Discussion: OCAD Overprint Effect

ISOM recommends for 4-colour offset printing, the use of "overprint effect". Though we use digital printing, a lot of maps use the default OCAD colour tables, which have "overprint effect" switched on for a number of colours. Although not visible in OCAD, this seems to put overprint code into the generated pdf. Has anyone had any unexpected effects when viewed or printed from Adobe Reader? Or non-WYSIWYG effects at a print-shop?

The only really safe way to deliver a pdf to either a print shop, or an end user to display on their screen and ensure that all overprint effects are displayed the way you want is to use an older pdf standard as your baseline, and flatten all transparency. That means to take every place where there are two overlapping colors and one of them is set to multiply as its transparency effect instead of knocking out the lower color completely, and break out that area as a separate polygon with a color that has been pre multiplied. That makes sure the rendering device only needs to read simple cmyk colors for each polygon from the pdf.

I have had problems with different version of acrobat improperly displaying non flattened pdfs, especially with scattered tree areas.

To accomplish this, instead of relying on OCAD to produce proper pdfs, I export all my maps as spot color separated eps files, and recombine them in Illustrator to a file that has a layer for each spot color. Then I can either flatten the file for delivery, or keep out a color if it will be spot color printed. I have had really good results by doing CMYK+Brown digital offset printing. Then I deliver a pdf that has had all the colors except brown flattened, and leave the brown as a spot color.

You have to be careful in setting up how you want the overprint to be done though, as its not exactly like the real effect from layering spot colors. If you overdo it it doesn't look good. The minimum that I do is to always overprint the purple course info, so that you don't knockout all that important detail under the circles, lines, and numbers, and to overprint the brown. The effect that the brown gives when crossing green patches makes the map a lot more readable, and I have found that it eliminates the yellow halo that sometimes appears around brown in green. Blue and green in yellow can also work well, but blue in green doesn't have enough contrast and should be set to knockout.

Sorry Ed, my eyes glazed over when I got to "flatten all transparency" and the lack of interest suggests others may have too. I think the standard process ought to work, I just want to take "File..New" in OCAD, draw a map, and use OCAD's "Export..PDF" to send a map to my print shop. And also to non-orienteers such as teachers, permanent course users etc.

Would someone care to do this with a simple map consisting of a yellow blob with a stream running through it. And perhaps a lazy-man's pond in the middle (ie no cut-out). Export a pdf. Print the pdf from Adobe Reader (on your home printer, for now). Are green streams and ponds a peculiarity of my computer? Perhaps its living upside down.

I haven't tried export pdf's for ages but for the example you are giving (blue in yellow) have you tried putting zeros in the 'yellow' column of the 'spot colors %' part of the color table for all the blue colors (100% 75% etc). That solves the problem of blue under yellow appearing to be green in 'spot color view'. Whether that has any effect on pdf's I dont know.

Yes. Can't remember the exact details but ...
Using the OCAD-supplied template for ISSOM, we found the grey wall had a transparency on it. When printing at home, or viewing the pdf, walls in open yellow looked like 50% grey, as they should. When we got the final product, the transparency made the walls considerably darker grey, such that many people misread them as "uncrossable".

Probably you should turn off "Transparency" in OCAD rather than trying to edit the pdf.

There are two effects operating here:
- colours defined in OCAD as overprint
- PDF software honouring the overprint setting
If you don't want to switch off the overprint effect in OCAD, you could try doing it in Adobe Reader (version XI) :
Edit/Preferences/Default Transparency Blending Color Space /Working CMYK

The Edit/Preferences/Use overprint preview/Always option will show you what colours have overprint effect. To see what it will look like with overprint switched off select the Never option.

Seems to me that if your eyes are going to glaze over when it comes to a good quality output, maybe you should transfer that part of the job to somebody who knows what they're doing. The map and its legibility is the part of an orienteering event that actually matters. I've lost patience with events that refuse to bother trying to get a decent-quality map in my hands.

