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Re: [AutoTrace] autotrace 0.23

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  • Bernhard Herzog
    ... AFAICT, this has something to do with the new support for color images. Earlier versions only support B&W images and constructed a list of paths that were
    Message 1 of 20 , Sep 22, 2000
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      "Stewart C. Russell" <stewart@...> writes:

      > 0.24 seems to
      > get the inside of closed areas wrong, even on PBM input. I don't think
      > this is an architecture thing -- it happens on both x86-linux and
      > Sparc-Solaris.

      AFAICT, this has something to do with the new support for color images.

      Earlier versions only support B&W images and constructed a list of paths
      that were to be filled as a whole. In PostScript terms each of the list
      items consists of one moveto followed only by lineto's and curveto's adn
      all list items together form a postscript path that is filled.

      Autotrace now supports color input and each of the splines has a color
      parameter. When I updated the EPS, SVG and SK export code, I assumed
      that each of the paths would be filled individually and it worked for
      the images I tested it with. So I could be considered responsible for the
      Bugs.

      The best solution would be for autotrace to mark the splines that should
      be filled together. As a workaround it might be possible to just treat
      consecutive splines with the same fill color as subpath of the same
      postscript path and only start a new postscript path if the color
      changes. For SVG and SK simillar solutions should work.

      I've included a patch for the EPS code below.

      Bernhard

      PS: Martin, is there a list of contributers somewhere? There seem to
      have been several contributers by now, especially for output filters.
      The names I found by looking at a few files were in no particular order
      and probably incomplete:

      Kevin O' Gorman
      Reini Urban
      Ian MacPhedran
      Wolfgang Glunz
      Masatake YAMATO
      Bernhard Herzog


      Here the patch:

      *** output-eps.c.~1~ Tue Sep 19 20:19:04 2000
      --- output-eps.c Fri Sep 22 16:10:06 2000
      ***************
      *** 122,127 ****
      --- 122,128 ----
      out_splines (FILE * ps_file, spline_list_array_type shape)
      {
      unsigned this_list;
      + color_type last_color;

      for (this_list = 0; this_list < SPLINE_LIST_ARRAY_LENGTH (shape);
      this_list++)
      ***************
      *** 132,150 ****
      spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
      spline_type first = SPLINE_LIST_ELT (list, 0);

      ! c = k = 255 - list.color.r;
      ! m = 255 - list.color.g;
      ! if (m < k)
      ! k = m;
      ! y = 255 - list.color.b;
      ! if (y < k)
      ! k = y;
      ! c -= k;
      ! m -= k;
      ! y -= k;
      ! /* symbol k is used for CorelDraw 3/4 compatibility */
      ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
      ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
      OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");

      for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
      --- 133,156 ----
      spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
      spline_type first = SPLINE_LIST_ELT (list, 0);

      ! if (this_list == 0 || !COLOR_EQUAL(list.color, last_color))
      ! {
      ! if (this_list > 0)
      ! OUT_LINE ("f");
      ! c = k = 255 - list.color.r;
      ! m = 255 - list.color.g;
      ! if (m < k)
      ! k = m;
      ! y = 255 - list.color.b;
      ! if (y < k)
      ! k = y;
      ! c -= k;
      ! m -= k;
      ! y -= k;
      ! /* symbol k is used for CorelDraw 3/4 compatibility */
      ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
      ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
      ! }
      OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");

      for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
      ***************
      *** 160,167 ****
      END_POINT (s).x, END_POINT (s).y,
      "c");
      }
      ! OUT_LINE ("f");
      }
      }


      --- 166,175 ----
      END_POINT (s).x, END_POINT (s).y,
      "c");
      }
      ! last_color = list.color;
      }
      + if (SPLINE_LIST_ARRAY_LENGTH (shape) > 0)
      + OUT_LINE ("f");
      }





      --
      Bernhard Herzog | Sketch, a drawing program for Unix
      herzog@... | http://sketch.sourceforge.net/
    • Martin Weber
      Who is missing on the contributors list?
      Message 2 of 20 , Sep 22, 2000
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        Who is missing on the contributors list?

