Identify from ImageMagick prints output using wrong units.

Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
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Petr
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Identify from ImageMagick prints output using wrong units.

Post by Petr » 2010-04-23T00:55:51-07:00

Original report at

https://bugzilla.novell.com/show_bug.cgi?id=598714

I tested it with several images, always the same problem.

comp> identify -units PixelsPerInch -verbose -format "%x %y %z" test2.png
236.22 PixelsPerInch 236.22 PixelsPerInch 8
comp> identify -verbose -format "%x %y %z" test2.png
236.22 PixelsPerCentimeter 236.22 PixelsPerCentimeter 8

Correct is:

laura:/> identify -verbose -units PixelsPerInch -format "%x %y %z" test2.png
599.999 PixelsPerInch 599.999 PixelsPerInch 8
laura:/> identify -verbose -format "%x %y %z" test2.png
236.22 PixelsPerCentimeter 236.22 PixelsPerCentimeter 8

Petr
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Re: Identify from ImageMagick prints output using wrong unit

Post by Petr » 2010-04-23T01:03:12-07:00

Please consider following patch. Maybe is stupid, I don't know the ImageMagick much to know all the context.

Code: Select all

Index: ImageMagick-6.6.1-0/magick/image.c
===================================================================
--- ImageMagick-6.6.1-0.orig/magick/image.c
+++ ImageMagick-6.6.1-0/magick/image.c
@@ -3959,6 +3959,9 @@ MagickExport MagickBooleanType SyncImage
   MagickStatusType
     flags;

+  ResolutionType
+    units;
+
   /*
     Sync image options.
   */
@@ -4150,16 +4153,18 @@ MagickExport MagickBooleanType SyncImage
       option);
   option=GetImageOption(image_info,"units");
   if (option != (const char *) NULL)
-    image->units=(ResolutionType) ParseMagickOption(MagickResolutionOptions,
+    units=(ResolutionType) ParseMagickOption(MagickResolutionOptions,
       MagickFalse,option);
-  if (image_info->units != UndefinedResolution)
+  else
+    units = image_info->units;
+  if (units != UndefinedResolution)
     {
-      if (image->units != image_info->units)
+      if (image->units != units)
         switch (image->units)
         {
           case PixelsPerInchResolution:
           {
-            if (image_info->units == PixelsPerCentimeterResolution)
+            if (units == PixelsPerCentimeterResolution)
               {
                 image->x_resolution/=2.54;
                 image->y_resolution/=2.54;
@@ -4168,7 +4173,7 @@ MagickExport MagickBooleanType SyncImage
           }
           case PixelsPerCentimeterResolution:
           {
-            if (image_info->units == PixelsPerInchResolution)
+            if (units == PixelsPerInchResolution)
               {
                 image->x_resolution*=2.54;
                 image->y_resolution*=2.54;
@@ -4178,7 +4183,7 @@ MagickExport MagickBooleanType SyncImage
           default:
             break;
         }
-      image->units=image_info->units;
+      image->units=units;
     }
   option=GetImageOption(image_info,"white-point");
   if (option != (const char *) NULL)

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magick
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Re: Identify from ImageMagick prints output using wrong unit

Post by magick » 2010-04-23T07:15:56-07:00

We can reproduce the problem you posted and have included your patch in ImageMagick 6.6.1-5 Beta available by sometime tomorrow. Thanks.

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fmw42
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Re: Identify from ImageMagick prints output using wrong unit

Post by fmw42 » 2010-04-23T08:23:05-07:00

Perhaps I misunderstand the issue. But...

PNG only supports pixelspercentimeter. IM converts density from pixelsperinch if supplied that way to the correct density at pixelspercentimeter when creating a PNG.

Drarakel
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Re: Identify from ImageMagick prints output using wrong unit

Post by Drarakel » 2010-04-24T00:26:32-07:00

fmw42 wrote:PNG only supports pixelspercentimeter. IM converts density from pixelsperinch if supplied that way to the correct density at pixelspercentimeter when creating a PNG.
Yes, but there should be a way to recreate the 'PixelsPerInch value' IMO. When I have a 300dpi image, most programs do report the file as 300 dpi - even when it's stored with PixelsPerCentimeter internally. (Well, the Windows image info has some sort of rounding error there, because i see sometimes 299dpi when another software reports 300dpi.) And if I convert that file (with e.g. 118.11 PixelsPerCentimeter) to JPG, it gets written as 300 PixelsPerInch automatically with these programs. Which is what I want. (Even though I'm from Europe, and in other areas I'm used to centimeter - not to inches. :))
With the last ImageMagick versions, I couldn't accomplish that task. (Or did I miss something there?) I had to enter the density value manually again, as a "convert input.png -units PixelsPerInch output.jpg" command only changed the unit, but did not convert back the density value. (Which is basically the same issue that Petr reported.) And: It also did introduce another kind of 'rounding error' - as a simple "convert input.png output.jpg" command did change a 300dpi file (118.11 PPI) to a file that most programs did report as 299dpi (as the value is 118.0 PPI then in the JPG - of course I don't call that a bug).

