Shade/color matching of the input image with reference shade chart

Question

Kumar 2014-1-5

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https://ww2.mathworks.cn/matlabcentral/answers/111477-shade-color-matching-of-the-input-image-with-reference-shade-chart

评论： Walter Roberson 2018-2-8

Dear Friends,

I have to segment different shades of colour from an image. There is name for each reference color. I have utlisied many suggested methods here like colorlab/edge detection etc. But they did not work as my color of interest is all white based and closer (in colour) to each other.

I am looking for a method to match the image with reference shade as in the figure below.

Please someone help me

Thanks in advance.

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Answer 1

Image Analyst 2014-1-5

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https://ww2.mathworks.cn/matlabcentral/answers/111477-shade-color-matching-of-the-input-image-with-reference-shade-chart#answer_120081

You need to calculate the color difference. See lengthy discussions I had with this poster who wanted to match grass to standard colored tiles. http://www.mathworks.com/matlabcentral/answers/contributors/3595115-elvin/questions

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Kumar 2014-1-6

编辑：Kumar 2014-1-6

在 MATLAB Online 中打开

Thanks again. Now I am getting dimensional error. I tried to implement your methedology of deltaE.It turns dimensional error.

Please forgive me if I am foolish.

I read image using imread and then tried to convert into Lab colourspace using your deltaE example. but getting error:

>> fullImageFileName = 'teeth.jpg';
>> % Read in image into an array.
  [rgbImage storedColorMap] = imread(fullImageFileName); 
  [rows columns numberOfColorBands] = size(rgbImage); 
  % If it's monochrome (indexed), convert it to color. 
  % Check to see if it's an 8-bit image needed later for scaling).
  if strcmpi(class(rgbImage), 'uint8')
    % Flag for 256 gray levels.
    eightBit = true;
  else
    eightBit = false;
  end
  if numberOfColorBands == 1
    if isempty(storedColorMap)
      % Just a simple gray level image, not indexed with a stored color map.
      % Create a 3D true color image where we copy the monochrome image into all 3 (R, G, & B) color planes.
      rgbImage = cat(3, rgbImage, rgbImage, rgbImage);
    else
      % It's an indexed image.
      rgbImage = ind2rgb(rgbImage, storedColorMap);
      % ind2rgb() will convert it to double and normalize it to the range 0-1.
      % Convert back to uint8 in the range 0-255, if needed.
      if eightBit
        rgbImage = uint8(255 * rgbImage);
      end
    end
  end
  
  % Display the original image.
  h1 = subplot(3, 4, 1);
  imshow(rgbImage);
  drawnow; % Make it display immediately. 
  if numberOfColorBands > 1 
    title('Original Color Image', 'FontSize', fontSize); 
  else 
    caption = sprintf('Original Indexed Image\n(converted to true color with its stored colormap)');
    title(caption, 'FontSize', fontSize);
  end
Undefined function or variable 'fontSize'.
>> cform = makecform('srgb2lab');
  lab_Image = applycform(im2double(rgbImage),cform);
  
  % Extract out the color bands from the original image
  % into 3 separate 2D arrays, one for each color component.
  LChannel = lab_Image(:, :, 1); 
  aChannel = lab_Image(:, :, 2); 
  bChannel = lab_Image(:, :, 3); 
>> % Display the lab images.
  subplot(3, 4, 2);
  imshow(LChannel, []);
  title('L Channel', 'FontSize', fontSize);
  subplot(3, 4, 3);
  imshow(aChannel, []);
  title('a Channel', 'FontSize', fontSize);
  subplot(3, 4, 4);
  imshow(bChannel, []);
  title('b Channel', 'FontSize', fontSize);
  % Get the average lab color value.
  [LMean, aMean, bMean] = GetMeanLABValues(LChannel, aChannel, bChannel, mask);
Undefined function or variable 'fontSize'.
>>  LStandard = [82.56,78.43,74.44,73.68];
    aStandard = [1.37,3.82,4.02,5.41];
    bStandard = [12.33,21.35,20.23,23.09];
  