        Bernhard Herzog schrieb:

        >
        > "Stewart C. Russell" <stewart@...> writes:
        >
        > > 0.24 seems to
        > > get the inside of closed areas wrong, even on PBM input. I don't think
        > > this is an architecture thing -- it happens on both x86-linux and
        > > Sparc-Solaris.
        >
        > AFAICT, this has something to do with the new support for color images.
        >
        > Earlier versions only support B&W images and constructed a list of paths
        > that were to be filled as a whole. In PostScript terms each of the list
        > items consists of one moveto followed only by lineto's and curveto's adn
        > all list items together form a postscript path that is filled.
        >
        > Autotrace now supports color input and each of the splines has a color
        > parameter. When I updated the EPS, SVG and SK export code, I assumed
        > that each of the paths would be filled individually and it worked for
        > the images I tested it with. So I could be considered responsible for the
        > Bugs.
        >
        > The best solution would be for autotrace to mark the splines that should
        > be filled together. As a workaround it might be possible to just treat
        > consecutive splines with the same fill color as subpath of the same
        > postscript path and only start a new postscript path if the color
        > changes. For SVG and SK simillar solutions should work.
        >
        > I've included a patch for the EPS code below.
        >
        > Bernhard
        >
        > PS: Martin, is there a list of contributers somewhere? There seem to
        > have been several contributers by now, especially for output filters.
        > The names I found by looking at a few files were in no particular order
        > and probably incomplete:
        >
        > Kevin O' Gorman
        > Reini Urban
        > Ian MacPhedran
        > Wolfgang Glunz
        > Masatake YAMATO
        > Bernhard Herzog
        >
        > Here the patch:
        >
        > *** output-eps.c.~1~ Tue Sep 19 20:19:04 2000
        > --- output-eps.c Fri Sep 22 16:10:06 2000
        > ***************
        > *** 122,127 ****
        > --- 122,128 ----
        > out_splines (FILE * ps_file, spline_list_array_type shape)
        > {
        > unsigned this_list;
        > + color_type last_color;
        >
        > for (this_list = 0; this_list < SPLINE_LIST_ARRAY_LENGTH (shape);
        > this_list++)
        > ***************
        > *** 132,150 ****
        > spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
        > spline_type first = SPLINE_LIST_ELT (list, 0);
        >
        > ! c = k = 255 - list.color.r;
        > ! m = 255 - list.color.g;
        > ! if (m < k)
        > ! k = m;
        > ! y = 255 - list.color.b;
        > ! if (y < k)
        > ! k = y;
        > ! c -= k;
        > ! m -= k;
        > ! y -= k;
        > ! /* symbol k is used for CorelDraw 3/4 compatibility */
        > ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
        > ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
        > OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");
        >
        > for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
        > --- 133,156 ----
        > spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
        > spline_type first = SPLINE_LIST_ELT (list, 0);
        >
        > ! if (this_list == 0 || !COLOR_EQUAL(list.color, last_color))
        > ! {
        > ! if (this_list > 0)
        > ! OUT_LINE ("f");
        > ! c = k = 255 - list.color.r;
        > ! m = 255 - list.color.g;
        > ! if (m < k)
        > ! k = m;
        > ! y = 255 - list.color.b;
        > ! if (y < k)
        > ! k = y;
        > ! c -= k;
        > ! m -= k;
        > ! y -= k;
        > ! /* symbol k is used for CorelDraw 3/4 compatibility */
        > ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
        > ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
        > ! }
        > OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");
        >
        > for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
        > ***************
        > *** 160,167 ****
        > END_POINT (s).x, END_POINT (s).y,
        > "c");
        > }
        > ! OUT_LINE ("f");
        > }
        > }
        >
        >
        > --- 166,175 ----
        > END_POINT (s).x, END_POINT (s).y,
        > "c");
        > }
        > ! last_color = list.color;
        > }
        > + if (SPLINE_LIST_ARRAY_LENGTH (shape) > 0)
        > + OUT_LINE ("f");
        > }
        >
        >
        >
        > --
        > Bernhard Herzog | Sketch, a drawing program for Unix
        > herzog@... | http://sketch.sourceforge.net/
      • Ted Harding
        ... Great! This now works (at least in black and white). Many thanks, also for the explanations. Ted. ... E-Mail: (Ted Harding)
        Message 3 of 20 , Sep 22, 2000
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          On 22-Sep-00 Bernhard Herzog wrote:
          > The best solution would be for autotrace to mark the splines that
          > should be filled together. As a workaround it might be possible to
          > just treat consecutive splines with the same fill color as subpath of
          > the same postscript path and only start a new postscript path if the
          > color changes. For SVG and SK simillar solutions should work.
          >
          > I've included a patch for the EPS code below.

