function writepng(data, map, filename, varargin)

%WRITEPNG Write a PNG file to disk.

%   WRITEPNG(I,[],FILENAME) writes the grayscale image I

%   to the file specified by the string FILENAME.

%

%   WRITEPNG(RGB,[],FILENAME) writes the truecolor image

%   represented by the M-by-N-by-3 array RGB.

%

%   WRITEPNG(X,MAP,FILENAME) writes the indexed image X with

%   colormap MAP.  The resulting file will contain the equivalent

%   truecolor image.

%

%   WRITEPNG(...,PARAM,VAL,...) sets the specified parameters.

%

%   See also IMREAD, IMWRITE, IMFINFO.

%   Copyright 1984-2018 The MathWorks, Inc.

% Parse the inputs 

[results, unmatched] = parseInputs(data,map,filename,varargin{:}); 

if ((ndims(data) > 3) || (~ismember(size(data,3), [1 3]))) 

    error(message('MATLAB:imagesci:writepng:wrongImageDimensions'));

end 

alpha = results.alpha; 

% Identify color type

isTruecolor = (size(data,3) == 3); 

paletteUsed = ~isempty(map) && ~isTruecolor; 

colorUsed = paletteUsed || isTruecolor; 

alphaUsed = ~isempty(alpha); 

colortype = paletteUsed + 2*colorUsed + 4*alphaUsed; 

if (colortype == 7) 

    error(message('MATLAB:imagesci:writepng:alphaNotSupportedForIndexed'));

end 

% Set default bitdepth if not specified

bitdepth = results.bitdepth; 

if (isempty(bitdepth)) 

    switch class(data) 

        case 'logical' 

            bitdepth = 1;

        case {'uint8', 'double', 'single'} 

            bitdepth = 8; 

        case 'uint16'

            bitdepth = 16;

    end 

end 

% Color type values (as in PNG library defs)

PNG_COLOR_TYPE_GRAY = 0; 

PNG_COLOR_TYPE_RGB = 2; 

PNG_COLOR_TYPE_PALETTE = 3; 

PNG_COLOR_TYPE_GRAY_ALPHA = 4; 

PNG_COLOR_TYPE_RGB_ALPHA = 6; 

% Validate bitdepth

switch colortype 

    case PNG_COLOR_TYPE_GRAY 

        if (~ismember(bitdepth, [1 2 4 8 16]))

            error(message('MATLAB:imagesci:writepng:invalidGrayscaleBitDepth'));

        end

    case { PNG_COLOR_TYPE_RGB, PNG_COLOR_TYPE_RGB_ALPHA } 

        if (~ismember(bitdepth, [8 16])) 

            error(message('MATLAB:imagesci:writepng:invalidRgbBitDepth'));

        end 

    case PNG_COLOR_TYPE_PALETTE

        if (~ismember(bitdepth, [1 2 4 8]))

            error(message('MATLAB:imagesci:writepng:invalidIndexedBitDepth'));

        end

    case PNG_COLOR_TYPE_GRAY_ALPHA

        if (~ismember(bitdepth, [8 16]))

            error(message('MATLAB:imagesci:writepng:invalidGrayscaleAlphaBitDepth'));

        end

end 

%

% Scale image if necessary to match requested bitdepth

%

switch class(data) 

    case {'double', 'single'} 

        if (colortype == PNG_COLOR_TYPE_PALETTE)

            data = data - 1;

            data = uint8(data);

        else

            % Grayscale or RGB; clamp data to [0,1] dynamic range before

            % scaling, rounding, and casting.

            data = max(min(data,1),0);

            switch bitdepth

                case 8

                    data = uint8(255*data);

                case 16

                    data = uint16(65535*data);

                case 4

                    data = uint8(15*data);

                case 2

                    data = uint8(3*data);

                case 1

                    data = uint8(data ~= 0);

            end

        end

    case 'uint8' 

        if (colortype == PNG_COLOR_TYPE_PALETTE) 

            % Nothing to do

        else 

            switch bitdepth 

                case 16 

                    data = uint16(data);

                    data = bitor(bitshift(data,8),data);

                case 8 

                    % Nothing to do

                case 4

                    data = bitshift(data,-4);

                case 2

                    data = bitshift(data,-6);

                case 1

                    % Nothing to do

            end 

        end 

    case 'uint16'

        switch bitdepth

            case 16

                % Nothing to do

            case 8

                data = uint8(bitshift(data,-8));

            case 4

                data = uint8(bitshift(data,-12));

            case 2

                data = uint8(bitshift(data,-14));

            case 1

                data = uint8(data ~= 0);

        end

end 

if (ismember(colortype, [PNG_COLOR_TYPE_GRAY_ALPHA, ... 