  
  % Create the delta images: delta L, delta A, and delta B.
  deltaL = LChannel - LStandard;
  deltaa = aChannel - aStandard;
  deltab = bChannel - bStandard;
  
  % Create the Delta E image.
  % This is an image that represents the color difference.
  % Delta E is the square root of the sum of the squares of the delta images.
  deltaE = sqrt(deltaL .^ 2 + deltaa .^ 2 + deltab .^ 2);
  
  % Mask it to get the Delta E in the mask region only.
  maskedDeltaE = deltaE .* mask;
  % Get the mean delta E in the mask region
  % Note: deltaE(mask) is a 1D vector of ONLY the pixel values within the masked area.
   meanMaskedDeltaE = mean(deltaE(mask));
  % Get the standard deviation of the delta E in the mask region
  stDevMaskedDeltaE = std(deltaE(mask));
  message = sprintf('The mean LAB = (%.2f, %.2f, %.2f).\nThe mean Delta E in the masked region is %.2f +/- %.2f',...
    LMean, aMean, bMean, meanMaskedDeltaE, stDevMaskedDeltaE);  
  
  % Display the masked Delta E image - the delta E within the masked region only.
  subplot(3, 4, 6);
  imshow(maskedDeltaE, []);
  caption = sprintf('Delta E between image within masked region\nand mean color within masked region.\n(With amplified intensity)');
  title(caption, 'FontSize', fontSize);
  % Display the Delta E image - the delta E over the entire image.
  subplot(3, 4, 7);
  imshow(deltaE, []);
  caption = sprintf('Delta E Image\n(Darker = Better Match)');
  title(caption, 'FontSize', fontSize);
  % Plot the histograms of the Delta E color difference image,
  % both within the masked region, and for the entire image.
  PlotHistogram(deltaE(mask), deltaE, [3 4 8], 'Histograms of the 2 Delta E Images');
  
  message = sprintf('%s\n\nRegions close in color to the color you picked\nwill be dark in the Delta E image.\n', message);
  msgboxw(message);
  % Find out how close the user wants to match the colors.
  prompt = {sprintf('First, examine the histogram.\nThen find pixels within this Delta E (from the average color in the region you drew):')};
  dialogTitle = 'Enter Delta E Tolerance';
  numberOfLines = 1;
  % Set the default tolerance to be the mean delta E in the masked region plus two standard deviations.
  strTolerance = sprintf('%.1f', meanMaskedDeltaE + 3 * stDevMaskedDeltaE);
  defaultAnswer = {strTolerance};  % Suggest this number to the user.
  response = inputdlg(prompt, dialogTitle, numberOfLines, defaultAnswer);
  % Update tolerance with user's response.
  tolerance = str2double(cell2mat(response));
  % Let them interactively select the threshold with the threshold() m-file.
  % (Note: This is a separate function in a separate file in my File Exchange.)
%   threshold(deltaE);
  
  % Place a vertical bar at the threshold location.
  handleToSubPlot8 = subplot(3, 4, 8);  % Get the handle to the plot.
  PlaceVerticalBarOnPlot(handleToSubPlot8, tolerance, [0 .5 0]);  % Put a vertical red line there.
  
  % Find pixels within that delta E.
  binaryImage = deltaE <= tolerance;
  subplot(3, 4, 9);
  imshow(binaryImage, []);
  title('Matching Colors Mask', 'FontSize', fontSize);
  
  % Mask the image with the matching colors and extract those pixels.
  matchingColors = bsxfun(@times, rgbImage, cast(binaryImage, class(rgbImage)));
  subplot(3, 4, 10);
  imshow(matchingColors);
  caption = sprintf('Matching Colors (Delta E <= %.1f)', tolerance);
  title(caption, 'FontSize', fontSize);
  % Mask the image with the NON-matching colors and extract those pixels.
  nonMatchingColors = bsxfun(@times, rgbImage, cast(~binaryImage, class(rgbImage)));
  subplot(3, 4, 11);
  imshow(nonMatchingColors);
  caption = sprintf('Non-Matching Colors (Delta E > %.1f)', tolerance);
  title(caption, 'FontSize', fontSize);
  % Display credits: the MATLAB logo and my name.
  ShowCredits(); % Display logo in plot position #12.
  
