DPI vs. PPI - What's the difference?

[Gamerprinter]

The issue with my exterior map is that I scaled it at 1" = 20 feet and it measures 54" x 43", thus the true measure is 1080 feet x 860 feet.

Even if I forget about DPI and stick with pixels only. At 200 pixels every 5 feet, that's 43,200 pixels wide by 34,400 pixels - Xara won't let me export something at that size. In fact Photoshop won't let me create or open an image that is larger than 30,000 x 30,000 pixels.

This means I need to slice my image into multiple pieces, probably in quarters.

I was able to force the dpi down to 50 in Photoshop, but it would still not let me create more than 30,000 pixels in any dimension.

Lastly Kalmarjan describes a maximum normal map size at no large than 100 x 100 feet at 4000 x 4000 pixels. My map is almost 10 times that in dimension. It might be best for me to cut this image into 10 separate maps.

Thoughts?

[RPMiller]

You must be using an older version of PS. CS3 doesn't have that size restriction.

Breaking it up into smaller pieces would certainly work, but it would be a little clumsy.

Regional maps in VTTs are not that small. In fact, one of the strengths of MapTool is that it practically has no maximum size. Realistically it does, but it depends on what is on it. That also is assuming that you are creating the map directly in MapTool instead of importing an external pic. Some of the tests we've done have been with maps that were a mile long and longer per side. As I suggested before, you should sign up at the various VTT forums and take a look at their capabilities and what others are doing if you are serious about getting into that market.

[Gamerprinter]

So I should download the newest version of GIMP, since I don't plan to upgrading PS anytime soon. The latest GIMP should be like the newer versions of PS in this respect.

Yeah, I'm using PS 5.5, quite old. I got disgusted with some of the features to CS and never upgraded because of them.

Still Xara won't export the full map at that pixel resolution. Xara still looks at it in DPI and says it is limited by 9 feet in any direction (!)

[Gamerprinter]

Knowing that I have an older version of PS with a limitation of 30,000 pixels in every dimension, first I cropped the original exterior map to just the compound the octogonal walls and everything within and a few outside trees.

I opened and rescaled the map in PS without resampling and ended up with a map file at 200 pixels = 5 feet. Conversely, the non-essential DPI data is 7.25 dots per inch. Still the file is 25.5 MB in size and in PNG format.

I feel this is still too large, however, I can upload into my FTP account if anyone (RP specifically) wants to download it for their own uses.

Once I get an upgraded version of GIMP I'll probably be able to do the entire map, of course the file size would still get much larger.

Thoughts?

[Robbie]

Wow...see, for stuff liek this I think targetting VTT with maps of this scale woudl require some forethought...and I'm not slighting your process at all, becuse this all came up after your map was 80% or so done...but forethought would need to be in place to map the subject in sections...

Again though, this takes me back to thinking about the google maps api and how they handle the growing scale of the street level map...I imagine they are definitely usign a vector tool to create the street maps...but they're rendered in various different scales for the tile server...Each tile is 256x256 and the google api does all the work of placing the tiles in order and together...its pretty impressive, and I think a slicing tool would be perfect for that if a VTT took advantage of a tile server for maps...something to think about at least...

In other news...I'm so very glad to see that this conversation is staying professional and mature. There's obviously going to be differing opinions, and there's nothign wrong with being headstrong about being corrected, but the fact that this stayed mature makes me very happy...kudos and rep to all.

[Gamerprinter]

Xara Xtreme has a very effective slicing tool within, so creating multiple pieces of a specific size is no real problem.

One descrepancy I've found, however, is that "shadows" are attached alogrythymically different than other objects. When I slice an area that includes a shadow, but not its "casting object", it doesn't slice off. I am forced to redraw a polyline copy filled black and given an equal amount of transparency to look like the shadow. This could be quite disconcerting around many or complex shadowing in a sliced area.

Of course I can always export it as a graphic image, then import it back in to slice it up. But the graphic version is not editable as it would be in Xara (.xar) format.

So the other descrepancy on export size limitations is almost mute, in that I can (in most cases) slice the map to optimal sizes for VTT easily.

[Kepli]

Many thanks for the explanation and especially the link RPMiller. I knew almost all of this already, but it is tough to explain to others. Now I can just point them to the link and let them read the complete story

[RPMiller]

My pleasure Kepli! It was a real stickler for me for some time as well so I can't really fault those that are going by age old assumptions. Now that the information is out there is no excuse for ignorance any longer. Hopefully folks will look into it more and it will finally start to click for them like it did for me.

P.S. You have a typo at the end of your sig. Fortunately no one reads them, otherwise they would have pointed mine out a long time ago.

[Midgardsormr]

Gamerprinter, I'm working on a map that is ultimately going to be printed at poster size, around 20" X 30". I'm not sure what equipment the print shop will be using, but I was concerned about what dpi I should aim at. My understanding is that 200 - 300 is the recommended target, but I wanted to be sure, so I looked up the guidelines on your web site, where you recommend 72 dpi to users of Photoshop, et al.

So will 72 dpi provide sufficient quality for a good-looking poster sized print? I started at 300, so I can rescale easily enough.

[Gamerprinter]

72 dpi works as long as the map file created was made at your correct dimension and scaled at 72 dpi when you export the file.

If you convert a higher or lower resolution file to 72 dpi or rescale your map to 20 x 30 when it wasn't that in the first place - then 72 dpi is not what you want - it will look crappy.

Using high resolution like 300 dpi is required if your map file has to be rescaled to fit the dimensions and resolution you ask.

In other words, if you don't have to rescale 72 dpi is fine, if you do have to rescale start with a higher resolution...

I hope that wasn't too complicated?