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Transparency usage story
Posted: 2012-02-28T23:47:09-07:00
by Janek
Hi,
After long inactivity on ImageMagick I've upgraded binaries to ImageMagick-6.7.54, and I saw that some commands works different. Problem was with transparencies.
I've solved problem and now I can show you story of changes in transparency usage.
If you just want to put coloured text on transparent background, and save image to png you need:
before ImageMagick-6.5.23-Q8:
Code: Select all
convert -background transparent -pointsize 55 label:"test" outputPNG32.png
ImageMagick-6.5.23-Q8
Code: Select all
convert -background transparent -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
ImageMagick-6.7.54-Q8
Code: Select all
convert -background transparent -virtual-pixel background -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
Have you simpler and more version independent way for this task?
Re: Transparency usage story
Posted: 2012-02-29T00:04:20-07:00
by anthony
Janek wrote:Hi,
After long inactivity on ImageMagick I've upgraded binaries to ImageMagick-6.7.54, and I saw that some commands works different. Problem was with transparencies.
I've solved problem and now I can show you story of changes in transparency usage.
If you just want to put coloured text on transparent background, and save image to png you need:
before ImageMagick-6.5.23-Q8: convert -background transparent -pointsize 55 label:"test" outputPNG32.png
ImageMagick-6.5.23-Q8 convert -background transparent -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
ImageMagick-6.7.54-Q8 convert -background transparent -virtual-pixel background -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
Have you simpler and more version independent way for this task?
I don't understand your need for the virtual-pixel setting (highlighted above).
Virtual pixels are used in operations such as blurs, convolve, morphology, distortions, and some FX user functions, where images are being referenced outside their normal 'real' boundaries.
See
http://www.imagemagick.org/Usage/misc/#virtual-pixel
Re: Transparency usage story
Posted: 2012-02-29T00:24:39-07:00
by Janek
I don't know meaning of virtual-pixel operator. I'm don't understand too why this work, but example from ImageMagick-6.5.23-Q8 doesn't work in ImageMagick-6.7.54-Q8.
I'm just guessing how bring transparency and saw that virtual-pixel helps.
See that
Code: Select all
convert -background transparent -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
doesn't produce transparent background in ImageMagick-6.7.54-Q8 and newer.
maybe this is bug
Here is comment for 6.7.5-4
Code: Select all
2012-02-08 6.7.5-4 Cristy <quetzlzacatenango@image...>
* Set image alpha channel for -virtual-pixel background and transparent.
* Get tiff:fill-order as an image artifact, not an image option.
p.s. thank you for fast reply
Re: Transparency usage story
Posted: 2012-02-29T08:22:43-07:00
by glennrp
Janek wrote:
Have you simpler and more version independent way for this task?
Instead of
Code: Select all
... -define png:color-type=6 outputPNG32.png
you can just write
Re: Transparency usage story
Posted: 2012-02-29T18:49:21-07:00
by anthony
Janek wrote:See that
Code: Select all
convert -background transparent -pointsize 55 label:"test" -define png:color-type=6 outputPNG32.png
doesn't produce transparent background in ImageMagick-6.7.54-Q8 and newer.
maybe this is bug
Yes I would say this is a bug...
I can confirm that the lable comes out all black
Code: Select all
convert -background none -pointsize 55 label:"test" -verbose info:
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...
Format: LABEL (Image label)
Class: DirectClass
Geometry: 90x63+0+0
Resolution: 72x72
Print size: 1.25x0.875
Units: Undefined
Type: Bilevel
Base type: Bilevel
Endianess: Undefined
Colorspace: sRGB
Depth: 16/1-bit
Channel depth:
gray: 1-bit
alpha: 1-bit
Channel statistics:
Gray:
min: 0 (0)
max: 0 (0)
mean: 0 (0)
standard deviation: 0 (0)
kurtosis: 0
skewness: 0
Alpha:
min: 65535 (1)
max: 65535 (1)
mean: 65535 (1)
standard deviation: 0 (0)
kurtosis: 0
skewness: 0
Colors: 1
...
Alpha is present, image it should be black with variable alpha but it is totally opaque!
Definatally something is wrong. -- reporting
Re: Transparency usage story
Posted: 2012-02-29T20:03:54-07:00
by glennrp
I used IM 7.0.0-0 2012-01-02 Q16 and it looks fine. However, using IM 6.7.5-8 Q16 (svn r 7001) it's just a black image When I use .txt format instead of .png it still behaves the same, just a black opaque image. The bug seems to be in the "label:" format, not in the PNG format.
Re: Transparency usage story
Posted: 2012-03-05T01:24:54-07:00
by Janek
Hi,
I've seen that in new ImageMagick-6.7.5-9 works fine. In changelog is mentioned that bug is fixed in ImageMagick-6.7.5-8.
thank you for fixing
Re: Transparency usage story
Posted: 2012-03-06T00:47:18-07:00
by anthony
Yes confirmed. It is now working again. IM v6.7.5-9