        PNG_COLOR_TYPE_RGB_ALPHA])) 

    %

    % Scale alpha data if necessary to match data class

    %

    switch bitdepth

        case 8

            switch class(alpha)

                case {'double', 'single'}

                    alpha = max(min(alpha,1),0);

                    alpha = uint8(255 * alpha);

                case 'uint16'

                    alpha = uint8(bitshift(alpha, -8));

                case 'uint8'

                    % nothing to do

            end

        case 16

            switch class(alpha)

                case {'double', 'single'}

                    alpha = max(min(alpha,1),0);

                    alpha = uint16(65535 * alpha);

                case 'uint16'

                    % nothing to do

                case 'uint8'

                    alpha = uint16(alpha);

                    alpha = bitor(bitshift(alpha, 8), alpha);

            end

    end

end 

sigbits        = results.significantbits; 

transparency   = results.transparency; 

background     = results.background; 

gamma          = results.gamma; 

chromaticities = results.chromaticities; 

xres           = results.xresolution; 

yres           = results.yresolution; 

if ischar(results.resolutionunit) 

    resunit        = validatestring(results.resolutionunit,{'unknown','meter'}); 

else

    resunit = results.resolutionunit;

end 

interlace      = validatestring(results.interlacetype,{'none','adam7'}); 

imagemodtime   = results.imagemodtime; 

textchunks = cell(0,2); 

strs = {'Title','Author','Description','Copyright','Software', ... 

    'Disclaimer', 'Warning','Source','Comment'};

for j = 1:numel(strs) 

    param_name = lower(strs{j}); 

    if isfield(results,lower(param_name)) 

        param_value = results.(param_name); 

        if ~isempty(param_value) 

            textchunks{end+1,1} = strs{j}; %#ok<AGROW> 

            textItem = CheckTextItem(param_value); 

            textchunks{end,2} = textItem; 

        end 

    end 

end 

if ~isempty(results.creationtime) 

    keyword = 'Creation Time'; 

    ctime = results.creationtime; 

    if ischar(ctime) 

        textItem = datestr(datenum(ctime), 0); 

    else

        textItem = datestr(ctime, 0);

    end 

    textchunks{end+1,1} = keyword; 

    textchunks{end,2} = textItem; 

end 

if ~isempty(results.imagemodtime) 

    try

        imagemodtime = fix(datevec(results.imagemodtime));

    catch me

        error(message('MATLAB:imagesci:writepng:invalidImageModTime'));

    end

    if (numel(imagemodtime) > 6)

        error(message('MATLAB:imagesci:writepng:tooMuchImageModTimeData'))

    end

end 

% validate and process any unmatched parameters.

if ~isempty(unmatched) 

    param_names = fields(unmatched); 

    nelts = numel(param_names); 

    for j = 1:nelts 

        param_name = param_names{j};

        keyword = CheckKeyword(param_name);

        item = CheckTextItem(unmatched.(param_name));

        textchunks{end+1,1} = keyword; %#ok<AGROW>

        textchunks{end,2} = item;

    end

end 

% Be friendly about specifying resolutions

if (~isempty(xres) && isempty(yres)) 

    yres = xres;

elseif (~isempty(yres) && isempty(xres)) 

    xres = yres;

end 

if (~isempty(xres) && isempty(resunit)) 

    resunit = 'unknown';

end 

if (isempty(xres) && isempty(yres) && ~isempty(resunit)) 

    error(message('MATLAB:imagesci:writepng:resolutionsRequired'));

end 

pngwritec(data, map, filename, colortype, bitdepth, ... 

    sigbits, alpha, interlace, ... 

    transparency, background, gamma, ... 

    chromaticities, xres, yres, ... 

    resunit, textchunks, imagemodtime);