          Great! This now works (at least in black and white).
          Many thanks, also for the explanations.
          Ted.

          --------------------------------------------------------------------
          E-Mail: (Ted Harding) <Ted.Harding@...>
          Fax-to-email: +44 (0)870 284 7749
          Date: 22-Sep-00 Time: 17:43:50
          ------------------------------ XFMail ------------------------------
        • Bernhard Herzog
          ... The patch I posted contains a bug. The same code is used for EPS and AI and my patch doesn t generate a correct AI file, although it s a correct EPS file
          Message 4 of 20 , Sep 22, 2000
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            (Ted Harding) <Ted.Harding@...> writes:

            >
            > On 22-Sep-00 Bernhard Herzog wrote:
            > > The best solution would be for autotrace to mark the splines that
            > > should be filled together. As a workaround it might be possible to
            > > just treat consecutive splines with the same fill color as subpath of
            > > the same postscript path and only start a new postscript path if the
            > > color changes. For SVG and SK simillar solutions should work.
            > >
            > > I've included a patch for the EPS code below.
            >
            > Great! This now works (at least in black and white).
            > Many thanks, also for the explanations.
            > Ted.

            The patch I posted contains a bug. The same code is used for EPS and AI
            and my patch doesn't generate a correct AI file, although it's a correct
            EPS file (AFAICT, anyway).

            Here's a bette one, again against the original code of Autotrace 0.24a:

            *** output-eps.c.~1~ Tue Sep 19 20:19:04 2000
            --- output-eps.c Fri Sep 22 19:57:41 2000
            ***************
            *** 122,127 ****
            --- 122,128 ----
            out_splines (FILE * ps_file, spline_list_array_type shape)
            {
            unsigned this_list;
            + color_type last_color;

            for (this_list = 0; this_list < SPLINE_LIST_ARRAY_LENGTH (shape);
            this_list++)
            ***************
            *** 132,150 ****
            spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
            spline_type first = SPLINE_LIST_ELT (list, 0);

            ! c = k = 255 - list.color.r;
            ! m = 255 - list.color.g;
            ! if (m < k)
            ! k = m;
            ! y = 255 - list.color.b;
            ! if (y < k)
            ! k = y;
            ! c -= k;
            ! m -= k;
            ! y -= k;
            ! /* symbol k is used for CorelDraw 3/4 compatibility */
            ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
            ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
            OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");

            for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
            --- 133,157 ----
            spline_list_type list = SPLINE_LIST_ARRAY_ELT (shape, this_list);
            spline_type first = SPLINE_LIST_ELT (list, 0);

            ! if (this_list == 0 || !COLOR_EQUAL(list.color, last_color))
            ! {
            ! if (this_list > 0)
            ! OUT_LINE ("*U");
            ! c = k = 255 - list.color.r;
            ! m = 255 - list.color.g;
            ! if (m < k)
            ! k = m;
            ! y = 255 - list.color.b;
            ! if (y < k)
            ! k = y;
            ! c -= k;
            ! m -= k;
            ! y -= k;
            ! /* symbol k is used for CorelDraw 3/4 compatibility */
            ! OUT4 ("%f %f %f %f k\n", (double) c/255.0,
            ! (double) m/255.0,(double) y/255.0, (double) k/255.0);
            ! OUT_LINE ("*u");
            ! }
            OUT_COMMAND2 (START_POINT (first).x, START_POINT (first).y, "m");

            for (this_spline = 0; this_spline < SPLINE_LIST_LENGTH (list);
            ***************
            *** 161,167 ****
            --- 168,177 ----
            "c");
            }
            OUT_LINE ("f");
            + last_color = list.color;
            }
            + if (SPLINE_LIST_ARRAY_LENGTH (shape) > 0)
            + OUT_LINE ("*U");
            }




