Windows – Error “Invalid Parameter” fom ImageMagick convert on Windows

asp.netimagemagickwindows

I am trying to convert a PDF document into a PNG file using ImageMagick command line tools from a ASP.NET website. I create a new shell process and ahve it execute the following command:

convert -density 96x96 "[FileNameAndPath].pdf" "[FileNameAndPath].png"

This runs well when testing the website on my local machine with the ASP.NET Develeopment Server of VS and the command also works well when manually entered into the shell. When running from the programatically created shell in ASP.NET there is the following error message:

Invalid Parameter - 96x96

Does anybody know why that happens and what to do?

I have tested the command while being logged in on the server via RDP with a different user account than the ASP.NET process. I have used exactly the same ImageMagick and Ghostscript installation files as on my local machine and have activated adding the ImageMagick installation path to the enironment variables during installing. The server has not been rebooted since than.

Best Answer

convert is also the name of a windows executable which converts FAT filesystem to NTFS. When you do not specify the full path of an executable, quote:

...the system first searches the current working directory and then searches the path environment variable, examining each directory from left to right, looking for an executable filename that matches the command name given.

"C:\Windows\System32" is generally present in the beginning of %PATH% variable, causing the Windows convert utility to launch, which fails with "Invalid Parameter" error as expected.

Try specifying the full path of the ImageMagick's convert.exe like so:

"C:\Program Files\ImageMagick\convert.exe" -density 96x96 "path_and_filename.pdf" "path_and_filename.png"

Related Solutions

Converting a PDF to PNG

You can use one commandline with two commands (gs, convert) connected through a pipe, if the first command can write its output to stdout, and if the second one can read its input from stdin.

Luckily, gs can write to stdout (... -o %stdout ...).
Luckily, convert can read from stdin (convert -background transparent - output.png).

Problem solved:

GS used for alpha channel handling a special image,
convert used for creating transparent background,
pipe used to avoid writing out a temp file on disk.

Complete solution:

gs -sDEVICE=pngalpha       \
   -o %stdout              \
   -r144 cover.pdf         \
   |                       \
convert                    \
   -background transparent \
   -                       \
    cover.png

Update

If you want to have a separate PNG per PDF page, you can use the %d syntax:

gs -sDEVICE=pngalpha -o file-%03d.png -r144 cover.pdf

This will create PNG files named page-000.png, page-001.png, ... (Note that the %d-counting is zero-based -- file-000.png corresponds to page 1 of the PDF, 001 to page 2...

Or, if you want to keep your transparent background, for a 100-page PDF, do

for i in {1..100}; do        \
                             \
  gs -sDEVICE=pngalpha       \
     -dFirstPage="${i}"      \
     -dLastPage="${i}"       \
     -o %stdout              \
     -r144 input.pdf         \
     |                       \
  convert                    \
     -background transparent \
     -                       \
      page-${i}.png ;        \
                             \
done

Convert PDF to PNG using ImageMagick

Reducing the image size before output results in something that looks sharper, in my case:

convert -density 300 a.pdf -resize 25% a.png

Best Answer

Related Solutions

Converting a PDF to PNG

Update

Convert PDF to PNG using ImageMagick

Related Topic