Legacy ImageMagick Discussions Archive

hi,

I installed latest versions of Imagemagick(cygwin version) and cygwin(while installing i have installed the imagemagick and perlmagick packages also). the problem i am facing is im unable to get the "alpha extraction" for the images. it is showing an error message "unrecognised alpha extraction".

when i used the command "identify -verbose <image.png>" then in the details of the image there are only RGB and no alpha .
TELL ME WHICH VERSION OF CYGWIN SUPPORT ALPHA EXTRACTION IN IMAGEMAGICK?

so please tell how to resolve this problem......It is really very important for me?

post a link to your png image so others can look at it to see if it has an alpha channel.

What version of IM are you using? There have been problems with PNG being updated for many release, but it should be pretty solid in the current release!

not only for png file... I am facing the same problem with other image formats also.

here is the link of an image for which i have tried
http://img51.imageshack.us/img51/2554/ndjcdsiovb.jpg

Your image has no alpha channel as it is jpg. Jpg does not support alpha channels or any transparency.


identify -verbose ndjcdsiovb.jpg
Image: ndjcdsiovb.jpg
Format: JPEG (Joint Photographic Experts Group JFIF format)
Class: DirectClass
Geometry: 240x320+0+0
Resolution: 96x96
Print size: 2.5x3.33333
Units: PixelsPerInch
Type: TrueColor
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
red: 8-bit
green: 8-bit
blue: 8-bit
Channel statistics:
Red:
min: 8 (0.0313725)
max: 232 (0.909804)
mean: 133.878 (0.525011)
standard deviation: 53.7727 (0.210873)
kurtosis: -0.0286849
skewness: -0.654271
Green:
min: 9 (0.0352941)
max: 239 (0.937255)
mean: 132.806 (0.520808)
standard deviation: 57.8365 (0.22681)
kurtosis: -0.577086
skewness: -0.391421
Blue:
min: 8 (0.0313725)
max: 241 (0.945098)
mean: 133.657 (0.524145)
standard deviation: 56.5328 (0.221697)
kurtosis: -0.454569
skewness: -0.348572
Image statistics:
Overall:
min: 8 (0.0313725)
max: 241 (0.945098)
mean: 133.447 (0.523321)
standard deviation: 56.0729 (0.219894)
kurtosis: -0.372293
skewness: -0.455871


Post a link to a png or gif image with transparency? And post your exact command line.

is that ok if i convert this jpg file into png and send you that image?????

sin wrote:is that ok if i convert this jpg file into png and send you that image?????

No, because it still won't have an alpha channel. If you issue is extracting a meaningful alpha channel from an image, then you need to upload the image that actually has that alpha channel in it. You can always enable an alpha channel in a png file, for example, but it will be either all transparent or all opaque (see -alpha transparent and -alpha opaque). But those kinds of alpha channels are likely not what you had in mind.

Here is one way to get a png file with some kind of alpha channel that has some meaning.

convert logo: -transparent white logo_trans.png

Can you extract the alpha channel from this image?

convert logo_trans.png -alpha extract logo_trans_alpha.png