Re: imread.m

[John W. Eaton]

On 15-Jul-2008, Daniel J Sebald wrote:

| Daniel J Sebald wrote:
| > On 15-Jul-2008, Thomas L. Scofield wrote:
| > 
| > | Just got your message about it being imshow.  Can it be the source of  
| > | the problem I describe here, too?
| > 
| > Yes, I think the problem is that uint8 images of size MxNx3 are not
| > displayed properly by imshow.  For example, try this:
| > 
| >  imshow (uint8 (repmat (kron ((0:255)', ones (1, 200)), [1, 1, 3])))
| > 
| > It should show a smooth black to white gradient from top to bottom,
| > but I see the attached image instead.
| 
| I haven't updated to Mercurial and the latest code yet so can't put together 
a patch.  But I think I see what the problem is.  Perhaps a lower level routine 
no longer automatically ranges the data.  This test in imshow.m is true for 
your example:
| 
|   elseif (size (im, 3) == 3)
|     if (ismember (class (im), {"uint8", "uint16", "double", "single"}))
|       true_color = true;
| 
| This means it is to be an rgb image in "truecolor".  In that case, scaling of 
data is NOT done:
| 
|   ## Scale the image to the interval [0, 1] according to display_range.
|   if (! (true_color || indexed || islogical (im)))
| 
| So, the questions are.  What does "truecolor" mean here?  Does it simply mean 
RGB?  Or does it mean RGB and no data scaling?  The help for imshow simply says 
that RGB.  If the data came from a file, I could see that no scaling should be 
applied.  (But that is already present as "indexed".)  But if the data comes 
from the command line, like John's example, I'd say no.
| 
| My thinking is that "true_color" should be removed from the scaling test 
above.  I don't think TrueColor images have any implicit scaling properties, 
just that a colormap is not used.

The following patch seems to fix the problem for me, and also improves
compatibility with regard to the way cdata is stored and clim is
computed.  But maybe I messed up something else with this change, so
it would help if people who work with images could do some testing.

Thanks,

jwe

# HG changeset patch
# User John W. Eaton <address@hidden>
# Date 1216221888 14400
# Node ID 1f6eb3de1c4ef4726e14cb4a7f945f059b5fd087
# Parent  30b952e90c294c6601e8f812e8a746024f91fd5a
__img__.m, imshow.m, __go_draw_axes__.m: improve handling of truecolor images

diff --git a/scripts/ChangeLog b/scripts/ChangeLog
--- a/scripts/ChangeLog
+++ b/scripts/ChangeLog
@@ -1,3 +1,11 @@
+2008-07-16  John W. Eaton  <address@hidden>
+
+       * image/__img__.m: Set clim for true-color integer data.
+
+       * image/imshow.m: Don't convert integer true-color data to double.
+
+       * plot/__go_draw_axes__.m: Recognize 3-d cdata as a true-color image.
+
 2008-07-14  John W. Eaton  <address@hidden>
 
        * image/Makefile.in (SOURCES): Add imread.m to the list.
diff --git a/scripts/image/__img__.m b/scripts/image/__img__.m
--- a/scripts/image/__img__.m
+++ b/scripts/image/__img__.m
@@ -56,6 +56,15 @@
   tmp = __go_image__ (ca, "cdata", img, "xdata", xlim, "ydata", ylim, 
                      "cdatamapping", "direct", varargin {:});
 
+  if (ndims (img) == 3)
+    if (isinteger (img))
+      c = class (img);
+      mn = intmin (c);
+      mx = intmax (c);
+      set (ca, "clim", double ([mn, mx]));
+    endif
+  endif
+
   set (ca, "view", [0, 90]);
 
   if (strcmp (get (ca, "nextplot"), "replace"))
diff --git a/scripts/image/imshow.m b/scripts/image/imshow.m
--- a/scripts/image/imshow.m
+++ b/scripts/image/imshow.m
@@ -147,7 +147,7 @@
   endif
 
   ## This is for compatibility.
-  if (! indexed || islogical (im))
+  if (! (indexed || (true_color && isinteger (im))) || islogical (im))
     im = double (im);
   endif
 
diff --git a/scripts/plot/__go_draw_axes__.m b/scripts/plot/__go_draw_axes__.m
--- a/scripts/plot/__go_draw_axes__.m
+++ b/scripts/plot/__go_draw_axes__.m
@@ -291,6 +291,7 @@
     zautoscale = strcmpi (axis_obj.zlimmode, "auto");
     cautoscale = strcmpi (axis_obj.climmode, "auto");
     cdatadirect = false;
+    truecolor = false;
 
     kids = axis_obj.children;
 
@@ -338,7 +339,9 @@
 
          if (use_gnuplot_for_images)
 
-           if (strcmpi (obj.cdatamapping, "direct"))
+           if (ndims (img_data) == 3)
+             truecolor = true;
+           elseif (strcmpi (obj.cdatamapping, "direct"))
              cdatadirect = true;
            endif
            fputs (plot_stream, "set border front;\n");
@@ -1056,11 +1059,12 @@
 
     cmap = parent_figure_obj.colormap;    
     cmap_sz = rows(cmap);
+
     if (! any (isinf (clim)))
-      if (cdatadirect)
+      if (truecolor || ! cdatadirect)
+       fprintf (plot_stream, "set cbrange [%g:%g];\n", clim);
+      else
        fprintf (plot_stream, "set cbrange [1:%d];\n", cmap_sz);
-      else
-       fprintf (plot_stream, "set cbrange [%g:%g];\n", clim);
       endif
     endif