05 Northrop F-5


05 Northrop F-5

This is a real world example. This F-5 plan was found online here - http://www.jpaeromodels.com/planosvuelocircular/Coleccion%20Modelhob.htm - on Dec 17 2011. It is in the form of 2 TIFF files that are very large in filesize.

Page1 : 3,196KB
Page2 : 3,399KB


We want to take these 2 TIFFs and make out of them 1 (paged) PDF plan that is clear and accurate, and prints out at full size. We want the filesize to be under 800KB.


In this tutorial I am using Photoshop CS3.

1. Start by dragging Page1 TIFF into Photoshop, and having a look around. Check we are in Greyscale mode. It then needs cropping for a start.


2. If we crop the plan to tidy up the edges, then do: Image/ImageSize to check the properties, can see the image is correct width and height at full size, and the resolution is 300dpi. Which is exactly what we want. So our work here is done. Hurrah:


3. But no. If we go on to our usual save as PDF, the filesize comes out as 3,653KB - and that's just for the first half of the plan. That's no good to us, we are aming at about 10% of that. Why is the filesize so large?

Ok let's zoom right in (200%) and take a look. It looks like it has been scanned and posterized into a 2 colour bitmap, but done so that it includes a lot of surface noise. Or maybe thats just the way the scanner output comes. Either way, it is that level of "bittiness" that is causing such a large filesize. The PDF that we create will be carefully copying and recreating all that surface noise.


4. Let's try re-sampling downwards. Check you are in greyscale mode. Change the dpi down from 300 to 200.


5. Ok. That's kind of squished the pixels together and smooothed things out a bit. Now adjust the contrast up to get more clarity again:


6. We don't want to go too far, because we are losing some detail along with the noise. But lets repeat those steps and go down to 180 from 200 dpi, that might make it look even smoother:


7. OK. Now, let's go back up to our target 300dpi, and carry on as normal:


8. Now do our usual Posterize to 2 levels, and now have a good clear plan. We haven't lost any important detail. Compare this view with the pic in step#3:


9. Zoom out and have a look around. Looking good. Now we are back on track and just need to continue as always with final processing and export to PDF:


10. The final steps are exactly as in steps 16-20 of Tutorial 02 so just to quickly recap: Bitmap at 50% threshold with 300dpi, Save as PDF with the usual settings. Then of course we do all that again with page2 of the plan, then use Pdfsam to append the 2 files into 1 PDF as shown in Tutorial 03.

That's about it. The finished file came out (both pages) at 795KB. My copy is here www.outerzone.co.uk/plan_details.asp?ID=2049 if you want to have a look.


The reason I go up to 300 dpi again in step#7 rather than just staying at a lower dpi is that posterizing seems to work less well at lower dpi. But that it just the way I see it. Your mileage may vary.


Hope that all made sense. You can email feedback to: steveWMD@outerzone.co.uk