function u = im2uint8(varargin)

%IM2UINT8 Convert image to 8-bit unsigned integers.

%   IM2UINT8 takes an image as input, and returns an image of class uint8.  If

%   the input image is of class uint8, the output image is identical to it.  If

%   the input image is not uint8, IM2UINT8 returns the equivalent image of class

%   uint8, rescaling or offsetting the data as necessary.

%

%   I2 = IM2UINT8(I1) converts the intensity image I1 to uint8, rescaling the

%   data if necessary.

%

%   RGB2 = IM2UINT8(RGB1) converts the truecolor image RGB1 to uint8, rescaling

%   the data if necessary.

%

%   I = IM2UINT8(BW) converts the binary image BW to a uint8 intensity image,

%   changing one-valued elements to 255.

%

%   X2 = IM2UINT8(X1,'indexed') converts the indexed image X1 to uint8,

%   offsetting the data if necessary. Note that it is not always possible to

%   convert an indexed image to uint8. If X1 is double, then the maximum value

%   of X1 must be 256 or less.  If X1 is uint16, the maximum value of X1 must be

%   255 or less.

%

%   Class Support

%   -------------

%   Intensity and truecolor images can be uint8, uint16, double, logical,

%   single, or int16. Indexed images can be uint8, uint16, double or

%   logical. Binary input images must be logical. The output image is uint8.

%

%   Example

%   -------

%       I1 = reshape(uint16(linspace(0,65535,25)),[5 5])

%       I2 = im2uint8(I1)

%

%   See also IM2DOUBLE, IM2INT16, IM2SINGLE, IM2UINT16, UINT8.

%   Copyright 1993-2004 The MathWorks, Inc.

%   $Revision: 1.20.4.5 $  $Date: 2005/11/15 00:58:23 $

iptchecknargin(1,2,nargin,mfilename);

img = varargin{1};

iptcheckinput(img,{'double','logical','uint8','uint16','single','int16'}, ...

              {'nonsparse'},mfilename,'Image',1);

if nargin == 2

  typestr = varargin{2};

  iptcheckstrs(typestr,{'indexed'},mfilename,'type',2);

end

% 如果图像类型为uint8,则不改变

if isa(img, 'uint8')

    u = img; 

% 如果图像类型为logical(二值),则将1转为255和0仍然为0

elseif isa(img, 'logical')

    u=uint8(img);

    u(img)=255;

else %double, single, uint16, or int16

  if nargin == 1        %输入参数个数为1

    if isa(img, 'int16')    %如果图像类型为int16,则将其转为int16--这是因为grayto8函数不支持int16

      img = int16touint16(img);

    end

    % intensity image; call MEX-file

    u = grayto8(img);

  else        %输入参数个数为2

    if isa(img, 'int16')

      eid = sprintf('Images:%s:invalidIndexedImage',mfilename);

      msg1 = 'An indexed image can be uint8, uint16, double, single, or ';

      msg2 = 'logical.';

      error(eid,'%s %s',msg1, msg2);

    elseif isa(img, 'uint16')

      if (max(img(:)) > 255)

        msg = 'Too many colors for 8-bit integer storage.';

        eid = sprintf('Images:%s:tooManyColorsFor8bitStorage',mfilename);

        error(eid,msg);

      else

        u = uint8(img);

      end

    else %double or single   值范围1-256

      if max(img(:)) >= 257

        msg = 'Too many colors for 8-bit integer storage.';

        eid = sprintf('Images:%s:tooManyColorsFor8bitStorage',mfilename);

        error(eid,msg);

      elseif min(img(:)) < 1

        msg = 'Invalid indexed image: an index was less than 1.';

        eid = sprintf('Images:%s:invalidIndexedImage',mfilename);

        error(eid,msg);

      else

        u = uint8(img-1);

      end

    end

  end

end

/*

 * GRAYTO8 MEX-file

 *

 * B = GRAYTO8(A) converts the double array A to uint8 by scaling A by 255

 * and then rounding.  NaN's in A are converted to 0.  Values in A greater

 * than 1.0 are converted to 255; values less than 0.0 are converted to 0.

