Help with scaling an image down

[zbeving]

Hi all,

I've been cruising the forums for a few days now looking for how to scale a large image down to a smaller size and I can't seem to find a way to do it. Here's the specific problem I'm having:

I have an image that's poster size (34" x 24" ish) (6250 px x 5000 something px) I don't have the exact dimensions but it's quite large. When I go to print the map, the scale says that it is 1" = 5 feet (it is a grid battlemap) however the squares, when printed, are measuring 2" (way to large for a D&D mini). So I figured I need to half the size to get the printed grid to be an actual 1" square and wow was I wrong. Maybe I mathed wrong, but I ended up with 1/2" squares. I tried various pixel dimensions and couldn't find the magic 1" square. I assume I'm doing something wrong or overthinking a really simple fix that I just haven't seen or read about yet.

I figure there's an equation out there I don't know about (similar to how to scale up an image to print at 1" squares) and this is the place to ask. I'm using GIMP and printing in Excel so maybe it's the importing into Excel that's the problem.

Any help would be greatly appreciated. Thanks!

Zach

[Midgardsormr]

My guess is that you're printing with Excel to get the automatic page slicing? Try Posterazor instead. I think you'll get more predictable results. http://posterazor.sourceforge.net/

I think what you need to adjust is not the pixel dimensions of the map but simply the print resolution. I know your numbers are a little bit approximate, so what I give you here might not be the magic number. 6250 pixels / 34 inches gives 183 dpi (dots per inch). If the squares are coming out too large, I suspect you're printing at a lower dpi. I have no idea what Excel does with print resolution, though, so I can't help you set that up.

[johnvanvliet]

6250 px x 5000
a bit of a medium small image
should fit easily on a normal 8.5 x 11 inch paper

WHY ???
are you truing to use MS office spread sheet program "excel to print a photograph


just set the images pixels per inch setting in your printer settings software ( what ever that is HP,cannon,brother, ??? )
or in whatever PHOTO software this is ( if "MS paint" install photoshop or gimp )
the size ( 6250 px x 5000) has ZERO MEANING to printing
it is meaningless

the "dots per inch" or "pixels per inch " are how you adjust the size of the printed ( on paper) image

[zbeving]

For reference I'm following this tutorial for the printing portion: http://newbiedm.com/2009/01/13/newbi...-to-a-1-scale/ and attempting to apply the same methodology except to scale down the image not up.

So here's what's happening: If I put the image into Excel (insert -> picture) and format the page for Landscape printing and I make no other changes the image is so large that it will be about 30 some odd pages of printing. So my thought is if I adjust the scale in GIMP I can lower the size of the image so that it prints at the 1” grid square instead of the 2” grid square.

The tutorial is fantastic and works perfect for an image that has a grid square that is less than 1". What I can't figure out is the situation I have where the grid square is measuring 200px x 200 px using the measure tool. I'm guessing at this point there's a difference between the Image Scaling setting of px resolution (100 see below) and using the measuring tool where I get 200px.

The Image scaling box in GIMP looks something like this for the image:

Image size
Width: 6250 px (when switched to inches it’s about 34…)
Height: 5320 px (I don’t the exact number; sorry I’m doing this at work from memory)

X Resolution: 100.000
Y Resolution: 100.000

So how would I go about adjusting the px in the measuring tool? Or is it as Midgardsormr says I just need to adjust the dpi and if so how do I do that? Is it a print setting within GIMP or Posterazor? I’m not going to lie I haven’t messed around with GIMP much or Posterazor at all so please pardon my ignorance.

In the end I want the image to be larger than one sheet of paper because I'm putting it onto poster board for our games, but 30 pages is way to large (I don't want to have to use four poster boards just to create the map). If I could get it to print the exact size of a poster board that’d be fantastic.

In the end I found a work around by using a PDF version of the image and printing it in poster format at 50% size and it ended up being 9 pages and the grid squares are exactly one inch. I just imagine there would be a way to size the picture in GIMP so when printing it's not the 30 pages stated above.

Thanks.

[johnvanvliet]

i am guessing that you NEVER bothered to set the DEFAULT DPI on your printer
nor set the default dpi in gimp , if not set the printer will grab the monitor default( if a CRT then 72 dpi )

Width: 6250 px (when switched to inches it’s about 34…)

this tells me that you never set the printers DPI
and it is using about 150 DPI a very low setting ( ink saving setting )

just set the DPI in the tool provided by whatever brand printer this is

or
if using gimp
SET!!!! the DPI for the printer

[Midgardsormr]

Setting the dpi in the printer driver won't help with getting the correct scaling, nor will it affect anything in the Gimp dialog box. In fact, it's a good idea to put it into draft mode for a test print first to make sure you don't waste a ton of ink on a print that's at the wrong scale. The draft mode in the printer driver will downsample the image prior to printing, essentially reducing its pixel dimensions at the same time as it decreases the dpi. It won't change the scaling unless you tick a box that says something like "fit to page."

Anyway, there's a mismatch somewhere in there. The X and Y Resolution in the window you describe is the dpi, but with the numbers you give your image should be 62.5 inches wide (6250 pixels / 100 px / inch). I'd say the simplest way to get to where you need to be is to count the actual grid squares across, then adjust the resolution until the width in inches is equal to the number of grid squares. Then you'll be certain that one square = one inch.

Don't let it resample anything—you don't want to go throwing away pixels.

My inclination is that you should download Posterazor and let that do your tiling. I have a feeling that putting Excel into the mix might be adding additional needless complexity. It's not really designed for this kind of thing, so it's unlikely that it does it as well as a program dedicated to exactly this job would do.