--- a/bmpwrite.m
+++ b/bmpwrite.m
@@ -1,15 +1,26 @@
 ## bmpwrite(X,map,file)
-##   Write the bitmap X into file (8-bit uncompressed format).
+##   Write the bitmap X into file (8-bit indexed uncompressed).
 ##   The values in X are indices into the given RGB colour map.
+## bmpwrite(X,file)
+##   Write the bitmap X into file (24-bit truecolor uncompressed).
+##   X is an m x n x 3 array of R,G,B values.
 
 ## This code is in the public domain.
 ## Author: Paul Kienzle <pkienzle@users.sf.net>
-## Based information from Jörn Daub's web page:
-## http://www.daubnet.com/formats/BMP.html
 
 function bmpwrite(x,map,file)
-    header = 14+40+4*rows(map);
-    filesize = header+prod(size(x));
+  if nargin==2
+     bmpwrite_truecolor(x,map);
+  else
+     bmpwrite_indexed(x,map,file);
+  endif
+endfunction
+
+function bmpwrite_truecolor(x,file)
+    h = rows(x); w = columns(x);
+    padw = ceil(3*w/4)*4-3*w;
+    header = 14+40;
+    filesize = header+h*(3*w+padw);
     arch = "ieee-le";
     file = fopen(file, "wb");
     fwrite(file,toascii("BM"),"uchar",0,arch); # file tag
@@ -18,8 +29,43 @@
     fwrite(file,header,"long",0,arch);      # offset of raster data in file
 
     fwrite(file,40,"long",0,arch);          # header size
-    fwrite(file,columns(x),"long",0,arch);  # image width
-    fwrite(file,rows(x),"long",0,arch);     # image height
+    fwrite(file,w,"long",0,arch);           # image width
+    fwrite(file,h,"long",0,arch);           # image height
+    fwrite(file,1,"short",0,arch);          # number of planes
+    fwrite(file,24,"short",0,arch);         # pixels per plane
+    fwrite(file,0,"long",0,arch);           # compression (none)
+    fwrite(file,0,"long",0,arch);           # compressed size of image
+    resolution = 72/2.54*100;               # 72 dpi / 2.54 cm/in * 100 cm/m
+    fwrite(file,resolution,"long",0,arch);  # horizontal resolution
+    fwrite(file,resolution,"long",0,arch);  # vertical resolution
+    fwrite(file,0,"long",0,arch);           # number of colours used
+    fwrite(file,0,"long",0,arch);           # number of "important" colors
+
+    ## raster image, lines written bottom to top.
+    R = x(end:-1:1,:,1)';
+    G = x(end:-1:1,:,2)';
+    B = x(end:-1:1,:,3)';
+    RGB=[B(:),G(:),R(:)]';  # Now [[B;G;R],[B;G;R],...,[B;G;R]]
+    RGB=reshape(RGB,3*w,h); # Now [[B;G;R;...;B;G;R],...,[B;G;R;...;B;G;R]]
+    fwrite(file,[RGB;zeros(padw,h)],"uchar",0,arch);
+    fclose(file);
+endfunction
+
+function bmpwrite_indexed(x,map,file)
+    [h,w] = size(x);
+    padw = ceil(w/4)*4-w;
+    header = 14+40+4*rows(map);
+    filesize = header+(r+padw)*c;
+    arch = "ieee-le";
+    file = fopen(file, "wb");
+    fwrite(file,toascii("BM"),"uchar",0,arch); # file tag
+    fwrite(file,filesize,"long",0,arch);    # length of file
+    fwrite(file,0,"long",0,arch);           # reserved
+    fwrite(file,header,"long",0,arch);      # offset of raster data in file
+
+    fwrite(file,40,"long",0,arch);          # header size
+    fwrite(file,w,"long",0,arch);           # image width
+    fwrite(file,h,"long",0,arch);           # image height
     fwrite(file,1,"short",0,arch);          # number of planes
     fwrite(file,8,"short",0,arch);          # pixels per plane
     fwrite(file,0,"long",0,arch);           # compression (none)
@@ -37,7 +83,6 @@
 
     ## raster image, each line on a 32-bit boundary, padded with zeros
     ## lines written bottom to top.
-    fwrite(file,postpad(flipud(x-1)',ceil(columns(x)/4)*4),"uchar",0,arch);
+    fwrite(file,[flipud(x-1)',zeros(c,padw)],"uchar",0,arch);
     fclose(file);
 endfunction
-