Graphic Format Support

[snoopy]

Does the PNG graphic format support 'layers'?

[gplasky]

PNG
Name Means: Portable Network Graphics

Benefits
16-bit/channel support - Software support for 16-bit/channel PNGs is rare. 8-bit/channel support is more common.
Alphanumeric transparency - Transparencies can fade from fully transparent to fully opaque
Gamma Correction - allows the image to retain the same brightness across any platform
Lossless compression
Open-Source format - No licensing is needed to support the format. It's freely available for use.

Disadvantages
No ICC profile support - As I was writing this, I noticed something a bit odd. The PNG spec states it only supports either the sRGB or iCCP color space and Photoshop 7 will not allow ICC profiles to be attached to a PNG (through Save As...). However, if the profile is assigned or it's converted to a profile, and then saved (Ctrl+S), the profile is preserved. Although I'd say ICC support is sketchy at best (perhaps just a fluke with PS), it is certainly something to look into.
No EXIF data support
The compression algorithm (called "zlib") is complicated and thus it's slower to save than other formats.
16-bit/channel support in editing software is limited.
No multi-layer support

Gerry

[snoopy]

gplasky.... You ROCK man!

That's awesome info.

What is "icc profile" ?

[Opus4]

Originally Posted by snoopy

What is "icc profile" ?

Just how much do you want to read? Do you really want links to fully explain profiles and their usage? Essentially, a profile is a lookup/conversion table that gives meaning to the color data in an image file. By itself, an (RGB) value of (34,56,127) has no real meaning, except that it seems to mix some amount of Red + Green + Blue. By including a profile with that color data, you give it real meaning by providing a color space where those values reside, so you can tell exactly what that color should be.

... or at least you give it real meaning for an application that uses profiles to make sure the colors are displayed correctly, when displayed on a calibrated & profiled monitor or printed on a profiled printer. The profiles come into play for color-critical work, such as digital photography and any other image manipulation where you want to accurately control the color.

So, for the RGB values I showed above, that color will appear differently in PhotoShop, depending on what profile is assigned to the image. BTW: Internet Explorer on Windows and SageTV are not color managed, meaning they don't make use of any profile included in an image file.

Edit: Lots of color data on Bruce Fraser's site, including a Color Vocabulary.

Aren't you glad you asked...

- Andy

[snoopy]

That really is outstanding. I just bought an epson printer so that I could use a continuous ink system (by an eBay outfit named jlwsales). He mentioned emailing me a profile. So yes, the basic info you provided is very helpful to me in understanding that. I completely understand now why such disparity among print/screen images. The most obvious problem I see is lighting. Backlit appears different than projected light but I always had a feeling there was more to it than that. Thanks so much for that description.