1. Your source image is a 256-color palette image. If you resize any image, by default the output will be in truecolor aka 24 bit color aka 8 bits per pixel. You must quantize the image down to 256 colors. This commandline resizes and quantizes, giving an output of 52,209 bytes:
convert -resize 426x320 -dither -colors 256 -depth 8 source.png resized.png 2. For even more compression, you can turn to pngcrush, not part of imagemgick but a separate package. pngcrush applied to resize.png gave me an output of 49,905 bytes. 3. Both convert and pngcrush will preserve the transparency in this case. On Fri, Apr 25, 2008 at 3:31 AM, Joel Poloney <[EMAIL PROTECTED]> wrote: > I've been banging my head against this all night and can't come up with any > solution. I'm trying to take a PNG image, resize it, and compress it (if I > can). The PNG image I'm working with has transparency. You can find it > here: > http://joel.poloney.com/source.png. I have imagemagick version 6.2.4. > > The source png is 85kb. If I run the command "convert -compress JPEG > -quality 80 source.png output.png", the output.png is about 118kb. > Obviously, that didn't work. Say I want to resize this image down before I > compress it. The original size of this is 600x450. If I run the command > "convert -resize 426x320 source.png resized.png", the resized.png is about > 150kb. Why is my image smaller pixel-wise and bigger file-size wise? > > I then began experimenting with image masks. I figured, if I could extract > out the alpha channel into a 8-bit mask.png ("convert source.png -channel > matte -negate -separate -depth 8 -type Grayscale mask.png"). I then > converted the png to a jpeg and compressed the jpeg. I finally composed the > two back together with the "-compose Copy_Opacity" option, and it works... > but the file size is enormous. > > If I use the original source png in Flash CS3 and create a simple movie > with > 1 frame (the source.png), and export it (with a jpeg compression of 80), > the > resulting swf is 37.1kb. They're doing some kind of compression and I can't > figure out what it is and why it's not working with imagemagick. > > Any suggestions? > > Thanks, > > -- Joel > _______________________________________________ > Magick-users mailing list > [email protected] > http://studio.imagemagick.org/mailman/listinfo/magick-users > Greased Lightbox <http://shiftingpixel.com/lightbox/> →←+-↻ Loading image Click anywhere to cancel Image unavailable Greased Lightbox <http://shiftingpixel.com/lightbox/>→←+-↻ Loading image Click anywhere to cancel Image unavailable
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