Having spent nearly a year and a half scanning pictures and creating plans perfectly scaled to size, I've decided to explain the whole process including all of the complicated mathematics so that you can do your own plans instead of waiting for me to get round to it !!!
As the vast majority of plans are in 4mm, then we need to shrink these in a photocopier to get the size we want, exceeding copyright along the way and it has recently come to light that one railway modelling magazine has been turning out incorrect plans for a long time, so you would just be re-sizing the errors ....... I'm not saying which one, but if you don't model BR Modern Image, then you're safe !!
Another way is to scan and resize in Paintbrush, adding detail along the way and scaled to print out a perfectly sized plan - it sorts out the copyright (as the original is used only as a guide) and extra detail can be loaded in at the time.
Although very deeply hidden inside the settings of Paintbrush, the program prints 1mm for every 3.79 pixels - why not open Paintbrush and draw a line 379 pixels long ... this prints a line 100mm long (and if it doesn't, check your printer driver is the right one !!)
Now if we equate this to 3mm/foot scale, each foot of scale model equals:
3 (scale of 3mm/foot) x 3.79 (pixels to print a mm) = 11.37 pixels
If you want to print a scale foot of model, do 11.37 pixels (or 11 pixels gives you 11.60 scale inches ..... wow !)
I don't need to tell you that each pixel equates to about a scale inch, and the variance in size is about +/- 4%, so not a great deal and the accuracy isn't really grim (especially since you didn't pay extra for the program) !!!
Now we know how big the image should be when we've scanned it !
Now this is a real problem with scanners - I haven't found one yet, that will scan an image and print it exactly the same size, so we have to 'calibrate' our scanner
Take one clear plastic ruler (15cm ones are a nice size !), scan it as a bitmap, open Paintbrush and print out the scanned image - now measure from the zero mark of the image to the 10cm mark ..... bet it's not 10cm !!
It's wise to measure a decent length to improve any rounding errors.
Say (using my office scanner as an example) you measure 15.8cm for that 10cm of image - that will give us a Correction Factor of:
158 (actual mm of measured distance) / 100 (mm of measured distance) = 1.58
Keep hold of this Correction factor - this will guide you closely in the scans to come.
This is it - this is the moment that will make or break your scanning and mathematical abilities.
Take your plan and scan it, convert as BMP and open it in Paintbrush - looks a bit chunky, and almost sure not to be the right size, so it's correcting time !!
Let's take the example of using a 4mm plan in the office scanner, and wanting a nice 3mm example when printed - here's the calculation:
3 (desired scale in mm) x 3.79 (pixels per mm) / 4 (scale of original) / 1.58 (correction factor) x 100 (percent) = 179 (percentage correction with no decimal places)
Now I know that looks daunting, but if you do loads of 4mm plans down to 3mm using the same scanner, then you calculate this once - Windows does have a Calculator, after all !!
Now go to Paintbrush and select 'Image' and 'Stretch/Skew' from the tool bar, and feed this magic number into Horizontal Stretch and Vertical Stretch (seperate operations in 3.11 and 95 - combined in NT4.0 and 98 - don't know about 2000 and Me yet !) and your image will resize .... do a Save As and change the file name to something else (so if you've got it wrong, you don't have to re-scan again !!)
Now do a final check using our original calculation in Sizing up your image - if you've got it right, then the scale feet will be fairly close to the pixel count and you're all ready for the clean-up operation to follow.
But that's a topic for next month !!
Return to: Archive Articles Index