04 Little Herbie


04 Little Herbie

This is a real world example. This 'Little Herbie' plan was posted here - www.rcgroups.com/forums/showpost.php?p=20077754&postcount=101 - by perttime on Dec 07 2011. It is in the form of 3 separate scans in JPG format that will need stitching together. The scans are colour and they are blueprints.


This is a real world example, but I am cheating in 2 small ways. First, in reality perttime kindly did all the work for us and posted a cleaned up, inverted and stitched plan, so it seems slightly perverse to ignore that and do all the work again, but hey this is a tutorial and we need to show something. Second, this model has no known correct wingspan, so I'm just going to ignore (not do) scaling to a fixed wingspan.


We want to take these 3 JPGs and make out of them 1 PDF plan that is clear and accurate (with black ink on white paper), 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 all 3 JPGs into Photoshop, and having a look around. They are fairly low res, at 72dpi and a height of ~13". That's fine.


2. Ok. Let's get to work. We don't want colour - it just gets in the way and uses up filesize. So first of all let's do Image/Mode/Greyscale on all 3 images:


3. Zoom in one the first image. We want to check it is lined up to the horizontal. Drag a horizontal guide down from the ruler onto any datum on the drawing, the centreline seems a good place. It looks like we need to rotate the drawing ClockWise a little.

Select All. Do Edit/Transform/Rotate, and note the options widow information, showing a rotation of 0.0 degrees.


4. With that value highlighted, tap the 'up' arrow on your keyboard to adjust the rotation of the drawing by 0.1 degree at a time. Keep an eye on the centreline and your guide as you tap to get them to match up . I make it 2 taps, and now we are straight. Press the Enter key to apply.


5. Ok. Thats drawing 1 of 3 done. Now lets make this canvas bigger so we have room to stitch on the next 2 parts. Zoom out. Do Image/CanvasSize, and in this dialog box, set the Anchor as shown to the LH side/edge. Set the width to say 30" and set the height up a couple of inches to say 12". Apply.


6. Ok, so now we have some room to maneouvre. Now lets organise our workspace and get ready to drag and drop the other 2 drawings into that space:


7. Done. So now we have a single image file, but with 3 layers: background, layer1 and layer2.


8. Zoom in. Get focus on layer1 (by this I mean make it blue in the layers window, as shown. That's how you select which layer you're working on). Use the Move tool to drag layer1 into place vertically, so the centreline is on your guide. Check for alignment, and yes it looks like it needs a little CW rotation.


9. Same as we did in step 4, rotate this part of the drawing to horizontal alignment by doing Select/All then Edit/Transform/Rotate, highlighting the angle value, then tapping the up arrow key a few times.

OK. Now we can nudge layer1 leftwards into place, where it should match up nicely... oh no, rats. Scratch that. That looks all wrong now:


10. Looks like the problem is the two layers dont match up exactly in scale. Layer2 needs reducing a little. Ok. Zoom out. Use the 'Move' tool to drag layer 2 upwards a little so that its bottom LH corner is in the right place, and is lined up nicely with the Background layer. We will scale from that fixed point. That makes it easier to get things lined up than scaling from the centre. Do Edit/Transform/Scale. This displays (amongst other things) a bullseye symbol in the centre of the selection (ie in the centre of layer1). Find it and drag it downwards and left.


11. Drag the bullseye symbol to the bottom LH corner of layer 2 and let it snap to that point. Zoom out, check your options window and make sure you have the chain button clicked, to keep constant aspect ratio when scaling. Good. So. Now hold and drag the topLH corner to rescale layer 2 slowly smaller, until it matches with the background layer:


12. Looking good. Ok, so we have them both aligned to the horozontal, both at the same scale, both ligned up vertically against our datum (our guide from back in step 3)... now we just need to align them left/right against each other, and we're done.

Normally would be helped by the scans overlapping slightly to show us more detail, but here... there is no overlap. Ok, the best we can do is look for clues like things with constant repeated size, like say the pattern of the hinges on the tailplane. Spend a while nudging layer2 left and right until it looks about right.


13. Ok. So that's 2 down and 1 to go. Now we need to do exactly the same again (steps 8-12) with focus on layer2. This gives us a complete drawing to look at:


14. Looking good. Now Flatten layers, and Crop the edges:


15. Now to reverse the print colours. Do Image/Adjustments/Invert:


16. And then we are about there. Let's also change the image size to to 300 dpi (Resample) while we're here:


17. Ok. Scaled up to a 24" wide page now. I guess now would be a good time to scale the plan up to the correct exact wingspan, but like I said at the start, we're skipping that step in this tutorial. The issue of scaling up to full size is shown in both tuturial 02 and tuturial 03


18. Do Image/Adjustments/BrightnessContrast, and give it some welly.


19. You know the drill now, right? Next, we Posterize to 2 colours:

20. 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.


That's about it. The finished file came out at 131KB. My copy is here Little_Herbie.pdf if you want to have a look.


It has occurred to me that the sequence I do this in may not be optimal. I don't have any training in this, I'm just making it up as I go along. I wonder if resampling should be done at an earlier point in the sequence? I did it as step 16, but maybe it should have been step 2. If we are rotating and stitching parts, is that best done before or after we resample and scale upwards? Who knows. Probably not much in it.



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