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saving PNG's in photoshop

saving PNG's in photoshop

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Yaral

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  • Joined: 13 Oct 2006
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Reply with quote Post Posted: Fri May 09, 2008 02:00
I've been running into a problem while trying to save a large PNG file with PS (CS3). Using save for web, if I choose PNG 8-bit, I do not get true transparency. I get rough transitions similar to saving as a gif. However, if I save as a 24-bit PNG, I get a large file size (700k).

Does anyone have experience using PNG's? If so, how do you go about saving them?

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karmedic

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Reply with quote Post Posted: Mon May 26, 2008 17:52
24bit PNGs support alpha transparency whereas 8 PNGs do not. Since you are saving 8 bits per channel in the 24 bit PNG (and then another 8 bits for the Alpha) the file size will be alot bigger - ie, it's true colour. The trade off with an 8 bit PNG is that a) you get flat transparency and b) you are restricted a 256 colour palette. I will typically only use 24bit PNGs if I require true alpha transparency ... if not i got with another format. For a large image that has many colours and does not require alpha transparency i will typically use JPEG and adjust the lossiness to suit my needs.

hth

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objx

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Reply with quote Post Posted: Tue May 27, 2008 09:01
Remember that 24-bit PNG's isn't supported in IE6 browsers too.(the background gets colored)
There is a javascript-solution for IE6. This will fix the transparency problem, but it's quite alot of code, just to get the transparency working:
http://www.twinhelix.com/css/iepngfix/
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Bill Posters

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Reply with quote Post Posted: Tue May 27, 2008 11:11
objx wrote:
Remember that 24-bit PNG's isn't supported in IE6 browsers too.(the background gets colored)
There is a javascript-solution for IE6. This will fix the transparency problem, but it's quite alot of code, just to get the transparency working:
http://www.twinhelix.com/css/iepngfix/


Js solutions simply automate the application of a CSS-based solution.
For more control and for fewer instances, simply apply the CSS fix manually via an IE stylesheet.

e.g.

styles.css
#something {
   background: url(/images/bg-something.png);
}

ie-5-6.css
#something {
   background: none;
   filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src="/images/bg-something.png");
}

IE filtered background images won't tile, so you may need to use an alternative version of the image, large enough to span the desired area.

e.g.

styles.css
#something {
   background: url(/images/bg-something.png);
}

ie-5-6.css
#something {
   background: none;
   filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src="/images/bg-something-large.png");
}
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