Page 1 of 1

Pdf convertion issue

Posted: 2009-01-25T12:04:36-07:00
by broucaries
from http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=445574

> with the debian logo from
> http://www.debian.org/logos/openlogo-nd-50.png
> and can easily reproduce the problem, by comparing the output of
> the following two commands:
>
> convert openlogo-nd-50.png test.pdf
> convert openlogo-nd-50.png -density 72 test.pdf
>
> According to the documentation, the default density value is 72 dpi,
> and the default unit for the density option is dpi, so the output
> pdf files should look the same.
> However, they don't: the second command results in a pdf file with
> a much smaller picture.
>
> Strangely, when trying with another debian picture, namely from
> http://www.debian.org/Pics/debian.png
> the bug doesn't occur: both pdf's look identical.

I can confirm this bug with a more recent version

>As far as I can see, the default conversion is done at 72 dpi, as it
>should; but the _other_ testcase (i.e., with the -density 72 option)
>does _not_ use 72 dpi (but perhaps 72 dots per cm).

Thank you

Bastien

Re: Pdf convertion issue

Posted: 2009-01-25T12:45:41-07:00
by magick
This particular image has units of pixels per centimeter:
  • -> identify -verbose openlogo-nd-50.png
    Image: openlogo-nd-50.png
    Format: PNG (Portable Network Graphics)
    Class: PseudoClass
    Geometry: 50x61+0+0
    Resolution: 28.34x28.34
    Print size: 1.76429x2.15243
    Units: PixelsPerCentimeter
    Type: Palette
    Endianess: Undefined
    Colorspace: RGB
    Depth: 8-bit
To get the results the user is looking for, use this command:
  • convert openlogo-nd-50.png -units pixels-per-inch -density 72 2.pdf

Re: Pdf convertion issue

Posted: 2009-01-25T12:50:16-07:00
by broucaries
Ok will forward to the user. But according to the documentation:

http://www.imagemagick.org/script/comma ... hp#density

>this option specifies the image resolution to store while encoding a raster image or the canvas resolution while rendering (reading) vector formats such as >Postscript, PDF, WMF, and SVG into a raster image. Image resolution provides the unit of measure to apply when rendering to an output device or raster image. >The default unit of measure is in dots per inch (DPI). The -units option may be used to select dots per centimeter instead.

>The default resolution is 72 dots per inch, which is equivalent to one point per pixel (Macintosh and Postscript standard). Computer screens are normally 72 or 96 >dots per inch while printers typically support 150, 300, 600, or 1200 dots per inch. To determine the resolution of your display, use a ruler to measure the width of >your screen in inches, and divide by the number of horizontal pixels (1024 on a 1024x768 display).

Therefore convert does not behave as expected, the two image should be the same :( 72 should means 72 dpi and by default you should use 72 dpi
May be a documentation problem?

Regards

Re: Pdf convertion issue

Posted: 2009-01-25T13:33:47-07:00
by magick
The default resolution is 72DPI. That's a density of 72 and units of pixels-per-inch. Both are needed to specify the resolution. The density option is just a number. Its meaning requires the units option as well. We will work towards improving the documentation for density.

Re: Pdf convertion issue

Posted: 2011-10-12T05:24:38-07:00
by broucaries
Any news of this documentation bug?