/span>lab(211:256,:)<\/span> are out of the sRGB gamut. Now use these numbers to add <\/span>gamut alarm<\/span> indicators (red bars) to the displayed colormap.<\/span><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>y = [1.25 1.25];<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    x1 = first(k) - 1;<\/span><\/span><\/div><\/div>    x2 = last(k);<\/span><\/span><\/div><\/div>    x = [x1 x2];<\/span><\/span><\/div><\/div>    plot(ax,x,y,<\/span>\"r\"<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold <\/span>off<\/span><\/span><\/div><\/div><\/div><\/div><\/div><\/div>Another visualization approach is to plot the red, green, and blue color component values returned by <\/span>lab2rgb<\/span> and show where those values are too high or too low.<\/span><\/div>figure<\/span><\/span><\/div><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>plot(rgb(:,1),<\/span>'r'<\/span>)<\/span><\/span><\/div><\/div>plot(rgb(:,2),<\/span>'g'<\/span>)<\/span><\/span><\/div><\/div>plot(rgb(:,3),<\/span>'b'<\/span>)<\/span><\/span><\/div><\/div>xlim([1 - 0.05*height(rgb), 1.05*height(rgb)]);<\/span><\/span><\/div><\/div>y1 = min(-0.2,ax.YLim(1));<\/span><\/span><\/div><\/div>y2 = max(1.2,ax.YLim(2));<\/span><\/span><\/div><\/div>ylim([y1 y2]);<\/span><\/span><\/div><\/div>grid(<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>yline(0, LineWidth = 5, Color = [0.7 0.7 0.7])<\/span><\/span><\/div><\/div>yline(1, LineWidth = 5, Color = [0.7 0.7 0.7])<\/span><\/span><\/div><\/div><\/div><\/div>too_high = any(rgb > 1,2);<\/span><\/span><\/div><\/div>k = find(too_high);<\/span><\/span><\/div><\/div>if <\/span>~isempty(k)<\/span><\/span><\/div><\/div>    plot(k,ones(size(k)),<\/span>'r*'<\/span>,MarkerSize = 6)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>too_low = any(rgb < 0,2);<\/span><\/span><\/div><\/div>k = find(too_low);<\/span><\/span><\/div><\/div>if <\/span>~isempty(k)<\/span><\/span><\/div><\/div>    plot(k,zeros(size(k)),<\/span>'r*'<\/span>,MarkerSize = 6)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold(<\/span>\"off\"<\/span>)<\/span><\/span><\/div><\/div>title(<\/span>\"RGB values with gamut alarm\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div><\/div><\/div>Next I want to show the <\/span>a<\/span> and <\/span>b<\/span> values for the out-of-gamut Lab curve colors.<\/span><\/div>plot(lab(:,2),lab(:,3));<\/span><\/span><\/div><\/div>axis <\/span>equal<\/span><\/span><\/div><\/div>xlim([-110 110])<\/span><\/span><\/div><\/div>ylim([-110 110])<\/span><\/span><\/div><\/div>ax = gca;<\/span><\/span><\/div><\/div>ax.XAxisLocation = <\/span>\"origin\"<\/span>;<\/span><\/span><\/div><\/div>ax.YAxisLocation = <\/span>\"origin\"<\/span>;<\/span><\/span><\/div><\/div>xlabel(<\/span>\"a\"<\/span>)<\/span><\/span><\/div><\/div>ylabel(<\/span>\"b\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    j1 = first(k);<\/span><\/span><\/div><\/div>    j2 = last(k);<\/span><\/span><\/div><\/div>    x = lab(j1:j2,2);<\/span><\/span><\/div><\/div>    y = lab(j1:j2,3);<\/span><\/span><\/div><\/div>    plot(x,y,<\/span>\"r\"<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold <\/span>off<\/span><\/span><\/div><\/div><\/div><\/div>grid(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>title(<\/span>\"a-b values with gamut alarm\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div><\/div><\/div>Finally, I want to show the <\/span>L<\/span> values for the out-of-gamut Lab curve colors.