On the other hand, we have computers now, and you'd hope that they've advanced us beyond the days when there was a select priesthood who were able to print maps. If it's hard, then the software is deficient. gruver's points are well-taken, starting with, "I think the standard process ought to work". He does want to print quality maps, but without obscure technical black magic.

Thanks JJ. Working on a simple statement suitable for those who know less than me. The circumstances in which the problem may occur, and what to do to prevent it. A short clear statement is harder to compose than a lengthy one.

A short clear statement is harder to compose than a lengthy one.

That's pretty much a potted history of orienteering, right there.

Last fall I was certified by NOF (i.e. Haavard Tveite, the IOF Map Commision leader) as a map/course printer:

I do it the easy way, i.e. printing directly from OCAD to a locally attached high-end color laser printer, and it still took me a couple of months to get everything right, with good paper, calibrated spot colors and correct overprint effects.

Going via OCAD-generated pdfs does not work, you have to be in Draft View in order to get overprint, and in that mode pdf generation is disabled.

I can't remember ever having any serious problems caused by map being laser printed without overprint effect. Blue ditch has always same tone of blue both in green and white forest, brown contour is same brown tone everywhere, cliffs in green can be spotted because contours are not any darker, dotknolls in green will not get mistaken as boulder because they are brown, not a darker overprint version of it. Even if it does not look like an offset printed map it is well usable and objects are easy to identify because tone is always the same. But I do have seen several only barely usable maps partly because of a bad overprint effect.

if printed without overprint effect you have only about handful of colours/tones you need to get about right, tone easily identifiable, and make sure you also get as sharp edges as possible with selected tones - you can select balance between sharpness and tones rightness. With overprint effect one needs to get also combinations look right, identifiable, so from line in dark green will not look dark enough to be mistaken as path or control ring as black road. And also keep objects sharp enough, also those overprint tone versions.

Overprint effect must be made really really well and carefully made and with a really good printer to make the map better than printing without overprint effect. With lesser printers may be impossible for tonal range of the printer not being good enough. Too often in green all objects ends up getting about the same darkish color with kind of blurry edges.


Here course printing and contour look pretty much the same to me on green:
http://www.ravinenkartor.se/show_map.php?user=Jaco...

as comparison, without overprint effect one can sure see the difference between control ring and contour, even in green:
http://stoltzen.no/okart/show_map.php?user=Sverre&...

Note how tones are made out of small dots of ink on paper, quite different from the representation on screen
http://ilm425.umb.no/~lanht/o/kartutv/printing/sam...

(note lack of sharpness and imagine what would happen if the gap between symbols of same colour is smaller than ISOM minimum)

@Jagge: I disagree with your assertion that it is better to skip overprint:

When done correctly it is definitely better to have overprint, particularly if you can increase the print scale! I.e. it is far easier to get good results in 1:10K or 1:7500 when the map was designed for 1:15K offset printing. :-)

As you note it is easier to get really sharp lines when you have a more limited set of colors, but even if the map itself is in "Normal" mode, i.e. not Spot, I really want people to use overprint for course printing!

It is so much work to do a good job cutting control circles and lines that it is almost never done, here it is (IMHO) better to get some bad color interactions from the overprint.

Re your samples from the web: The first one is probably an interaction between mediocre printing to start with and a less than state-of-the-art scanner!

I have often seen very interesting issues, not just moiree, when scanning badly printed (i.e. maybe 300 DPI or less dot raster printing) at 150-200 dpi, the on-screen result is barely readable.

Your second sample is indeed better but possibly not only due to overprinting issues but also scanner differences.

The final sample which must be Mr Tveite's reference set do show that printers are far from created equal. :-(

I have three HP 4700 printers, probably the big brother of the HP 4600 which is shown in that list: They produce useable output even for the 1:15K IOF test area, and very good results for 1:10K, using Spot colors for the base map and Draft Mode (i.e. overprint) for the course print.

