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

[tilt]

its raining cats and dogs and 6 degrees celcius - so typical spring *lol* ... and I'm actually danish living i sweden so I concider myself an Öresund citizen

[Carnifex]

It's raining. Surprised?

Well to the subject again:
Go to Image > Image size...
If the resolution is set to 300 dpi you can easily see the document size right in that window (just above "Resolution"). Of course the actual printing size can be changed if you use the image in another program (like Adobe InDesign).

(about what Tilt said but explained in another way)

[tilt]

you can never explain this in enough ways, its a dfficult subject for most ... until of course they get it.. then its... "ah.. NOW I see, thats easy "

[Hai-Etlik]

you can never explain this in enough ways, its a dfficult subject for most ... until of course they get it.. then its... "ah.. NOW I see, thats easy "

Yep, the problem is most people just can't wrap their heads around how simple it is, they try to find some complexity that isn't there and get confused when they can't find it.

I think what might be the problem in this case is that even though there's a bit of metadata that says "display at 300dpi", when it's displayed on the screen, that is being ignored and it is being displayed at the native resolution of the screen.

In The GIMP, open the View menu and turn off "Dot for Dot". This will make the GIMP resample the image on the fly so it will appear at the right size. There should be a similar option in other raster image editing software. (This won't touch the underlying image data, it just changes how it's displayed)

[Midgardsormr]

It also doesn't help that we continue to hear phrases like "The resolution of the Internet is 72." That is a direct quote from a web design teacher at my university; I almost threw something at him. Then I calculated the total number of public addresses in IPv4 and divided it by the land area of the planet to learn that the actual resolution of the Internet is about 26. Of course, that's going to be thrown off somewhat by satellites and ocean-based nodes, so I have no idea how close the number actually is.

Incidentally, the printed size of the image will still likely be different because Gimp doesn't know how large your screen is. It will probably assume 72 ppi, but that is only going to be correct a fraction of the time. My screen, for instance, is 19" wide and displaying full HD (1920 horizontal pixels), so it's a little more than 101 ppi, which means that when I hit the "Actual size" button in Photoshop (yet another misnomer) the image I see is quite a bit smaller than it would print. My HDTV, on the other hand, is 23.5" wide but only 720p (1280 horizontal pixels*), so its resolution is a mere 54 ppi.

Since we're offering additional new explanations, I thought I'd point out the "word math" involved here. "Per" means division, so "Dots per inch" is equivalent to dots (pixels) divided by inches. dpi = pixel / inches. Now you can use algebra to rearrange the equation to solve for whichever piece you're missing.

Want to know the resolution you need to print a 2000 x 3000 image in an area of 8" x 10.5"? dpi[w] = 2000 / 8 = 250 and dpi[h] = 3000 / 10.5 = 286
In order to fit the image in the vertical direction, you need 286 dpi. You have to use the bigger of the two numbers to avoid the image being cropped on the other sides.

Need to know how to set up your document to print at 300 dpi in an area of 10.5" x 16.5"? 300 = pixels / 10.5 and 300 = pixels / 16.5. Rearrange to pixels = 300 * 10.5 = 3150 and pixels = 300 * 16.5 = 4950.
The pixel dimensions of your document need to be 3150 x 4950.

How big a piece of paper do you need to print your 6000 x 4000 image at 200 dpi? 200 = 6000 / inches and 200 = 4000 / inches. Rearrange to inches = 6000 / 200 = 30 and inches = 4000 / 200 = 20.
You will have a poster print at 30" x 20".

dpi = dots / inches


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*That's not really accurate, since my TV doesn't use square pixels, but that's a completely different topic that I won't go into here. It's close enough for government work.

[Hai-Etlik]

Incidentally, the printed size of the image will still likely be different because Gimp doesn't know how large your screen is.

Yes it does actually, at least if the OS/Windowing system knows and reports it accurately.

[Jaxilon]

Asking it another way - As long as my dpi on my Gimp image is different than the dpi on my printer then it will print a different size?

Personally, I have my dpi in Gimp at 300 but my printer can do 300dpi or 600dpi - I'm going to go experiment with this now. I wanted to print something at 3" x 5" but it came out about 75% smaller...I'm thinking because I was 300dpi and 600dpi.

Bah - changing my printer to 300dpi doesn't seem to have changed anything. When I look at my "image properties" it shows 100 x 100 ppi <--- I know it means pixels per inch but I don't know if that is the same as dots. I guess Pixels is screen and dots is printer...so if I create my image at 600ppi would that print out correctly on my laser at 600dpi? I've almost given up on getting a 3x5 printout because I can't seem to get this.

What's killing me really is that I attempted to create a create a new template in Gimp for a 5x3 inch card but I seem to have failed utterly to have set it up right. I don't really care what it looks like on the screen but I need it to print at 5x3 inches.

[Meridius]

dpi = dots per inch

How big is your file in pixels?
Divide the number of pixels by the number of inches you want the print to be. That will be the DPI at which you'll have to print. DPI on computer screens is an 'empty' word.

Let's say your file is 1500 by 2500 pixels. 1500 pixels divided by 3 inches = 500 dots (pixels) per inch. 2500 pixels divided by 5 inches = also 500 dots (pixels) per inch.

Let's say you want a 300 dpi print in 3" by 5". That's 3 inches times 300 dots (pixels) per inch = 900 pixels. Also 5 inches times 300 dots (pixels) = 1500 pixels. So if you want to print at that size at 300 dpi, your file needs to be AT LEAST 900 by 1500 pixels.

It's just that stupid programs like GIMP and Photoshop decide how big an inch is on your screen, which probably isn't true to reality.

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. I wanted a map of about that size (glue and a poster-print setting can make A4's into A2's real easy), but decided to go with 150 dpi, it's more than sharp enough. People won't be going over it with a spotlight and magnifying glass, so you can easily get away with 150 dpi. 12" by 18" at 150 dpi gives a much more 'managable' 1800 by 2700 pixel image (only 4,86 megapixels). Now I went slightly over my design specs, and ended up with 2000 by 3000 pixel file (and my computer still had a hard time, but at least it hasn't blown up in a spectacular fireball).

[Jaxilon]

dpi = dots per inch
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. I wanted a map of about that size (glue and a poster-print setting can make A4's into A2's real easy), but decided to go with 150 dpi, it's more than sharp enough. People won't be going over it with a spotlight and magnifying glass, so you can easily get away with 150 dpi. 12" by 18" at 150 dpi gives a much more 'managable' 1800 by 2700 pixel image (only 4,86 megapixels). Now I went slightly over my design specs, and ended up with 2000 by 3000 pixel file (and my computer still had a hard time, but at least it hasn't blown up in a spectacular fireball).

This would be good to have in our FAQ or beginner's guide because I'm only now starting to get it but it's a question I came here with. I haven't tried to print any of my maps yet but I can foresee all sorts of headache if I tried with what I've made so far. I just ripped a number of pixels out of my head and started making a map. Now I can plan. I will see if I can get this stupid 3x5 card thing to work now using what you just explained. Thanks.

[Midgardsormr]

Yes it does actually, at least if the OS/Windowing system knows and reports it accurately.

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.