Legacy ImageMagick Discussions Archive

Hi Everyone

I'm working with images that were created as monochrome TIFFs (colour separations) where I need to convert them to PNGs with a transparent background, removing all the white.

The problem is, the images have gradients in them. So for example I need to be able to replace not just solid white with transparent (which I managed to do already) but also take into account percentages; so for example what was 40% black before would become 100% black but 40% opaque, if that makes sense.

So an example of the source image:
https://www.dropbox.com/s/zy5by7duftpj0 ... t.tif?dl=0

Desired result:
https://www.dropbox.com/s/55hf82swzg3mj ... 1.png?dl=0

Looking for recommendations as to how this could be achieved with ImageMagick (I am actually using Magick.NET but guess this is more a question of the correct technique to achieve).

Thanks in advance.

Your gradient.tif has two images, both CMYK with a profile. I'll take the first image, and convert it to sRGB.

The magickal incantation is "-alpha copy", which copies the grayscale into the alpha channel. Because we want what was white to become transparent, we need to negate. The result is entirely black, but with varying transparency. Does that do what you want? Sorry, I don't know Magick.NET.

Hi there, thanks for the reply!

When I run the command though I get an error message:

convert: unable to open image `sRGB.icc': No such file or directory @ error/blob.c/OpenBlob/2675.

I figured this was due to the icc profile argument needing a full path to be specified. There did not appear to be any such profile in the ImageMagick files though so I downloaded one from the ICC website. However pointing to that a new error is thrown:

convert: Incompatible type for "RichTIFFIPTC"; tag ignored. `TIFFFetchNormalTag' @ warning/tiff.c/TIFFWarnings/852.

Regards
David

There may be a copy of sRGB.icc in the directory you installed ImageMagick in. Sorry, I should have said.
That's just a warning. Don't worry about it. Is the result what you want?

Ah sorry, I thought it had failed - you are right it had converted the image fine! Yes that was exactly what was needed, thanks a lot - magick indeed!

Those warnings come from TIFF tags that are custom and for which IM knows nothing about them.

In your commands, you can avoid getting them by adding -quiet right after convert (or magick in IM 7).