  % Alert user that the demo has finished.
  message = sprintf('Done!\n\nThe demo has finished.\nRegions close in color to the color you picked\nwill be dark in the Delta E image.\n');
  msgbox(message);
  
catch ME
  errorMessage = sprintf('Error running this m-file:\n%s\n\nThe error message is:\n%s', ...
    mfilename('fullpath'), ME.message);
  errordlg(errorMessage);
end
return; % from SimpleColorDetection()
% ---------- End of main function ---------------------------------
%----------------------------------------------------------------------------
% Display the MATLAB logo.
function ShowCredits()
try
%   xpklein;
%   surf(peaks(30));
  logoFig = subplot(3, 4, 12);
  caption = sprintf('A MATLAB Demo\nby ImageAnalyst');
  text(0.5,1.15, caption, 'Color','r', 'FontSize', 18, 'FontWeight','b', 'HorizontalAlignment', 'Center') ;
  positionOfLowerRightPlot = get(logoFig, 'position');
  L = 40*membrane(1,25);
  logoax = axes('CameraPosition', [-193.4013 -265.1546  220.4819],...
    'CameraTarget',[26 26 10], ...
    'CameraUpVector',[0 0 1], ...
    'CameraViewAngle',9.5, ...
    'DataAspectRatio', [1 1 .9],...
    'Position', positionOfLowerRightPlot, ...
    'Visible','off', ...
    'XLim',[1 51], ...
    'YLim',[1 51], ...
    'ZLim',[-13 40], ...
    'parent',gcf);
  s = surface(L, ...
    'EdgeColor','none', ...
    'FaceColor',[0.9 0.2 0.2], ...
    'FaceLighting','phong', ...
    'AmbientStrength',0.3, ...
    'DiffuseStrength',0.6, ... 
    'Clipping','off',...
    'BackFaceLighting','lit', ...
    'SpecularStrength',1.1, ...
    'SpecularColorReflectance',1, ...
    'SpecularExponent',7, ...
    'Tag','TheMathWorksLogo', ...
    'parent',logoax);
  l1 = light('Position',[40 100 20], ...
    'Style','local', ...
    'Color',[0 0.8 0.8], ...
    'parent',logoax);
  l2 = light('Position',[.5 -1 .4], ...
    'Color',[0.8 0.8 0], ...
    'parent',logoax);
catch ME
  errorMessage = sprintf('Error running ShowCredits().\n\nThe error message is:\n%s', ...
    ME.message);
  errordlg(errorMessage);
end
return; % from ShowCredits()
%-----------------------------------------------------------------------------
function [xCoords, yCoords, roiPosition] = DrawBoxRegion(handleToImage)
  try
  % Open a temporary full-screen figure if requested.
  enlargeForDrawing = true;
  axes(handleToImage);
  if enlargeForDrawing
    hImage = findobj(gca,'Type','image');
    numberOfImagesInside = length(hImage);
    if numberOfImagesInside > 1
      imageInside = get(hImage(1), 'CData');
    else
      imageInside = get(hImage, 'CData');
    end
    hTemp = figure;
    hImage2 = imshow(imageInside, []);
    [rows columns NumberOfColorBands] = size(imageInside);
    set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
  end
  
  txtInfo = sprintf('Draw a box over the unstained fabric by clicking and dragging over the image.\nDouble click inside the box to finish drawing.');
  text(10, 40, txtInfo, 'color', 'r', 'FontSize', 24);
      % Prompt user to draw a region on the image.
    msgboxw(txtInfo);
    
