Resolution and Document Dimensions

[Larb]

I don't get it. I've never really done much printing and I've not been using photoshop for long so I guess it may be one reason why it's not come up but here's my question:

In Photoshop when I go to make a new document I can set the document size in mm/inches or pixels. Then I can pick resolution.

Let's say I pick my image dimensions in mm, specifically 210mm x 297mm (the size of A4 paper, because I might be printing it out).

What effect does changing the resolution have on that?

[NeonKnight]

The resolution is how much 'detail' will be displayed per inch. So a resolution of lets say 72 DPI or DOTS PER INCH will half as much detail as a resolution of 140 DPI.

For a more indepth discussion of this check out this thread:

http://www.cartographersguild.com/showthread.php?t=2596

[Larb]

Ok, there is quite a lot there to read through, and I'm getting lost in some of the technical terms, so I guess one of my main queries was:

If I was to set the resolution from, 72dpi to twice that, or even ten times that, when I came to print the document out, would it still print out in the A4 dimensions I specified the document in?

[Redrobes]

Get number of inches -> 8x11, if you want a really high res print multiply by 300, 200 will be fine, or about 100 if you just want to look at it on the screen only. Then multiply and set your image pixel size to those and the res to the number chosen. I.e. 8x11 @200 dpi is 1600x2200 pixel image.

A bit pointless going much above 300 and you will find it limiting a bit much less than 100 or the notional 72dpi that they say the screen res.

The thread also says that you ought to make your map higher than these values and scale it back at the end but that's another story. I.e. go with 600dpi for working on the map until its finished then slightly blur it and resample back to 300dpi. If your not sure about that bit then skip it and do it at 200 or 300 to start with.

[RobA]

It is because ps is designed (originally) for print output. SO the paradigm starts with that.

I work on screen mostly, so I ignore page size and dpi and just work in pixels most of the time.

-Rob A>

[Midgardsormr]

Ok, there is quite a lot there to read through, and I'm getting lost in some of the technical terms, so I guess one of my main queries was:

If I was to set the resolution from, 72dpi to twice that, or even ten times that, when I came to print the document out, would it still print out in the A4 dimensions I specified the document in?

If the only thing you change is the print resolution (dpi, ppi, or pixels/inch), then the printed image will get smaller. If you also increase the pixel dimensions to compensate, which I believe PS does by default, then your image will still print the same size, but there will probably be noticeable artifacts from the resample.

[RobA]

which I believe PS does by default

Really? That is (IMOO) icky! No wonder people get confused

-Rob A>

[Redrobes]

Whoever was the first person to suggest that screen graphics are 72 dpi needs to be drawn and quartered.

Nobody suggested it. Get a 19inch monitor which is about 17.5 inches by 14 inches and set it to 1280x1024 screen res and you have 72dpi.

Small notebooks at about 17inch across but at the newer 1920x1440 res get up to about 115dpi but your spanky new 44 inch 720p HD TV is a mere 20dpi or so and then scraping the barrel is the projectors which are about 60in and 640pix which is about 10dpi - and they really look it too.