            --
            Bernhard Herzog | Sketch, a drawing program for Unix
            herzog@... | http://sketch.sourceforge.net/
          • Masatake YAMATO
            ... I ve applied this patch to the main source trunk. Masatake
            Message 5 of 20 , Sep 25, 2000
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              Bernhard Herzog wrote:
              > The patch I posted contains a bug. The same code is used for EPS and AI
              > and my patch doesn't generate a correct AI file, although it's a correct
              > EPS file (AFAICT, anyway).

              I've applied this patch to the main source trunk.

              Masatake
            • wgibbons@bigfoot.com
              ... and AI ... correct ... 0.24a: Thanks very much for your patch. Unfortunately I have a problem with anti-aliased bitmaps. Your patch cures the holes
              Message 6 of 20 , Sep 26, 2000
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                --- In autotrace@egroups.com, Bernhard Herzog <herzog@o...> wrote:

                > The patch I posted contains a bug. The same code is used for EPS
                and AI
                > and my patch doesn't generate a correct AI file, although it's a
                correct
                > EPS file (AFAICT, anyway).
                >
                > Here's a bette one, again against the original code of Autotrace
                0.24a:

                Thanks very much for your patch. Unfortunately I have a problem with
                anti-aliased bitmaps.

                Your patch cures the 'holes' problem for non anti-aliased bitmaps I
                have, but if I try to give AutoTrace an anti-aliased bitmap (eg of
                the letters 'Aa') I still get the holes filled in. Although I can
                see they grey bits aound the edges of the letters so I can actually
                see where the holes should be.

                Regards
                William Gibbons
              • Ted Harding
                ... You might like to try a pre-filtering with ImageMagick which I have found useful. Open the file with display ; in the Files menu select Effects and then
                Message 7 of 20 , Sep 26, 2000
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                  On 26-Sep-00 wgibbons@... wrote:
                  > Thanks very much for your patch. Unfortunately I have a problem with
                  > anti-aliased bitmaps.
                  >
                  > Your patch cures the 'holes' problem for non anti-aliased bitmaps I
                  > have, but if I try to give AutoTrace an anti-aliased bitmap (eg of
                  > the letters 'Aa') I still get the holes filled in. Although I can
                  > see they grey bits aound the edges of the letters so I can actually
                  > see where the holes should be.

                  You might like to try a pre-filtering with ImageMagick which I have
                  found useful.

                  Open the file with "display"; in the Files menu select Effects and
                  then Threshold. The default value of Threshold is 128; select a smaller
                  value experimentally (I usually end up with about 60).

                  I have used this for "noisy" scanned B&W images (with faint mottled
                  colours in the background), and it works well when the result is
                  submitted to autotrace. I reckon antialiasing is also noise in this
                  context!

                  Ted.

                  --------------------------------------------------------------------
                  E-Mail: (Ted Harding) <Ted.Harding@...>
                  Fax-to-email: +44 (0)870 284 7749
                  Date: 26-Sep-00 Time: 19:15:26
                  ------------------------------ XFMail ------------------------------
                • Bernhard Herzog
                  ... Well, the patch is a bit of a kludge. The real problem, AFAICT, is that the list of splines that autotrace creates and passes to the export filters doen t
                  Message 8 of 20 , Sep 26, 2000
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                    wgibbons@... writes:

                    > Your patch cures the 'holes' problem for non anti-aliased bitmaps I
                    > have, but if I try to give AutoTrace an anti-aliased bitmap (eg of
                    > the letters 'Aa') I still get the holes filled in. Although I can
                    > see they grey bits aound the edges of the letters so I can actually
                    > see where the holes should be.

