PNG File format?

[hkellogg]

Immediately after I told students that the three main file formats for print production are .EPS, .TIF, and .JPG, (and .jpg is the least desirable) I had a student as why PNG wasn't an acceptable file format.

I know it isn't and I answered that the RIP process doesn't support .PNG; that it is mainly for web. However, I wasn't truly sure why it cause problems.

Can anyone provide a more definitive answer?

Thanks

Hans

[steve.weiss]

The reason that I find not to use a PNG is that it can not be in a CMYK color space (Checkd in Photoshop). I ran a test with an RGB PNG through my work flow (flexo printer) placed RGB PNG into Illy with some type saved to PDF imported PDF into ArtPro, Trapped, ect Export normalized PDF to FlexRIP server get a fine looking output file.

My reasoning would be to use a format that can support CMYK so the printer is not left making guesses on what an RGB image should look like.

Cheers.
Steve

[John Clifford]

PNG was originally a format that was developed (if memory serves correctly) when Compuserve threatened to sue Adobe over their GIF format. Adobe created the PNG format as an alternative. While not directly indexed color (by then there was little need to use Indexed color), the format is optimized for web output.

As stated, it is an RGB format and not CMYK so is not a good fit for printing. However, as we're moving toward RGB workflows, it's less of an issue than previously.

[tobias]

Most recent rips should be able to handle PNG; for instance the HP Production Pro Print environment (which comes with HP Indigo 7000 installations and several other HP machines) RIPs it just fine. It's just that it doesnt support colorspaces that are 'appropriate' for press that it wouldn't be 'suitable'. On the other hand, especially if you have a clueless customer that wants to run an ad with text, I'd prefer a RGB PNG over a RGB JPEG any day. (yes you should ask for a proper PDF. I said clueless, didn't I?)

[claude72]

Immediately after I told students that the three main file formats for print production are .EPS, .TIF, and .JPG, (and .jpg is the least desirable)

Better told your student that today, the 3 main file formats for pixels pictures are PSD, TIFF and PDF...

... and especially teach them that Photoshop EPS is "out of age" at least since Quark released XPress 6 (2003!!!)... and had already more inconvenients than advantages even in the old times of XPress 3, 4, or 5, except for some special cases.
Today, as a basic rule, you can consider that PDF can do all what EPS did, and often better!...
... meaning that today the PhotoshopEPS has to be used only in some rare special cases (for example clipping mask or duotone pictures for QuarkXPress 5 or older... or spot color in a Photoshop picture using DCS format) and has lost it's first place in the "Top 3" of the Print file format (first place that it had got by accident!!!).

JPEG is IMHO a dangerous format, because it is mainly a web/office file format, and it's either crap or potentially crap... but in some cases with all the needed knowledge and all the needed cares to use it, JPEG can be an helpful Print format.

But JPEG can also be the uglyest file format! so, once you accept JPEG as a Print format, and you accept the (risks of the) known problems of the JPEG, why not accept also all the others web and office file formats, like PNG, BMP, GIF, with all their risks and limitations, knowing than none of these 3 web-formats can become as ugly than a low quality JPEG re-recorded 20 times???
BMP is nothing more than "Microsoft's TIFF",
GIF, even with only 256 colours is less ugly than a low quality JPEG,
and a PNG file is a picture with pixels and can be imported in XPress!

[Lukas Engqvist]

Risk of PNG is that it is sometimes colour managed. I had a job where the customer wanted to have pictures with transparent backgrounds and soft shadows, also file size was an issue. PNG was a very effective format, only as long as you work in an environment where the colours are synced accross applications and your output is a PDFX1 (converted to CMYK) or PDF4 (with propper colour management definitions) you will get good results.
The PNG files were looking different on different computers, and it turned out that even though the files had an embedded ICC, wich meant they were consistent in Photoshop, (where ICC was taken in) in InDesign (where ICC was ignored) they were dependant on the RGB settings of the program. RGB workspace, rendering intent and/or if blackpoint compensation was implemented makes a big difference.


A PNG will not in CS4 read the ICC profile attatched to it, your RGB workingspace will be used. In the print PDF you do not have PNG anyway, it is a transitional format. That it is not able to support CMYK is an argument i find thin…*why would I need it to support CMYK, that it doesn't maintain ICC profiles is a problem.
I would suggest if you want to use PNG and you have made the decision that all files with no ICC is sRGB, using PNG as sRGB files will give you good results and wouldl be an acceptable workflow.

[rich apollo]

The only real problem with PNG is that the bit depth is variable. So, you can end up with PNG files that are actually indexed color. It's not a 'problem', but a consideration when the PNG file is being generated.

I can't find it right now, but it seemed like in the original PNG specification there was no support for ICC profiles. If memory serves, images could be sRGB or not sRGB. Those were the choices. I think that has changed, though.