Edit: Indeed, changing the unit/density works now with IM v6.6.1-5 (identify and convert). Thanks!

By the way (I think this is a bit related to this PixelsPerInch/PixelsPerCentimeter issue): It would be even better if the "Print size" could be output in inches AND centimeters (or be specified with an additional parameter). For example, if I have a 300dpi image that is approx. DIN A3 in size, I usually want to know the print size in centimeters (29,7x42cm), but the density in PixelsPerInch. Up till now I have to use two separate commands to get that.

Drarakel
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Re: Identify from ImageMagick prints output using wrong unit

Post by Drarakel » 2010-04-24T15:12:25-07:00

There is still some rounding issue IMO.
Example: Again, I have a 300dpi PNG. "identify -verbose" shows the correct info for that:

Code: Select all

  Resolution: 118.11x118.11
  Print size: 21.607x30.3361
  Units: PixelsPerCentimeter
"identify -verbose -units PixelsPerInch" correctly shows the converted values now:

Code: Select all

  Resolution: 299.999x299.999
  Print size: 8.50668x11.9434
  Units: PixelsPerInch
But if I convert that to a JPG with "convert input.png -units PixelsPerInch output.jpg", I get that:

Code: Select all

  Resolution: 299x299
  Print size: 8.53512x11.9833
  Units: PixelsPerInch
I think, the density should be mathematically rounded here (to 300x300), if the.. decimal places can't be kept. Is that possible?

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magick
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Re: Identify from ImageMagick prints output using wrong unit

Post by magick » 2010-04-24T16:39:10-07:00

We can reproduce the problem you posted and have included your patch in ImageMagick 6.6.1-6 Beta available by sometime tomorrow. Thanks.

Drarakel
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Re: Identify from ImageMagick prints output using wrong unit

Post by Drarakel » 2010-04-24T20:08:41-07:00

Great! Thanks! :)

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Re: Identify from ImageMagick prints output using wrong unit

Post by Drarakel » 2010-05-08T12:17:46-07:00

The rounding of the density values is better now (IM v6.6.1-6), thanks! But it doesn't work for all cases..

An example with a 96dpi PNG.. "identify -verbose" shows for that file:

Code: Select all

  Resolution: 37.8x37.8
  Print size: 21.5873x30.291
  Units: PixelsPerCentimeter
"identify -verbose -units PixelsPerInch" shows a correct value in inches:

Code: Select all

  Resolution: 96.01x96.01
  Print size: 8.49911x11.9258
  Units: PixelsPerInch
If I make a JPG with "convert input.png -units PixelsPerInch output.jpg", I get again fine values:

Code: Select all

  Resolution: 96x96
  Print size: 8.5x11.9271
  Units: PixelsPerInch
But with "convert input.png output.jpg", the resulting JPG shows this:

Code: Select all

  Resolution: 37x37
  Print size: 22.0541x30.9459
  Units: PixelsPerCentimeter
With "identify -verbose -units PixelsPerInch" on that file:

Code: Select all

  Resolution: 93.98x93.98
  Print size: 8.6827x12.1834
  Units: PixelsPerInch
So, a simple convert from PNG to JPG can 'change' the density from e.g. 96dpi to 93dpi.
Of course, there will always be a small loss of information with the conversions. But I think it would be better if the density was always rounded up mathematically when the result is written to a format with less precision. In the above example, the 37.8 ppc should be rounded to 38 ppc (and not 'cut off' to 37 ppc). I don't know though if that's easily possible.

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magick
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Re: Identify from ImageMagick prints output using wrong unit

Post by magick » 2010-05-08T12:51:57-07:00

We can reproduce the problem you posted and have included your patch in ImageMagick 6.6.1-8 Beta available by sometime tomorrow. Thanks.

Drarakel
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Re: Identify from ImageMagick prints output using wrong unit

Post by Drarakel » 2010-05-08T13:44:01-07:00

magick wrote:6.6.1-8 Beta
That goes fast! :shock: Thanks! :)

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