How do I set resolutions to get good results in print?

[smyrin]

When starting to make a map, it's important to decide on what DPI and what size you'll want to print your map. Because the size times the chosen DPI will be your minimum resolution. So let's say you want to print a map at a large size 12" by 18"... at 300 dpi printing that's a whopping 3600 by 5400 pixel file (in digital camera terms that would be a 19,44 megapixel image). That's why deciding your print size before making your map is important... because my computer will die a thousand painful deaths if I attempt something as big as that.

This is why I started this thread! I engaged a huge project on my PC cause I wanted to develop a world that I could have professionally printed. I read a few posts and it was suggested that I create the project at a 300 dpi resolution so that it would print well. So I started a Photoshop file at size 7200 x 7200 pixels and 300 dpi (24 square inches). My laptop can handle the file size and even the hundreds of layes (just takes 5 min to save it!). I thought I was setting this up correctly but after trying to test print it, I was confused about how the final was going to appear. I noticed that when I print on my home printer, I get a smaller version of what I was seeing on the screen and the quality was terrible. I test printed at Kinko's (pro) at 150% and 200% and they started looking good. This is all very confusing. I naturally assumed what I was seeing on the screen in PS7 was what I was going to get in output. This is not the case and I cannot figure out why there is a difference or what the quantative change is. I don't think it has anything to do with how I set up the file. The digital display of the image and the acutal print output just do not match in size ratio. I am beginning to think that the digital display is enlarging the image by 20-50% and the print output is in its correct size specified by the file.

[Meridius]

Hmm, I'll do a bit of math with my own monitor. As I do not know the physical dimensions of yours.

My monitor displays at 1280*1024 (it's almost square). For the sake of simplicity, I'll just take the width of the screen, since the height will (AND SHOULD!!) yield the same number anyway. It's 1280 pixels WIDE, and if I grab my tape-measure (which luckily also has inches on it, so I don't have to convert cm to inches), my screen is 'about' 15 inches wide. So 1280 pixels, divided by 15 inches, is 85,333... So the DPI of my screen is just over 85.

Let's do the math, your file is 7200 pixels by 7200 pixels. So on MY monitor your full res map would be just under 85 inches by 85 inches... (so I'd see only a small portion at a time of your map. Now, the more pixels per inch, the smaller your image gets. Because those 7200 pixels are a CONSTANT. If you raise the dpi, the physical size of the image in inches will be smaller. If you lower the dpi, the size will increase. But also remember that dpi also measures the amount of detail per inch.

I don't know how the 'quality' of your print ended up wrong, but this can have several causes:
1: Your colours are 'out of gamut'. Your monitor can show colours your printer cannot show. This only applies if the colours looked wrong.
2: Your printer is not fit for this job. This is unlikely, since I have a cheap multifunction printer myself, and it prints fine.
3: You have detail in your map which starts to look bad if it is compressed into a high DPI, this is quite likely, since you say that the large test-prints at the professional print-shop turned out 'reasonable'. 7200 pixels printed at 150 dpi is in fact the same result as printing your 300 dpi image 'on 200%'.

So, look up the current resolution of your monitor.
Grab a tape-measure, and physically MEASURE your monitor.
Divide the number of pixels by the number of inches. That is the dpi of your monitor. If you want your print at the exact same size. Print at that dpi, but be warned, paper doesn't tolerate 'low' dpi's as well as monitors do. Your monitors dpi is probably around 3 times as low as the dpi you're asking from your printer. Which also means the image on screen appears 3 times bigger than on paper.

I find that for gaming purposes, usually in rooms which have been lit 'satisfactory' and people just admiring the map from about 30-60 cm away (1-2 feet), 150 dpi is fine. 300 dpi is REALLY high quality, but I doubt people would see the difference without an actual side-by-side comparison.

Try to keep print and screen separate in your mind. If it helps, you can also activate the on-screen rulers in GIMP or Photoshop. This way you can get a good feel for the size of the PRINT.

[Midgardsormr]

First, printing a full color image at home on normal paper is very likely going to result in terrible quality. Ordinary copy paper will quickly be saturated by a 300 dpi print, and the ink will run, resulting in blurriness. Even high quality paper is unpredictable, and it takes some experimenting to develop a printing profile for a particular stock.

Now, as for the discrepancy between the screen size and the printout size, try the following steps:

Obtain the current horizontal screen resolution of your monitor. Under Windows, go to the Display Settings and look at "Resolution." The first number is the one you want.

Measure the physical width of your display—just the actual screen, not the frame. Divide the horizontal resolution by your screen's width. That is the actual ppi (pixels per inch) of your display.

Now, in Photoshop, go to Edit > Preferences > Units & Rulers and change the screen resolution to your actual ppi. The default is 72, which is almost certainly wrong.

Click once on the Zoom tool, and in the bar at the top, click the button that says "Print Size." Make sure your rulers are displayed (Ctrl-R if they're not), right-click a ruler and choose "inches."

Get out your physical ruler again and compare Photoshop's ruler to your own to be sure they're the same. If they are, then you know that whenever you are in this zoom mode—Print Size—the size of the print should be the same as what appears on your screen.

However, you may need to explicitly tell the printer driver not to scale the print, because that's just going to throw things off again.

I recommend that you do not work exclusively in the Print Size mode because you never know which pixels Photoshop is throwing away in order to show you that resized image. It's a good idea to reference the image frequently at both full resolution (Actual Pixels), and in Fit Screen mode, where you can see the entire image and know what it will look like from a distance.

Note that some of the buttons and menus may be a little bit different in PS7—I'm using CS4.

[Hai-Etlik]

Truly? I did not know that. In any case, though, I can't speak for every system (and not for Gimp at all, since I use PS), but I have seen no indication that my OS has ever known the physical dimensions of my screen. I currently have a very new full HD monitor connected via DVI, and although Windows has a lot of information about it, physical size does not seem to be one of those. Further, Photoshop has no apparent switch to enable it to take such data. You can, however, set the default screen resolution manually through Edit > Preferences > Units and Rulers.

Well I don't know about Windows, but X.org on Ubuntu has no problem with this. I can use xdpyinfo to bring up all the information about my display and dimensions and resolution are right there.

screen #0:
  dimensions:    1280x1024 pixels (339x271 millimeters)
  resolution:    96x96 dots per inch

It's a rather old monitor, it doesn't even have a DVI input.