 *

 * B = GRAYTO8(A) converts the uint16 array A by scaling the elements of A

 * 255/65535, rounding, and then casting to uint8.

 *

 * Copyright 1993-2007 The MathWorks, Inc.

 *

 */

#include "mex.h"

#include "math.h"

#include "mwsize.h"

// double类型转换

void ConvertFromDouble(double *pr, uint8_T *qr, mwSize numElements) {

    mwSize k;

    double val;

    for (k = ; k < numElements; k++) {

        val = *pr++;

        if (mxIsNaN(val)) {

            *qr++ = ;

        }

        else {

            val = val * 255.0 + 0.5;    // 数据加0.5是为了四舍五入需要 例如 uint8(245.1+0.5)=245 和 uint8(245.6+0.5)=246

            if (val > 255.0) val = 255.0;

            if (val < 0.0)   val = 0.0;

            *qr++ = (uint8_T) val;

        }

    }

}

// single类型转换(处理方式和double类型一样)

void ConvertFromSingle(float *pr, uint8_T *qr, mwSize numElements) {

    mwSize k;

    float val;

    for (k = ; k < numElements; k++) {

        val = *pr++;

        if (mxIsNaN(val))

            *qr++ = ;

        else {

            val = val * 255.0f + 0.5f;

            if (val > 255.0) val = 255.0;

            if (val < 0.0)   val = 0.0;

            *qr++ = (uint8_T) val;

        }

    }

}

// uint16类型转换

void ConvertFromUint16(uint16_T *pr, uint8_T *qr, mwSize numElements) {

    mwSize k;

    /*

     除以257的原因来自于uint16数字映射到uint8

     例如数字x转换到uint8

        y = x*255/65535

        由于257 = 65535/255，则y=x/257

    */

    double factor = 1.0 / 257.0;

    for (k = ; k < numElements; k++)

        *qr++ = (uint8_T) ( (double) (*pr++) * factor + 0.5 );

}

void ValidateInputs(int nrhs, const mxArray *prhs[]) {

    if (nrhs < ) {

        mexErrMsgIdAndTxt("Images:grayto8:tooFewInputs",

                          "%s","Too few input arguments.");

    }

    if (nrhs > ) {

        mexErrMsgIdAndTxt("Images:grayto8:tooManyInputs",

                          "%s","Too many input arguments.");

    }

    if (!mxIsDouble(prhs[]) && !mxIsUint16(prhs[]) && !mxIsSingle(prhs[])) {

        mexErrMsgIdAndTxt("Images:grayto8:invalidType",

                          "%s","Input must be double, single, or uint16.");

    }

    if (mxIsComplex(prhs[])) {

        mexWarnMsgIdAndTxt("Images:grayto8:ignoringImaginaryPartOfInput",

                           "%s","Ignoring imaginary part of input.");

    }

}

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {

    uint8_T *qr;

    (void) nlhs;  /* unused parameter */

    ValidateInputs(nrhs, prhs);

    plhs[] = mxCreateNumericArray(mxGetNumberOfDimensions(prhs[]),

                                   mxGetDimensions(prhs[]),

                                   mxUINT8_CLASS, mxREAL);

    qr = (uint8_T *) mxGetData(plhs[]);

    if (mxIsDouble(prhs[]))

        ConvertFromDouble((double *) mxGetData(prhs[]), qr, mxGetNumberOfElements(prhs[]));

    else if (mxIsUint16(prhs[]))

        ConvertFromUint16((uint16_T *) mxGetData(prhs[]), qr, mxGetNumberOfElements(prhs[]));

    else

        ConvertFromSingle((float *) mxGetData(prhs[]), qr, mxGetNumberOfElements(prhs[]));

}