<\/span><\/div>plot(lab(:,1));<\/span><\/span><\/div><\/div>xlim([1 - 0.05*height(lab), 1.05*height(lab)]);<\/span><\/span><\/div><\/div>ylim([-10 110])<\/span><\/span><\/div><\/div><\/div><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    j1 = first(k);<\/span><\/span><\/div><\/div>    j2 = last(k);<\/span><\/span><\/div><\/div>    x = j1:j2;<\/span><\/span><\/div><\/div>    y = lab(j1:j2,1);<\/span><\/span><\/div><\/div>    plot(x,y,<\/span>\"r\"<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold <\/span>off<\/span><\/span><\/div><\/div><\/div><\/div>grid <\/span>on<\/span><\/span><\/div><\/div>title(<\/span>\"L values with gamut alarm\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div><\/div><\/div>I created some utility functions that generate these different plots. They are at the end of this post. I'll finish up by using <\/span>tiledlayout<\/span> to combine all four plots in a single figure.<\/span><\/div>tiledlayout(2,2)<\/span><\/span><\/div><\/div>nexttile<\/span><\/span><\/div><\/div>plotLabColormapWithGamutAlarm(lab)<\/span><\/span><\/div><\/div><\/div><\/div>nexttile<\/span><\/span><\/div><\/div>plotLabRGBColorsWithGamutAlarm(lab)<\/span><\/span><\/div><\/div>title(<\/span>\"RGB values\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div>nexttile<\/span><\/span><\/div><\/div>plotABWithGamutAlarm(lab)<\/span><\/span><\/div><\/div>title(<\/span>\"a-b values\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div>nexttile<\/span><\/span><\/div><\/div>plotLWithGamutAlarm(lab)<\/span><\/span><\/div><\/div>title(<\/span>\"L values\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div><\/div><\/div>Utility Functions<\/span><\/h4>function <\/span>plotLabColormapWithGamutAlarm(lab)<\/span><\/span><\/div><\/div><\/div><\/div>[first,last] = outOfGamutSegments(lab);<\/span><\/span><\/div><\/div><\/div><\/div>rgb = lab2rgb(lab);<\/span><\/span><\/div><\/div>ax = newplot;<\/span><\/span><\/div><\/div><\/div><\/div>colorSwatches(ax,rgb,0)<\/span><\/span><\/div><\/div>daspect(ax,[30 1 1])<\/span><\/span><\/div><\/div>xlim(ax,[0 size(lab,1)])<\/span><\/span><\/div><\/div>ylim(ax,[0 1.5])<\/span><\/span><\/div><\/div>axis(ax,<\/span>\"off\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div>hold(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>y = [1.25 1.25];<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    x1 = first(k) - 1;<\/span><\/span><\/div><\/div>    x2 = last(k);<\/span><\/span><\/div><\/div>    x = [x1 x2];<\/span><\/span><\/div><\/div>    plot(ax,x,y,<\/span>'r'<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold(ax,<\/span>\"off\"<\/span>)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>function <\/span>plotLabRGBColorsWithGamutAlarm(lab)<\/span><\/span><\/div><\/div><\/div><\/div>ax = newplot;<\/span><\/span><\/div><\/div>rgb = lab2rgb(lab);<\/span><\/span><\/div><\/div>hold(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>plot(ax,rgb(:,1),<\/span>'r'<\/span>)<\/span><\/span><\/div><\/div>plot(ax,rgb(:,2),<\/span>'g'<\/span>)<\/span><\/span><\/div><\/div>plot(ax,rgb(:,3),<\/span>'b'<\/span>)<\/span><\/span><\/div><\/div>xlim(ax,[1 - 0.05*height(rgb), 1.05*height(rgb)]);<\/span><\/span><\/div><\/div>y1 = min(-0.2,ax.YLim(1));<\/span><\/span><\/div><\/div>y2 = max(1.2,ax.YLim(2));<\/span><\/span><\/div><\/div>ylim(ax,[y1 