                    Well, the patch is a bit of a kludge. The real problem, AFAICT, is that
                    the list of splines that autotrace creates and passes to the export
                    filters doen't contain enough information to make a correct postscript
                    output in all cases. Could you send me (by private mail) a sample image
                    that shows the problem? I'd like to find out what's going on.

                    --
                    Bernhard Herzog | Sketch, a drawing program for Unix
                    herzog@... | http://sketch.sourceforge.net/
                  • William Gibbons
                    Hi, You asked for a file which exhibits this problem, so I m sending you a .BMP file. I don t think there s anything particularly special about this file,
                    Message 9 of 20 , Sep 26, 2000
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                      Hi,

                      You asked for a file which exhibits this problem, so I'm sending you a .BMP
                      file. I don't think there's anything particularly special about this file,
                      I've had the same problem with other similar files.

                      Thanks for your speedy response.

                      Regards
                      William

                      ----- Original Message -----
                      From: Bernhard Herzog <herzog@...>
                      To: <autotrace@egroups.com>
                      Sent: Tuesday, September 26, 2000 10:00 PM
                      Subject: Re: [AutoTrace] Re: autotrace 0.23


                      > wgibbons@... writes:
                      >
                      > > Your patch cures the 'holes' problem for non anti-aliased bitmaps I
                      > > have, but if I try to give AutoTrace an anti-aliased bitmap (eg of
                      > > the letters 'Aa') I still get the holes filled in. Although I can
                      > > see they grey bits aound the edges of the letters so I can actually
                      > > see where the holes should be.
                      >
                      > Well, the patch is a bit of a kludge. The real problem, AFAICT, is that
                      > the list of splines that autotrace creates and passes to the export
                      > filters doen't contain enough information to make a correct postscript
                      > output in all cases. Could you send me (by private mail) a sample image
                      > that shows the problem? I'd like to find out what's going on.
                      >
                      > --
                      > Bernhard Herzog | Sketch, a drawing program for Unix
                      > herzog@... | http://sketch.sourceforge.net/
                      >
                      >
                      >
                      >
                    • wgibbons@bigfoot.com
                      ... Thanks for the suggestion. I don t believe the anti-aliasing is directly responsible for the problem - it s a pretty large hole - but indirectly, perhaps.
                      Message 10 of 20 , Sep 26, 2000
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                        --- In autotrace@egroups.com, (Ted Harding) <Ted.Harding@N...> wrote:
                        > I have used this for "noisy" scanned B&W images (with faint mottled
                        > colours in the background), and it works well when the result is
                        > submitted to autotrace. I reckon antialiasing is also noise in this
                        > context!

                        Thanks for the suggestion. I don't believe the anti-aliasing is
                        directly responsible for the problem - it's a pretty large hole - but
                        indirectly, perhaps.

                        As for anti-aliasing being noise, well...anti-aliasing is a way of
                        simulating a higher resolution display than you actually have. If
                        it's done properly, you can send more information about the paths
                        than you can with the same resolution monochrome bitmap, because (for
                        instance) a mid-grey pixel indicates that a pixel should be half-
                        covered by a path, and you can't indicate this with monochrome (or
                        non-anti-aliased bitmaps).

                        However, it may well be that trying to extract this information and
                        use it to improve curve tracing would be more trouble than it's
                        worth. I don't think it's a trivial problem. So yes, perhaps the
                        best solution is to remove anti-aliasing with a noise filter.
                        However, I'm not sure this helps if you're trying to trace
                        photographs.
                      • wgibbons@bigfoot.com
                        ... [ 23K binary included ] Sorry about this, I didn t mean to send this mail to the discussion... William
                        Message 11 of 20 , Sep 26, 2000
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                          --- In autotrace@egroups.com, "William Gibbons" <wgibbons@b...> wrote:

                          [ 23K binary included ]

                          Sorry about this, I didn't mean to send this mail to the discussion...

