Legacy ImageMagick Discussions Archive

Hi!

Due to the fact that I slowly but surely go crazy trying out what I have to set in which way I decided to simply ask, even if it will be a really easy solution.

First of all my environment:
ImageMagick: 6.6.9-4 2011-04-01 Q16
GhostScript: 9.02
OS: Windows 7 Pro x64

What I want to do:
I have some pdf-files that I should convert to jpg-images, but two things I have to keep in mind converting them:

1. they have to have 300dpi
2. they have a maximum size of w: 990px an h: 1400px.

As far as I have seen the pdfs have transparent background, but I don't even know if that has to do with my problem. If I convert it with
all is good, except the imagesize. If I change it to:
I have the right dpis, the right size BUT the formerly transparent background went black. So... any ideas what I can do? And yes, if I scale down the images from my first convert-call, the image is OK. But somehow it has to go in one statement, right?

It went black because JPEG images do not save transparency!!!

It did not appear before because typically -- transparency has color -- In this case white from the PDF conversion! Resizing the image removed that color, setting it to black, because mathematically the color of a transparent area does not matter!

See... JPEG transparency - NOT
http://www.imagemagick.org/Usage/formats/#jpg_trans

For solutions see Removing Transparency
http://www.imagemagick.org/Usage/masking/#remove

You can remove the transparency either before or after the resize, that does not matter.

First of all... sorry for the late reply, but I was on holiday and had no time to check back here.

Thanks a lot for the answer but I want also to clearify something... I know that jpeg don't use transparency, that means that I simply wonder why ImageMagick renders it once with a white background and a different time with black background, thats all. I know that you stated why, but if you don't know what happens in the background (during the conversion) its simply not understandable

I will add my solution as soon as I have it. *goes over testing*

Edit:
And here we go:

The -background white does nothing in the above. -alpha off will just turn off transparency making the existing (white) color valid.

If you want to force transparency to white, replace -alpha off with -flatten (for a single image)
OR use -bordercolor white -border 0

See Removing Transparency
http://www.imagemagick.org/Usage/masking/#remove

OK... if I understood you and the link right, this should work correctly:
And what flatten concerns... I tried it out just before posting in this forum and had some funny results, because I had a multipage pdf file to convert and I think you can imagine what had happend to that file

Thanks a lot again for the help.

Glad to see it worked out. We are glad to help any way we can.