    % Erase all previous lines.
    if ~enlargeForDrawing
      axes(handleToImage);
  %     ClearLinesFromAxes(handles);
    end
    
    hBox = imrect;
    roiPosition = wait(hBox);
    roiPosition
    % Erase all previous lines.
    if ~enlargeForDrawing
      axes(handleToImage);
  %     ClearLinesFromAxes(handles);
    end
  xCoords = [roiPosition(1), roiPosition(1)+roiPosition(3), roiPosition(1)+roiPosition(3), roiPosition(1), roiPosition(1)];
  yCoords = [roiPosition(2), roiPosition(2), roiPosition(2)+roiPosition(4), roiPosition(2)+roiPosition(4), roiPosition(2)];
  % Plot the mask as an outline over the image.
  hold on;
  plot(xCoords, yCoords, 'linewidth', 2);
  close(hTemp);
  catch ME
    errorMessage = sprintf('Error running DrawRegion:\n\n\nThe error message is:\n%s', ...
      ME.message);
    WarnUser(errorMessage);
  end
  return; % from DrawRegion
  
%-----------------------------------------------------------------------------
function [mask] = DrawFreehandRegion(handleToImage, rgbImage)
try
  fontSize = 14;
  % Open a temporary full-screen figure if requested.
  enlargeForDrawing = true;
  axes(handleToImage);
  if enlargeForDrawing
    hImage = findobj(gca,'Type','image');
    numberOfImagesInside = length(hImage);
    if numberOfImagesInside > 1
      imageInside = get(hImage(1), 'CData');
    else
      imageInside = get(hImage, 'CData');
    end
    hTemp = figure;
    hImage2 = imshow(imageInside, []);
    [rows columns NumberOfColorBands] = size(imageInside);
    set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
  end
  
  message = sprintf('Left click and hold to begin drawing.\nSimply lift the mouse button to finish');
  text(10, 40, message, 'color', 'r', 'FontSize', fontSize);
      % Prompt user to draw a region on the image.
    uiwait(msgbox(message));
    
    % Now, finally, have the user freehand draw the mask in the image.
    hFH = imfreehand();
  % Once we get here, the user has finished drawing the region.
  % Create a binary image ("mask") from the ROI object.
  mask = hFH.createMask();
  
  % Close the maximized figure because we're done with it.
  close(hTemp);
  % Display the freehand mask.
  subplot(3, 4, 5);
  imshow(mask);
  title('Binary mask of the region', 'FontSize', fontSize);
  
  % Mask the image.
  maskedRgbImage = bsxfun(@times, rgbImage, cast(mask,class(rgbImage)));
  % Display it.
  subplot(3, 4, 6);
  imshow(maskedRgbImage);
catch ME
  errorMessage = sprintf('Error running DrawFreehandRegion:\n\n\nThe error message is:\n%s', ...
    ME.message);
  WarnUser(errorMessage);
end
return; % from DrawFreehandRegion
%-----------------------------------------------------------------------------
% Get the average lab within the mask region.
function [LMean, aMean, bMean] = GetMeanLABValues(LChannel, aChannel, bChannel, mask)
try
  LVector = LChannel(mask); % 1D vector of only the pixels within the masked area.
  LMean = mean(LVector);
  aVector = aChannel(mask); % 1D vector of only the pixels within the masked area.
  aMean = mean(aVector);
  bVector = bChannel(mask); % 1D vector of only the pixels within the masked area.
  bMean = mean(bVector);
catch ME
  errorMessage = sprintf('Error running GetMeanLABValues:\n\n\nThe error message is:\n%s', ...
    ME.message);
  WarnUser(errorMessage);
end
return; % from GetMeanLABValues
%==========================================================================================================================
function WarnUser(warningMessage)
  uiwait(warndlg(warningMessage));
  return; % from WarnUser()
  
%==========================================================================================================================
function msgboxw(message)
  uiwait(msgbox(message));
  return; % from msgboxw()
  
%==========================================================================================================================
% Plots the histograms of the pixels in both the masked region and the entire image.
function PlotHistogram(maskedRegion, doubleImage, plotNumber, caption)
try
  fontSize = 14;
  subplot(plotNumber(1), plotNumber(2), plotNumber(3)); 
  % Find out where the edges of the histogram bins should be.
  maxValue1 = max(maskedRegion(:));
  maxValue2 = max(doubleImage(:));
  maxOverallValue = max([maxValue1 maxValue2]);
  edges = linspace(0, maxOverallValue, 100);
  % Get the histogram of the masked region into 100 bins.
  pixelCount1 = histc(maskedRegion(:), edges);
  % Get the histogram of the entire image into 100 bins.
  pixelCount2 = histc(doubleImage(:), edges);
  % Plot the  histogram of the entire image.
  plot(edges, pixelCount2, 'b-');
  