                          William
                        • Ted Harding
                          ... Attached are two EPS files: text.eps is the autotrace conversion (using 0.24a with patched output-eps.c) of William Gibbons s original file text.bmp
                          Message 12 of 20 , Sep 27, 2000
                          • 0 Attachment
                            On 26-Sep-00 William Gibbons wrote:
                            > Hi,
                            >
                            > You asked for a file which exhibits this problem, so I'm sending you a
                            > .BMP file. I don't think there's anything particularly special about
                            > this file, I've had the same problem with other similar files.

                            Attached are two EPS files:

                            text.eps is the autotrace conversion (using 0.24a with patched
                            output-eps.c) of William Gibbons's original file text.bmp

                            text2.eps is the result of running autotrace on a BMP file obtained
                            by running the noise-filtering I described previously (using the
                            "display" program from ImageMagick and lowering the threshold
                            -- in this case to a hit-or-miss value of 64).

                            The hit-or-miss seems to have hit it spot on.

                            Note also the difference in file size ... !

                            Ted.

                            --------------------------------------------------------------------
                            E-Mail: (Ted Harding) <Ted.Harding@...>
                            Fax-to-email: +44 (0)870 284 7749
                            Date: 27-Sep-00 Time: 15:08:28
                            ------------------------------ XFMail ------------------------------
                          • Stefan A. Deutscher
                            ... Hi Ted, hi all, can we keep (binary) attachments down to a minimum, please? Sometimes direct exchange between the involved folks might be enough. The
                            Message 13 of 20 , Sep 27, 2000
                            • 0 Attachment
                              On Wed, Sep 27, 2000 at 03:08:29PM +0100, Ted Harding wrote:
                              > On 26-Sep-00 William Gibbons wrote:
                              > > You asked for a file which exhibits this problem, so I'm sending you
                              > > a .BMP file. I don't think there's anything particularly special
                              > > about this file, I've had the same problem with other similar files.
                              >
                              > Attached are two EPS files: text.eps is the autotrace conversion
                              > (using 0.24a with patched output-eps.c) of William Gibbons's original
                              > file text.bmp text2.eps is the result of running autotrace on a BMP
                              > file obtained by running the noise-filtering I described previously
                              > (using the "display" program from ImageMagick and lowering the
                              > threshold -- in this case to a hit-or-miss value of 64). The
                              > hit-or-miss seems to have hit it spot on. Note also the difference in
                              > file size ... ! Ted.

                              Hi Ted, hi all,

                              can we keep (binary) attachments down to a minimum, please? Sometimes
                              direct exchange between the involved folks might be enough. The problem
                              is that I, for one, am accessing my email over a 14.4k dial-up modem and
                              in this part of the world even local calls are metered to be paid.

                              Thanks & Cheers,

                              Stefan


                              --
                              ============================================================================
                              Stefan A. Deutscher |
                              Donostia International Physics Center | office: ++34-943-018174
                              Universidad del Pais Vasco, Facultad de Quimica | fax : ++34-943-015600
                              Departamento de Fisica de Materiales | home : ++34-943-270647
                              Apartado 1072, San Sebastian 20080, Spain | email : sad@...
                              ============================================================================
                              The early bird gets the worm but the second mouse gets the cheese.
                            • William Gibbons
                              ... Yes. One would expect this given the way that AutoTrace seems to handle the tracing of anti-aliased bitmaps. If I had simply wanted to get a more
                              Message 14 of 20 , Sep 27, 2000
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                                Ted Harding wrote:

                                > Note also the difference in file size ...

                                Yes. One would expect this given the way that AutoTrace seems to handle the
                                tracing of anti-aliased bitmaps. If I had simply wanted to get a more
                                accurate trace of the characters, I would have chosen to export with
                                anti-aliasing turned off. I was really just trying to report what I believe
                                to be a bug - the fact that the holes are filled in shouldn't happen,
                                regardless of the anti-aliasing.

                                Some other bitmap trace algorithms perform differently with anti-aliased
                                bitmaps, even with noise filters turned off. As I said, I believe there are
                                better ways to deal with anti-aliased bitmaps than simply treating
                                anti-aliasing as noise, and indeed dithering is a fact of life for tracing
                                photographs etc.

                                William
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