06 Aichi Val
This is a real world example. This Aichi Val plan was posted online here - http://www.rcgroups.com/forums/showpost.php?p=22770256&postcount=495 - on 19th Sept 2012 by aeromeddler. It is a very good plan, nicely scanned and in the form of a useful multi-page PDF (including article text pages) with a total filesize of 2.3MB. The plan was originally printed in the Aeromodeller magazine with a speckled background. This noisy background makes the plan difficult to read with the eye, larger in filesize than is ideal, and also it wastes more ink than we would like when we print it. In an ideal world, the plan would have a plain white background.
We want to remove all the noise from the background, whilst keeping all the useful detail in the plan drawing. We'll use the Dust & Scratches filter to do this. This technique is not perfect, so we will have to compromise between cleaning up on one hand, and keeping all the drawing detail on the other.
In this tutorial I am using Photoshop CS3.
1. Start by dragging and dropping the PDF into Photoshop, so we can have a look around. In the Import PDF dialog window, click the 'Images' rather than 'Pages' radio button, and then select just page 1 for import.
2. Ok, we can see that the image is a good clear scan, it's at 300dpi, and has been posterized and bitmapped into just 2 colours. It's all good - but that original print style with the speckled background sure is hard on the eye. Here's how it looks at 50% size:
3. Did I mention that I set the image mode to Greyscale already? Ok. And here it is again at full 100% size:
4. Let's talk about how we're going to do this. I'm going to call the speckles 'noise' from now on. Ok. Broadly speaking there 3 techniques we can use to get rid of this noise: First and most obvious, we can just remove the noise using the pencil tool. Here I've set the pencil to white ink and the brush size to 19px and I'm 'painting over' the noise slowly, by hand:
5. That's ok, and it will get us there in the end. But it's slow. Me, I know it will take me a whole evening of maybe say 4 or 5 hours to finish the whole plan, this way. So we need a better way to do this. The second technique is to somehow select and delete larger areas of noise in one go. Here I've set the paper colour to white and I'm using the rectangle select tool to grab an area of the canopy glass:
6. Then when I hit 'Delete', that rectangle is cleared of noise:
7. Irregular areas can be selected using the Polygonal Lasso tool. It's quite hard to see what's going on here, but if you squint you can see I have selected the whole of that same pane of canopy glass:
8. Then when I hit 'Delete', that area is cleared of noise:
9. Done. Ok, those are the 2 simple ways. Now let's look at the filter. But before we go and mess everything up, lets make a copy of this layer. In the layers window, right click on the Background layer and select 'Duplicate Layer'.
10. Hide the background and now get focus on the upper Background Copy layer. Now we can carry on working on this layer, safe in the knowledge we have a good clean copy tucked away underneath, which will come in useful later - trust me.
11. Now to start the filtering process, click on the top menu: Filter/Noise/Dust&Scratches:
12. A bit of explanation. We will use the 'Dust & Scratches' filter several times at a low setting, rather than using it once at a high setting. This seems to give the best results and to preserve the most detail. The lowest setting of all is with Radius=1 and Threshold=255. At that setting, literally nothing will change. I tend to use the filter at very low settings close to this. I mean I use Radius on 1 or 2, never more than 3. And for me the Threshold is only ever applied at 254, ie as little as possible. That's it. If want to go wild and crazy, try running the filter with Radius 5 and Threshold 100... you'll end up with an impressionist watercolour painting effect that's very pretty, but no use for plans.
It's fun to use. The preview window lets you try each step before you apply it. I spend a lot of time staring at this preview window whilst tapping the up and down keys on the keyboard to switch between 255 and 254 (ie on or off) then back again, repeatedly, so I can check the previewed results each time I'm about to apply the filter.
In this case, I've decided to up the stakes and do 2/254 for the first filter application. Here's the preview at 255 ie filter off:
13. Which when dropped one notch to 254 and applied, looks like this:
14. That was a big one, so now I'll do a few repeated uses of the filter in smaller steps at 1/254:
15. Yep, that's looking pretty good:
16. And again. To repeatedly apply the same filter over and over again at the same setting, the keyboard shortcut is Ctrl+F:
17. Nice. Ok, when using the filter on 1/254 repeatedly, at some point you'll end up finding all the tiny dots are gone, but there are still some larger spots of noise that are just too big to be filtered out at that setting:
18. So here, to tidy up, I'm setting the Radius up to 2 again and doing an apply at 2/254:
19. Outstanding. All nice and clean. Of course if we zoom out and check the rest of the plan, there will be many spots left to clean up by hand. That's fine. Now, I know what you're thinking. You're thinking... hmm, well, that's all pretty cool, but we've lost some detail now in the drawing... well, I like to think this is the clever bit. You remember step 10 and how we kept a good unspoiled layer safe underneath? Let's take a look and compare our two layers now. In the layers window, unhide the Background layer:
20. And now - this is hard to show you in a static screenshot image - I want you to sit and stare at the screen whilst you tap repeatedly on the show/hide icon for the upper layer. That way you can see the changes between the filtered and the unfiltered plan. Comparing between the two and deciding which part of each layer you prefer is the next step:
21. What it boils down to is this: we cut holes in the top layer to reveal the nice detail underneath. Here you can see I'm just roughly and quickly selecting an area inside the outline of the fuselage interior structure:
22. And now tapping the Delete key reveals more of the nice woodgrain detail in the lower layer:
23. That's about it. Just do more of the the same cut-outs around the rest of the plan, to bring back any lost interior detail. Then do a quick touch up of remaining spotty areas by hand. And we're about done. Do Layers/FlattenImage. The final stages are as always: Posterize to 2 levels, Bitmap at 50% threshold, Save as PDF.
This technique does not always work. Your mileage will vary. Depend on the ratio of signal to noise in the scan to start with also the dpi setting and a bunch of other factors.
Will add more notes in a while.
The finished plan is here: http://www.outerzone.co.uk/plan_details.asp?ID=3339