c# - Extracted thumbnail from DNG image using DCRaw -

i using dcraw command line utility extract thumbnails dng images. thumbnail colors way off , inverting them not help.

i took photo camera , preview looks this:

here how call dcraw:

 settings osettings = settings.getinstance();  var startinfo = new processstartinfo(dcrawpath)  {     arguments = "-e \"" + sinputfilename + "\"",     useshellexecute = true,     redirectstandardoutput = false,     windowstyle = processwindowstyle.hidden,     createnowindow = true,     workingdirectory = rootdirectory  };  var process = process.start(startinfo); 

the result ppm file looks this:

i tried inverting thumbnail using code:

static readonly colormatrix _inversecolormatrix = new colormatrix(new[] {    new float[] {-1, 0, 0, 0, 0},    new float[] {0, -1, 0, 0, 0},    new float[] {0, 0, -1, 0, 0},    new float[] {0, 0, 0, 1, 0},    new float[] {1, 1, 1, 0, 1} });  public static bitmap inverseimage(bitmap source) {    var newbitmap = new bitmap(source.width, source.height);    using (var g = graphics.fromimage(newbitmap))    {       var attributes = new imageattributes();       attributes.setcolormatrix(_inversecolormatrix);       g.drawimage(source, new rectangle(0, 0, source.width, source.height),                             0, 0, source.width, source.height, graphicsunit.pixel, attributes);    }     return newbitmap; } 

this gave me thumbnail so:

i got same result using photoshop means code inverting image correctly seems not way parse dng thumbnails.

how can invert thumbnail generated dcraw give correct colors first image.

note: camera lumia 1020 dng output.

edit: original dng file can downloaded here