In conclusion, we agree that it is way too easy to get map printing wrong, particularly if you are trying to work outside the design spec of the printer!

One particular problem with CMYK printing is the brown contours, which on my printer/paper combination require a mix of 4 spot colors to get it right. This is very hard to maintain for line widths of 0.14 mm (standard contour, 1:15K) or less: Even at 600 dpi you only get 3.3 dots across the line width, so to make the lines sharper the printer tries to locate most of the darker ink dots close to the edge of the lines.

Starting with photo resolutions (2400+ dpi) makes everything much easier, but also one to two orders of magnitude more expensive. :-(

here is a good example. There is not much contrast left between black and brown in green.

Would be cool test to print that also without overprint effect but with selected good colours providing sharp edges - with the same printer. And compare and figure was it worth doing to overprint effect thing, did it actually make the map more usable an how much.

Another thread reminded me that I did not complete my task - to make a simple statement about the overprint effect for those who know less than me. Here it is.

The current OCAD symbol/colour sets (what you get from File... New) use a technique called overprint. In skilled hands this is good. In unskilled hands it can produce undesired colour effects, such as ponds in open land turning out green. These days we expect that what we see on the screen is what we get on a printer, and these overprint effects are not thus.

If you are not familiar with overprint, I recommend you turn it off. Go into the colour table where there is a column for it, and untick all colours which are ticked.

One of the uses of overprint is to allow detail to show through purple course markings. You can do this another way by creating a special purple which is underneath eg black, Personally I find this not enough and I like to go over my course markings and make cuts over any detail.

The message: standard OCAD colour sets do not always print the way you expect. Results depend on how the file makes its way to the printer and you may be lucky. But unless you are skilled it is better to avoid "overprint".

It used to be that drafting and printing was hard, and only a few people were qualified to do it, and they took a lot of care because ordering a print run was a big expensive deal. Modern tools have made it easy for anyone to do, even if they have a very limited understanding of what they are doing. For example, I've known of several cases where courses were all 50% longer than the course setter thought (and advertised), due to confusion between 1:10000 and 1:15000, for example. I don't know of that ever happening in the "old days".

Heh...we have a few maps from the early days of OCAD where the OCAD file is at 1:15000, but the symbols are 1:10000 and you print it at 1:15000 and end up with a 1:10000 map. Confuses the hell out of setters.

@Juffy: That should be easy to fix.

There are two occurrences of "scale" in the menu items. "Extras–Change Scale" and "Options–Scales...".

Try changing the second one ("Options...") to 1:10000 and then printing.

Juffy will greatly appreciate the advice on using OCAD. He is so totally unskilled at the use of computers that he needs his dad to turn it on for him. Please forward further tips to him.

Giggle.

My day goes better when I can start the morning with a tRicky shot at Juffy, well a tRicky shot at anyone, really.
I am tempted to ask 'who is that guy?' but I get the feeling a dozen or so Aussies would shout back 'YOU DON'T WANT TO KNOW!'

Ask TrishTash - she's sure to give an unbiased answer :)

Gruver, there has been nothing magic nor difficult about producing overprint effect in PDF files from OCAD for some 6 years now. Take a look at my website info on the topic . It covers both OCAD and Condes output, PDF and even EPS.

When viewing a PDF file, if you can't detect overprint when you believe it should be there, then take a look at p14 of the guide http://ocad.com.au/wp-content/uploads/2012/04/Achi... The small print on that page covers an Adobe Reader setting that might need turned on.

And if your commercial printer prints but no overprint effect, then give them a copy of "A Digital Press Operator’s Guide to Process Orienteering Maps", also in that section on my site. The need for this guide is generally in franchise operations that might not employ true print professionals.

Regards, Ken

Thanks for that link. I knew most of it but not that I had to select "Press Quality". I wondered why I could never get the overprint effect from Condes printing to pdf; that was the piece I was missing.

Kenny, thanks for that guide. Can we put it on our club website?