To scale or not to scale

[Jaxilon]

Ok, I accidently did a whole map in 200dpi which bugs me because i was thinking about getting this printed for my gaming group.

If I scale it up to 300dpi does it just add in pixels and color them as it sees fit or am I better off just leaving it at 200dpi and learning the lesson?

I can't really see any difference when I scale it up but that's on my screen so I'm not sure what that would do to the printed copy.

I know we had some conversations about dpi a while back but I don't really remember anything about scaling up other than it not being such a good idea most of the time.

BTW - I'm using Gimp in case it matters (or in other words it's not vector).

[tilt]

well, as you say yourself, scaling up is always difficult. The more details in the map the bigger the chance of something getting messed up. So some pics/maps might scale nicely and some scale horribly
You can scale it up if you want to - what happens is that GIMP has to guess what color the extra pixels shall have, so if your map is 2000 pixels wide, and you want to scale to 300 dpi - GIMP will have to guess 1000 pixels pr row. A scaling trick can be to scale about 10% at a time - so you scale to 220 dpi, 245 dpi, 270 dpi, 300 dpi - this makes the calculation smaller each time and thus a little easier. Then you go through the map and see if its still crisp and fine - perhaps edit a little and thats it. What you should look out for is blurry areas

Photoshop has an option on how to recalculate when you resize and for enlargments you'll use "Bicubic Smoother", I don't know if there is a setting like that in GIMP.

[Ascension]

As far as I know increasing the scale reduces size. There are a total number of pixels across, right, 2000. At 200 ppi that's about 10 inches. Change that to 300 and it goes to under 7 inches. They take the existing pixels and not "make up" new ones...they just cram more pixels into an inch when printing. If you want to increase size then it blows the map up to the size you want, takes the existing pixels and doubles them (or triples them or whatever) in size and then uses the resampling methods to cut those bigger pixel blobs up into regular pixels. That's how PS does things.

[Gidde]

200 ppi won't print *that* badly. I've stretched a map as far as 150, and the pixelation doesn't register on my eye until I have my nose about 6 inches away from it. That said, I did size future ones so that they'd print at 300.

[tilt]

I do think jax ment the latter - scale = increased size - but sometimes one just read the wrong thing into a sentece so good thing you're double checking
and yes, if you change the dpi with the "resample image" off then the pixel size won't change but the "physical" size will - and as thus the image will print in the new - and perhaps improved - size.