y2]);<\/span><\/span><\/div><\/div>grid(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>yline(ax,0, LineWidth = 5, Color = [0.7 0.7 0.7])<\/span><\/span><\/div><\/div>yline(ax,1, LineWidth = 5, Color = [0.7 0.7 0.7])<\/span><\/span><\/div><\/div><\/div><\/div>too_high = any(rgb > 1,2);<\/span><\/span><\/div><\/div>k = find(too_high);<\/span><\/span><\/div><\/div>if <\/span>~isempty(k)<\/span><\/span><\/div><\/div>    plot(ax,k,ones(size(k)),<\/span>'r*'<\/span>,MarkerSize = 6)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>too_low = any(rgb < 0,2);<\/span><\/span><\/div><\/div>k = find(too_low);<\/span><\/span><\/div><\/div>if <\/span>~isempty(k)<\/span><\/span><\/div><\/div>    plot(ax,k,zeros(size(k)),<\/span>'r*'<\/span>,MarkerSize = 6)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold(ax,<\/span>\"off\"<\/span>)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>function <\/span>plotABWithGamutAlarm(lab)<\/span><\/span><\/div><\/div><\/div><\/div>ax = newplot;<\/span><\/span><\/div><\/div>plot(ax,lab(:,2),lab(:,3));<\/span><\/span><\/div><\/div>axis(ax,<\/span>\"equal\"<\/span>)<\/span><\/span><\/div><\/div>xlim(ax,[-110 110])<\/span><\/span><\/div><\/div>ylim(ax,[-110 110])<\/span><\/span><\/div><\/div>ax.XAxisLocation = <\/span>\"origin\"<\/span>;<\/span><\/span><\/div><\/div>ax.YAxisLocation = <\/span>\"origin\"<\/span>;<\/span><\/span><\/div><\/div>xlabel(<\/span>\"a\"<\/span>)<\/span><\/span><\/div><\/div>ylabel(<\/span>\"b\"<\/span>)<\/span><\/span><\/div><\/div><\/div><\/div>[first,last] = outOfGamutSegments(lab);<\/span><\/span><\/div><\/div><\/div><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    j1 = first(k);<\/span><\/span><\/div><\/div>    j2 = last(k);<\/span><\/span><\/div><\/div>    x = lab(j1:j2,2);<\/span><\/span><\/div><\/div>    y = lab(j1:j2,3);<\/span><\/span><\/div><\/div>    plot(ax,x,y,<\/span>'r'<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold <\/span>off<\/span><\/span><\/div><\/div><\/div><\/div>grid(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>function <\/span>plotLWithGamutAlarm(lab)<\/span><\/span><\/div><\/div><\/div><\/div>ax = newplot;<\/span><\/span><\/div><\/div>plot(ax,lab(:,1));<\/span><\/span><\/div><\/div>xlim(ax,[1 - 0.05*height(lab), 1.05*height(lab)]);<\/span><\/span><\/div><\/div>ylim(ax,[-10 110])<\/span><\/span><\/div><\/div><\/div><\/div>[first,last] = outOfGamutSegments(lab);<\/span><\/span><\/div><\/div><\/div><\/div>hold <\/span>on<\/span><\/span><\/div><\/div>for <\/span>k = 1:length(first)<\/span><\/span><\/div><\/div>    j1 = first(k);<\/span><\/span><\/div><\/div>    j2 = last(k);<\/span><\/span><\/div><\/div>    x = j1:j2;<\/span><\/span><\/div><\/div>    y = lab(j1:j2,1);<\/span><\/span><\/div><\/div>    plot(ax,x,y,<\/span>'r'<\/span>,LineWidth = 5)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div>hold <\/span>off<\/span><\/span><\/div><\/div><\/div><\/div>grid(ax,<\/span>\"on\"<\/span>)<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>function <\/span>[first,last] = outOfGamutSegments(lab)<\/span><\/span><\/div><\/div><\/div><\/div>rgb = lab2rgb(lab);<\/span><\/span><\/div><\/div><\/div><\/div>out_of_gamut_mask = any(rgb > 1,2) | any(rgb < 0,2);<\/span><\/span><\/div><\/div>d = diff([0 ; out_of_gamut_mask ; 0]);<\/span><\/span><\/div><\/div>first = find(d == 1);<\/span><\/span><\/div><\/div>last = find(d == -1) - 1;<\/span><\/span><\/div><\/div>end<\/span><\/span><\/div><\/div><\/div><\/div>\r\n