Imagemagick convert returns “no decode delegate for this image format”

command lineimagemagick

I am trying to use this command for ImageMagick:

convert "c:\users\****\My Documents\test.png"  -transparent white   test2.png

However, I keep on getting two errors that look like this:

convert.exe: unable to open image `c:\users\****\My':  
 No such file or directory @ error/blob.c/OpenBlob/2641.

convert.exe: no decode delegate for this image format `c:\users\****\My' 
 @ error/constitute.c/ReadImage/550.

I installed ImageMagick to my c:\ directory.

What does this mean, and how can I fix it?

Best Answer

Sure looks like the space between My and Documents is being used as an argument separator by the convert program.

Not being a windows guru, I'm not sure how you'd escape the space.

Being practical, I'd say to move test.png to a directory string that contains no special characters and then running convert on it.

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Hence, to convert from ppt to jpg you could use something like this:

unoconv <filename>.ppt <filename>.pdf
convert <filename>.pdf <filename>.jpg

where is the name of the file you want to convert without the extension.

Linux – Convert grayscale image into alpha channel image in unix shell

Ooookay. After plenty of googling, and reading for more of the ImageMagick manual than I actually care for, here's the answer. Given that you have a grayscale image called source.png, here are my commands.

To make the make the black pixels transparent and keeps the white pixels as they are, run this command:

 convert source.png -alpha copy -fx '#fff' result.png

To instead make the white pixels transparent while keeping the black as-is, use:

 convert source.png -alpha copy -channel alpha -negate +channel -fx '#000' result.png

Let's explain that last command a bit more thoroughly:

convert – Is the ImageMagic command (one of several)
source.png – The greyscale source image.
-alpha copy – Copy contents of the previous file into the alpha channel.
-channel alpha – Specify that following operators only should affect the alpha channel.
-negate – Invert the alpha channel (will, because of the previous -chanel alpha not affect any other part of the image).
+channel – Specify that following operators only should should affect the color channels, and no longer modify the alpha channel. (This is the default, and therefore we need not provide it in the first, simpler example.)
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It is quite important to include that final -fx option, otherwise all semi-transparent pixels in generated image will retain colors. (Since these pixels are half-transparent, it might not be obvious, but the end result is not what one expect.)

I found the list of ImageMagick options quite useful.

Best Answer

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