Print Issues: Gradients, Banding, Dither and Colour Profiles

[druma]

Hi all,

I've recently encountered a problem with a printed piece of work - a potential problem I've always been aware of, but have never experienced first hand. The piece I had printed contained a large area of sky, with subtle changes in colour. There are a couple of areas where there is a very small change in colour, spread over a relatively large area. When I viewed the document on screen there was some very subtle banding, but I had to zoom in close to see it. When viewing the document at actual size, it wasn't noticeable at all. When I had it printed (digitally), the banding showed up really badly. Part of the problem came from the discrepancy between the colour profile of the PDF (CMYK Euroscale) and whatever the colour profile of the large format inkjet printer might be. Besides the banding, the colours were over saturated and the whole thing was too dark as a result. I compared the CMYK strip in the slug to a Pantone process guide and it was pretty far out. So....... my first question is, Is there an easy way to make my work print better on a digital printer? Can I download filters to apply to images that will compensate for the difference between Pantone offset litho and a particular digital printer? I had thought about having a test page printed - with blocks of colour spread across the CMYK gamut - and then comparing them with a process guide and maybe creating a filter, or possibly recording an action in Photoshop to compensate. Does that sound like an idea?

The second cause of the problem was the gradients I'd used in the image. They were created outside Photoshop, and I hadn't applied dither. I've now added some noise to the sky, which appears to have solved the problem, but my second question is, what is the best way to deal with this problem? When I apply dither to a gradient in Photoshop, sometimes it doesn't seem to make a great deal of difference. Adding noise works, but I just wondered if there was a way to edit the level of dither. I'm working on another design at the minute, and it looks like it may well involve lots of gradients, so I'm keen to find the best way. Also I've read that it's best to apply noise to a gradient after the image has been converted to CMYK (assuming you're working in RGB to start with) because it will have greater affect. Obviously, on a lot of occasions that simply isn't an option. I've posted some jpgs to illustrate what I'm talking about.

Thanks for bothering to read this.

druma


Original PDF
http://img293.imageshack.us/img293/8896/ggpdfzr2.png (http://imageshack.us)


Scan of printed poster
http://img490.imageshack.us/img490/6858/ggscanob0.png (http://imageshack.us)

[rickself]

Well, druma, it sounds like you're somewhat aware of what's going on. Adding noise is my choice of smoothing the background.

My only concern is why you're saving as pdf and what level of pdf you;'re using.

In our offset shop I always prefer native files over pdf but each shop is different, particularly in the digital realm. The majority of people don't know how to create a pdf.

Being that it is Sunday so others will have more knowledge in here come Monday.

[PrintDriver]

Are you doing the printing or are you sending it out?

Large format and gradients is always going to be a problem. If at all possible the gradients should be done in Photoshop and added as a LINK to a native format layout document. That way if color needs adjusting it can be done. Even then, there are some color combinations that band even in Photoshop. Light blue to white is one of them. (Green to Yellow is another.)

If you are doing the printing yourself you have to be really careful of profiles. Even a change in the temperature or humidity of your shop can have an effect on the final print so it's tough to tell where you are going wrong.

If you are sending this out to be printed, most large format vendors require files to be in Native format so they can apply their own profiles and color spaces. Some even require RGB color spaces. When sent a PDF, you basically get what you get. Even with Pitstop it isn't always possible to adjust the profiling/color to what needs to be done - and not all shops have Pitstop. Someplace like a quickyprinty place probably doesn't even know what Pitstop is...<sigh> The shops that do, don't always use it because it blows the production schedule if the requested turnaround time is tight.

Proofing is ALWAYS recommmended for a large format piece. After all, there is nothing more expensive than a large bad print. Anything can go wrong with color. It is also a really good idea to call and talk to the vendor, or better, the tech, and find out exactly what has to be submitted in what dpi and in what format to ensure a decent outcome.

When doing large format, throw your Process book in a desk drawer. The Bridge or the Solid to Process guide are absolutely useless in large format printing. Work with Pantones (coated or uncoated as specified by the vendor) in 100% tints and pay the upcharge for matching. Or ask for a chart (if the vendor works that way).

Large format is not like plate printing. Every medium/printer/inkset will print a PMS color differently. By starting with a known value a vendor can usually match or come very close to the intended target (within gamut) using his own profiles or color management system. That is why unflattened Native files are best.

[druma]

Thanks for the advice.

Basically I think I need to use a different print shop. I called them on the phone - before sending the file - and they seemed pretty vague. They weren't too bothered about what kind of file I sent. I thought PDF would be best so that they couldn't alter the original - although I suspect they wouldn't have done anything about the problem anyway. Obviously I need to find someone who'll pay attention to these things. I think this print shop was more familiar with printing cheap fliers and take-away menus.

Anyway, lesson learned, although I hate it when learning a lesson costs me money. ;)

Thanks again