Alpha channel is reversed when creating ICO files
Posted: 2008-10-01T21:13:24-07:00
There is a problem with alpha channels when creating ICO files. The alpha channels are being reversed. The problem is discussed in this thread, starting with the 8th post. In particular, see anthony's post on page 2, as he has created a test case. I'll quote him here:
I wasn't able to follow the instruction he gave in this post, as I am not that great of an IM guru.anthony wrote:If it is then yes. With (small) examples if posible,
Idealy something likeShould return '0' as in there are no color differences between a PNG and a ICO image.Code: Select all
convert image.png ico:- | compare -metric PNE ico:- image.png null:
However that does not gurantte the image, as it only checks a write and read, reproduces the original image exactly. As such a quick eyeball look may still be needed. But it does provide a quick automated check that the format is working reasonably well.
My own test shows the images are totally different, and a eyeball test...shows the write-read cycle has indeed inverted the alpha on my IM v6.4.4-2 svn build.Code: Select all
convert image.png ico:- | display ico:-