how to get smooth resize?

[linjuming]

orignal btn.png


description:

[fmw42]

try including the alpha channel in your resize

convert image -channel rgba -resize .... result

[linjuming]

the same result

[fmw42]

Also try a different -filter option with -resize

see http://www.imagemagick.org/Usage/resize/

or try -distort SRT

see http://www.imagemagick.org/Usage/distorts/#srt


Otherwise, you may have to "feather" your alpha channel separately.

see
http://www.imagemagick.org/Usage/antialiasing/
http://www.imagemagick.org/Usage/masking/#difference

[anthony]

The problem looks like it is your PNG display program not displaying semi-transparent colors,
but only boolean transparency (such as for BMP and GIF images.

Try removing the transparency from the image, replacing it with some color (matching background)
http://www.imagemagick.org/Usage/masking/#remove

These are your only solutions, though the GIF semi-transparency handling goes into some methods
of mixing edge anti-alias colors with boolean transparency for use on patterned or light/dark/grey backgrounds
http://www.imagemagick.org/Usage/formats/#bgnd


Also as you are generating multiple images look at
Writing an Image, Multiple Time
http://www.imagemagick.org/Usage/files/#write

[linjuming]

Point Hermite Cubic
Box Gaussian Catrom
Triangle Quadratic Mitchell


Lanczos Hamming Parzen
Blackman Kaiser Welsh
Hanning Bartlett Bohman

i test all filter ,the result are all not good.
ps ,the png is save form photoshop , and the descriptsiotn png is cut from ie6 ,show it has blue background.

[fmw42]

My tests look fine on IM 6.7.3.0 Q16 Mac OSX Tiger

The image under the alpha channel is not too smooth, but the alpha channel is smooth.

convert btn.png -resize 28x28^ btn28.png



convert btn.png -resize 36x36^ btn36.png



convert btn.png -resize 52x52^ btn52.png



Perhaps try upgrading IM and libpng. Anthony may be right that your alpha channel is not being kept as 8-bit, but is getting converted to binary.

[anthony]

Perhaps try upgrading IM and libpng. Anthony may be right that your alpha channel is not being kept as 8-bit, but is getting converted to binary.

Actually I said that the application displaying the image is probably not displaying the alpha channel properly!

I have a feeling that some of the smaller PNG images are being saved using an 8-bit PNG palette with full semi-transparency capability. This is something that was only recently added to the PNG coder (thanks Glenn). Only happens when the actual color count (including semi-transparency) is less than 256.

Palette PNG's are typically limited to boolean transparency only (IM itself limits it to boolean transparency (like GIF) if PNG8 format is requested), so it may be that your display application thinks that all palette PNG images only has boolean transparency, and is thus displaying them incorrectly.

One solution to 'fix' the PNG, just for the display application, is to use PNG32 format, or one of the many PNG coder settings to ensure a palette sub-format is not used.
http://www.imagemagick.org/Usage/formats/#png_write

[linjuming]

Seems png32 is best.
Thank you !

[fmw42]

In principle, it should not matter if PNG32 or PNG8 with transparency, if you are using the latest version of IM. My test above worked fine without specifying PNG32: and maintained your pseudocolor transparent png format.

You never say what version of IM you are using? Nor what version of libpng.

Note that the PNG developer has made many changes and improvements to the PNG functionality over quite a number of releases. First consideration when using PNG is to be sure you are using the latest version of IM.

[linjuming]

i used
ImageMagick-6.7.0-9-Q16-windows-dll.exe
before.now i update to
ImageMagick-6.7.3-1-Q16-windows-dll.exe
but still the same result with old version.

[fmw42]

Must be a windows issue as Unix and Mac do not seem to have that problem. Or perhaps it is your libpng that needs upgrading.

[anthony]

Earilier versions of IM would have output the image as PNG32. It is only recent IM's that handle semi-transparency palatte (indexed) PNG images.

I doubt your IM is going wrong, your PNG images are probably correct.

It is more than likely it is only your PNG display program that is mis-handling index PNG images. the screen shot says PHP, and I know that most PHP image processing is done using the "gd" library, which is very ancient and very likely to be miss handling indexed PNG with semi-transparent colors. A mode that was only later added to PNG sub-image format.

You are only giving use a screen shot of the 'displayed' image, not the actual problem image, as such it is impossible for us to say for certain that the images generated is correct or not. Can you publish the actual generated images?

Otherwise you can check the actual image sub-format using identify -verbose


For example....

Code: Select all

convert btn-1.png -resize x20^ little.png
identify -verbose little.png | grep Type:
  Type: PaletteMatte

Which showed that MY version of IM did generate a indexed or palette PNG image, just as I suspected!
The image is correct and displays correctly without edge aliasing effects.

I really think it is your display program (written in PHP) that is at fault not IM.

[linjuming]

Image: little.png
Format: PNG (Portable Network Graphics)
Class: DirectClass
Geometry: 54x20+0+0
Resolution: 72x72
Print size: 0.75x0.277778
Units: Undefined
Type: PaletteMatte
Endianess: Undefined
Colorspace: RGB
Depth: 8-bit
Channel depth:
red: 8-bit
green: 8-bit
blue: 8-bit
alpha: 8-bit
Channel statistics:
Red:
min: 0 (0)
max: 93 (0.364706)
mean: 24.7565 (0.0970842)
standard deviation: 10.199 (0.039996)
kurtosis: 3.84442
skewness: 1.31031
Green:
min: 0 (0)
max: 185 (0.72549)
mean: 102.177 (0.400694)
standard deviation: 44.2577 (0.17356)
kurtosis: -1.00124
skewness: 0.205439
Blue:
min: 0 (0)
max: 255 (1)
mean: 207.85 (0.815098)
standard deviation: 43.5392 (0.170742)
kurtosis: 8.16684
skewness: -2.65481
Alpha:
min: 0 (0)
max: 255 (1)
mean: 239 (0.937255)
standard deviation: 52.3219 (0.205184)
kurtosis: 11.9866
skewness: 3.54869
Image statistics:
Overall:
min: 0 (0)
max: 255 (1)
mean: 87.6958 (0.343905)
standard deviation: 40.9146 (0.160449)
kurtosis: 33.9294
skewness: 5.79701
Alpha: rgba(65,65,205,0) #4141CD00
Colors: 131
Histogram:
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Rendering intent: Undefined
Interlace: None
Background color: white
Border color: rgba(223,223,223,1)
Matte color: grey74
Transparent color: none
Compose: Over
Page geometry: 54x20+0+0
Dispose: Undefined
Iterations: 0
Compression: Zip
Orientation: Undefined
Properties:
date:create: 2011-10-12T12:30:15+08:00
date:modify: 2011-10-13T15:21:50+08:00
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PNG:tRNS : chunk was found
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User time: 0.000u
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Version: ImageMagick 6.7.3-1 2011-10-12 Q16 http://www.imagemagick.org

[linjuming]

finally i find where the problem come from.
it is the terrible bug of ie6 ,when i change to ie7 or firefox ,there is no problem at all.