What resolution do you design at?

[Gamerprinter]

Also, while Max states that 150 dpi is good enough for posters - that depends. Things like small fonts as labels, especially in point sizes smaller than 10 point, cannot be read when printed unless at least 300 ppi. When you see a poster that is any higher resolution than 300 ppi, the primary reason is very small text is included in the design. An 8 point font size, cannot be read at 150 ppi. A purely raster image such as a photo with no text, prints fine at 150 ppi, depending on the level of detail in the image.

[feanaaro]

Does not the dpi mean something only when you are printing? On your monitor you only see pixels anyway, if you have a 3000px*2000px image, you will see it all the same way (both in photoshop/gimp and when exported as a jpg/png on the web) regardless of the dpi setting. If you have enough pixels, you then can change the dpi for printing at any point. Isn't that right?

[rgcalsaverini]

@Jalyha: You seem a bit lost about resolution, it roughly works like this:


What is DPI
Printers and screens alike work with discrete units to represent images (unlike our eyes that see things as a continuum), so the density of those units can make a huge difference on how the image is perceived. DPI (Dots Per Inch), its a measure of how many colored dots (minimal graphic unit, on screens they are called pixels) can be placed in a line of one inch. Theoretically DPI is used only for physical things, and on screens you use PPI (pixels per inch), but since they are more-or-less analogous you can use DPI for screens too.

If I'm only using them on the forum, what PPI/DPI do I need for my images? 72, right?
No, provided you work with pixels (not inches, cm...) actually it doesn't matter. You see, your screen have a fixed* resolution setting, if that is 72 PPI, that means that every single image that you see on your computer will be displayed with 72 PPI. Try it yourself, create an image on GIMP with 10000 DPI and another with 2, same size, and draw on both. Any difference?
It will only be important once you print your image, the printer on the other hand display things with the resolution it is told to.

Does DPI settings affect the size that my image takes up on disk?
Working with pixels? Nope, again, this resolution information is not used by the computer. If you create an image with 500x500 pixels, it will take the space that 250000 pixels would take regardless of the resolution you are creating it with.

When DPI/PPI matters?
When you are using inches** instead of pixels, and when you intend to print. If you intend to print an image with 5" x 5" with 72 PPI that means that you have 72 dots per inch in a line, so your image will have 360x360 pixels. For 300 PPI, the same image would have 1500x1500 pixels.

How much DPI/PPI for printing then?
It depends of a series of factors, between the most important is the distance that your viewer will be looking at the print. A billboard is print at a pathetically low DPI setting, because people will be looking at it from far enough so the details wont be relevant. A good rule of thumb for book-distance is ~300 DPI, poster distance ~200 DPI (deppends on poster viewing distance). Note that the smaller the thing, the closer people will look at it.

Bottom line: For anything but scanning or printing, ignore the DPI or PPI setting and use pixels.

* You can change resolution on settings, but that is fixed once set, so...
** I don't know how much an inch measure in real, usable units, so I'm sorry if my examples make little sense numerically

Edit: Fun-fact: The "72 is the default for computers/internet" is an outdated thing that holds no meaning anymore, and this myth is propagated by the default setting of cameras and image manipulation software. PPI is a screen setting, not an image setting. As said before, it actually makes no sense to speak of a default image resolution for screen. Pixels are context-bound..

Around 1770, François-Ambroise Didot used slightly larger ciceros to fit the standard French “foot.” Didot’s pica was 0.1776 inches long and divided evenly into 12 increments. Today we call them points.
In 1886, the American Point System established a “pica” as being 0.166 inches. Six of these are 0.996 inches.
None of the units ever strayed far from 12 points per pica: 6 picas per inch = 72 points per inch. It was an important standard by 1984, when Apple prepared to introduce the first Macintosh computer. The Mac’s interface was designed to help people relate the computer to the physical world. Software engineers used the metaphor of a desk to describe the arcane workings of a computer, right down to “paper,” “folder” and “trash” icons.
Each pixel on the original Mac’s 9-inch (diagonal) and 512 x 342 pixel screen measured exactly 1 x 1 point. Hold a ruler to the glass, and you’d see that 72 pixels would actually fill 1 inch. This way, if you printed an image or piece of text and held it next to the screen, both the image and hard copy would be the same size.
But early digital pictures were clunky and jagged. As screen technology and memory improved, computers were able to display more pixels on the same size monitor. Matching a print-out to the screen became even less certain when raster and vector apps allowed users to zoom in and examine pixels closely. By the mid-1990s, Microsoft Windows could switch between 72 and 96 pixels per inch on screen. This made smaller font sizes more legible because more pixels were available per point size.

[Azélor]

yea I think DPI is irrelevant when you are not printing. More DPI is the same size in real life. The files will have more pixels so it will appear bigger on screen. It's same size but have more details. To make a comparison: 72 DIP is when you are using a large paintbrush and 300 DPI is with a fine pencil. The latter can have more details.

[Jalyha]

Everyone is being so helpful But I'm not real bright So..

Right now I have a 4000 x 3000 image (or is that reversed?). The setting for the file on GIMP is at 72 *PPI*.