  % Now plot the histogram of the masked region.
  % However there will likely be so few pixels that this plot will be so low and flat compared to the histogram of the entire
  % image that you probably won't be able to see it.  To get around this, let's scale it to make it higher so we can see it.
  gainFactor = 1.0;
  maxValue3 = max(max(pixelCount2));
  pixelCount3 = gainFactor * maxValue3 * pixelCount1 / max(pixelCount1);
  hold on;
  plot(edges, pixelCount3, 'r-');
  title(caption, 'FontSize', fontSize);
  
  % Scale x axis manually.
  xlim([0 edges(end)]);
  legend('Entire', 'Masked');
  
catch ME
  errorMessage = sprintf('Error running PlotHistogram:\n\n\nThe error message is:\n%s', ...
    ME.message);
  WarnUser(errorMessage);
end
return; % from PlotHistogram
%=====================================================================
% Shows vertical lines going up from the X axis to the curve on the plot.
function lineHandle = PlaceVerticalBarOnPlot(handleToPlot, x, lineColor)
  try
    % If the plot is visible, plot the line.
    if get(handleToPlot, 'visible')
      axes(handleToPlot);  % makes existing axes handles.axesPlot the current axes.
      % Make sure x location is in the valid range along the horizontal X axis.
      XRange = get(handleToPlot, 'XLim');
      maxXValue = XRange(2);
      if x > maxXValue
        x = maxXValue;
      end
      % Erase the old line.
      %hOldBar=findobj('type', 'hggroup');
      %delete(hOldBar);
      % Draw a vertical line at the X location.
      hold on;
      yLimits = ylim;
      lineHandle = line([x x], [yLimits(1) yLimits(2)], 'Color', lineColor, 'LineWidth', 3);
      hold off;
    end
  catch ME
    errorMessage = sprintf('Error running PlaceVerticalBarOnPlot:\n\n\nThe error message is:\n%s', ...
      ME.message);
    WarnUser(errorMessage);
end
  return;  % End of PlaceVerticalBarOnPlot
Error using  - 
Matrix dimensions must agree.
>>

Kumar 2014-1-6

在 MATLAB Online 中打开

Thanks still it returns error. I simplified further through to understand the basic. It gives me too many error:

imread('teeth.jpg')
%load rgb image
src = 'teeth.jpg';
rgbI = imread(src);
%convert to lab
labTransformation = makecform('srgb2lab');
labI = applycform(rgbI,labTransformation);
%seperate l,a,b
l = labI(:,:,1);
a = labI(:,:,2);
b = labI(:,:,3);
figure, imshow(l) , title('l');
figure, imshow(a) , title('a');
figure, imshow(b) , title('b');
 LStandard = [82.56,78.43,74.44,73.68];
 aStandard = [1.37,3.82,4.02,5.41];
 bStandard = [12.33,21.35,20.23,23.09];
  
  
  % Create the delta images: delta L, delta A, and delta B.
  deltaL = l - LStandard;
  deltaa = a - aStandard;
  deltab = b - bStandard;
  
  % Create the Delta E image.
  % This is an image that represents the color difference.
  % Delta E is the square root of the sum of the squares of the delta images.
  deltaE = sqrt(deltaL .^ 2 + deltaa .^ 2 + deltab .^ 2);
    figure, imshow(deltaE)

This gives me error like:

Error using - Integers can only be combined with integers of the same class, or scalar doubles.

Error in Untitled2 (line 24) deltaL = l - LStandard;

Image Analyst 2018-2-8

You forgot to attach 'C:\Users\user\Desktop\FYP pic\Single teeth.JPG'

Walter Roberson 2018-2-8

Addressed in https://www.mathworks.com/matlabcentral/answers/381436-code-error-of-shade-matching-image-processing

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Shade/color matching of the input image with reference shade chart

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Shade/color matching of the input image with reference shade chart

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