I can't figure out the "export" thing, so I've been doing the "Select all" - > "Copy visible" thing, pasting it into paint, and saving as a .jpg.

But it worked until I went from 3000 x 3000 to 4000 x 3000. Then, I tried to upload that picture, and it said it was too big (6 point something mb where we can only do 4 point something...)

So I resized the image to about 85% (I tried more, but it didn't work till 85) and the forums accepted it, but the picture looked AWFUL.

If I open a new image and set it to, say, 300 PPI, and copied everything over to that image, would that A) Change the file size? and B) Make the picture look better if I *do* have to resize it?

Or... I don't know. How to make my picture pretty again? ;_;

What I'm trying to figure out is how to post the picture the way it's saved on GIMP

[Gamerprinter]

Yes, in my last post, I used 150 dpi as regards to a poster - posters are a printed media. However, when I post images here, they are measured in ppi since it only shows on the screen. Also 72 dpi was the standard screen resolution, 10 years ago, most computer monitors use 96 ppi today. When I create a map at 100 ppi, the intention is that it will probably never be printed, instead used in a VT app.

[- Max -]

Also, while Max states that 150 dpi is good enough for posters - that depends. Things like small fonts as labels, especially in point sizes smaller than 10 point, cannot be read when printed unless at least 300 ppi. When you see a poster that is any higher resolution than 300 ppi, the primary reason is very small text is included in the design. An 8 point font size, cannot be read at 150 ppi. A purely raster image such as a photo with no text, prints fine at 150 ppi, depending on the level of detail in the image.

Some poster maps hanged on my wall don't say the same

[Gamerprinter]

Because I run a digital print studio and serving RPG gamers is a major source clients, you shouldn't be surprised that I have large format printed maps all over my shop - I can think of 2 dozen prints scattered around my shop and that's just the large format (poster size) ones. I have half a hundred letter size and tabloid size maps in nooks and crannies throughout my shop. All were printed 300 dpi or higher resolution.

[- Max -]

Looks like a nice shop I use to work with several print shops that requires 150 dpi for large posters maps and provide excellent quality maps. Those professionnal printers clearly tells me that for poster sizes, resolution upper than 150-175 is superfluous and I can see it on thr maps they printed for me, even if my walls are probably smaller than the ones in your shop

[Jacktannery]

Everyone is being so helpful But I'm not real bright So..

Right now I have a 4000 x 3000 image (or is that reversed?). The setting for the file on GIMP is at 72 *PPI*.

I can't figure out the "export" thing, so I've been doing the "Select all" - > "Copy visible" thing, pasting it into paint, and saving as a .jpg.

But it worked until I went from 3000 x 3000 to 4000 x 3000. Then, I tried to upload that picture, and it said it was too big (6 point something mb where we can only do 4 point something...)

So I resized the image to about 85% (I tried more, but it didn't work till 85) and the forums accepted it, but the picture looked AWFUL.

If I open a new image and set it to, say, 300 PPI, and copied everything over to that image, would that A) Change the file size? and B) Make the picture look better if I *do* have to resize it?

Or... I don't know. How to make my picture pretty again? ;_;

What I'm trying to figure out is how to post the picture the way it's saved on GIMP

Jalyha, yeah its a bit confusing but I will try to help. The posters above explained much better than I can but here goes:

1. Recently I was asked in EN World forums to help a fellow DM resize an encounter map for printing. He had an encounter map from a module that he wanted to print out so that each grid square measured one inch. To help him I did the following: I took the encounter map .jpg and opened it up in GIMP. I checked its resolution: it was at 72ppi, which is standard. Then I measured the size in pixels of one grid square. It measured 39 pixels across. So in GIMP I went to 'IMAGE > SCALE IMAGE' and changed the resolution to 39. This made NO CHANGE to the image at all; all it does is tell the image that 39 pixels should look like one inch. I then saved the image (it was exactly the same size in terms of memory) and posted it to the fellow DM. He was delighted! Now, when he imported the image into WORD it filled up the entire page, instead of only half the page, and he knew it would print out at exactly the right scale. This is all PPI/DPI is.

2. To upload your images to the forums you don't need to worry about ddi. What you need to worry about is COMPRESSION. When you have an image of size 4000x3000 pixels and you export it as a .PNG or similar losless format it will measure c. 20mb, which is huge. You could reduce the size of your image in advance by 50% to say 2000x1500 pixels and then export it to make it smaller, but you would lose a lot of detail. So what you do is you export it in a LOSSY format - JPG is a very good one to use. Open that same 4000x3000 and this time export is as a .jpg. A dialogue will pop up offering a quality slider - I always leave it at default, usually 85-90%. This will export your image to a size of about 2-3mb, which is the right size of these forums. If you compare the 20mb exported PNG with the 2mb exported JPG I guarantee you will notice little or no difference in image quality. There is a significant difference obviously, but not one you need to worry about for this purpose - just make sure you keep the original GIMP file and only use the GIMP file to make changes to your document. The .jpg should just be used to post.

Hope that helps.