Joining Scans of Oversize Artwork

How often have you had artwork to scan that was larger than your scanner?  Have you perhaps photographed your work instead, then been disappointed with the results?  All is not lost.  Your scanner can still be used and the results are nearly always better than using other methods.  Just scan your work in pieces then stitch them together again.  How?  Read on......

Simple is often best...

The bad news? There isn't any although I realise you may be questioning the quality that that can be achieved (and probably my sanity - you won't be the first). Well, even the humble MS Paint can produce excellent results, but I should say right now that we are not trying to scan at mega-pixel resolution for Fine Art printing — for such scanning you should be paying for professional expertise. No, these scans are primarily for website use or perhaps home-produced brochures or greetings cards where the image is greatly reduced. All the illustrations of my Limited Edition prints on this website were produced this way - and there's not a join to be seen!

But don't be fooled into thinking that basic software produces basic results. Excellent joined images can be accomplished at high resolutions. All of my Limited Edition prints are stored as 300ppi greyscale TIFF images, all have been joined using Adobe PhotoDeluxe (and lately by Photoshop 6) and all have invisible pixel-perfect stitching.

The basic kit to SuperPic...

I should mention that there are specific programs available for joining images.  Epson's Spin Panorama is one example; designed to join successive photographs of a scene into one long panoramic image.  Personally, I would compare this type of program to building a webpage with a WYSIWYG editor (it gives a very good approximation) against hand-coding the HTML, which gives total, pixel-perfect control.

Five steps to Heaven...

Making your scans...

Ok, let's get down to it.  Scan #1: Top, left hand end of the print and scanned in greyscale.  There's no point in scanning graphite pencil work in colour and by discarding all colour information your file size will probably be reduced by two thirds - this is important as all five scans may add up to 30MB or more.  Give your scans useful names - I use "pic_tl", "pic_tc" etc - to designate "top left", "top centre"...

Remember - your second scan must overlap the first and the third scan must overlap the second - it doesn't matter by how much.  Similarly, when you turn the drawing through 90° to scan the bottom edge, the drawing must be exactly square to the edge of the glass and the scans must overlap each other and the those above.

With the instruction to "keep everything square" in mind - scan all parts of your image, naming and saving them all as separate images for now, then read on.

Basic techniques with MS Paint...

Step 2:  Note the width of the image as it is now (that's 384 pixels in this case as I've reduced the original size so you can see it better).  Multiplying this by the number of scans across the image (three in this instance) will provide more than enough width because the three actually overlap.  If, like me, you have additional scans across the bottom, you need to increase the depth of the image also.  From the top menu select "Image" then "Attributes" and change the dimensions to your new figures.  Here I'm changing 384 to read 1150 and the depth from 590 to 650 pixels.  Click on OK and your new enlarged canvas will appear.

Step 3:  Open the next scan (the central one), press your CTRL and A keys together (CTRL+A) to select the whole image then CTRL+C to copy it.  Instead of the keyboard, you can, of course, use the Edit menus or the icons on the main toolbar for this.  Now re-open the "Master" image and, if you can't see the right hand edge, scroll sideways until the picture part is only half showing at the left hand side - you'll see why in a minute.

Paste your copied image by pressing CTRL+V or using the menus.  You'll notice that your cursor has changed to a four-pointed star.  You use this to move the pasted image - just left-click, hold the button down and slide the segment sideways. Slide it too far left (pictured above) then slowly back until you almost join the images together.   Now pick an area of activity, one where you can see if the two are joined perfectly - here I'll use the dog's head - then carefully position the segment so it joins seamlessly to the first one.

Finally, when you're satisfied, click anywhere outside of the image and the two will combine.  If you've made a mistake press CTRL+Z to undo it (or use Undo on the Edit menu).  And if one segment is a little darker than the other, complete the join as described, zoom right in and use the airbrush tool to spread the lighter tone across the join.  If the tonal differences are too great, this is where MS Paint will fail you as it doesn't allow you to change the contrast or brightness settings.

Using the flexibility of layers...

This system offers many advantages over the more basic MS Paint but here I'll concentrate on just two - the ability to choose between two join locations and a tool that can blend an obvious join.

Step 1 : First, if you are using Adobe PhotoDeluxe click on the "Advanced Menus" text at the bottom of the Open Photos bar.  Now click "View" then "Show Layers" and in the layers palette, drag the layer containing the latest image to be pasted to the top of the stack.  This is to ensure that, when moved, it overlays the previous image and doesn't slide beneath it.
Step 2 : Zoom in to an easy place to match the two halves - here I've chosen the head again.  Zoom in as tight as you need to then look for at least one identical element in both halves, click within the half to be moved, drag it over the first half and carefully move it into its correct position.

Step 3 : When you are satisfied that the two halves are correctly matched, release the mouse button and click outside of the image.  If the join is at all obvious or needs to be blended a little, first try checking the alternative position of the join.  Remember that you have one independent layer on top of another and an area where they overlap.  If you click in the first layer this will temporarily bring it to the top exposing the other edge of the overlap.  If this looks better then drag that layer (in the Layers palette) to the top of stack.

Disguising the join (part 1)...

Using layers in Adobe Photoshop 6...

If you have been able to try some of the ideas given here, using anything other than Photoshop, you'll be aware of the sheer, hair-tearing frustration when you attempt to nudge a segment just one last pixel up or down to achieve perfection......It always moves just one more!  The mouse is rarely good at such minute alterations but here's where Photoshop comes to your rescue.  Photoshop possesses the ability to position with pixel perfection because, instead of just being able to drag the layer with your mouse, you can also use your keyboard's arrow keys.  With these you can nudge the image in any direction, one pixel at a time.  And you can zoom in and out as you are doing so.

There is very little indeed that cannot be successfully accomplished with Photoshop and it is not my intention here to catalogue all the available tools - there are plenty of online forums, websites and discussion lists to give you all the information you need.  I will, however, attempt to cover a few of the basic tools that substantially assist with the joining of scans.  I should point out that many of these tools are also available in PhotoDeluxe although they are not quite as flexible.

Disguising the join (part 2)...

Horror story 1 : Here I have artificially darkened the right-hand layer and faded one edge.  These sorts of problems are not unknown and can often be tackled in a number of ways.  As we have a reasonable width of overlap I would begin by deleting the light-toned band using a soft eraser.  Enlarged below to 300%, you can see that the under-layer is now showing through as I work my way down with the eraser...

All that remains now is to adjust the brightness of the dark segment.  This can be achieved by using the Brightness and Contrast controls, the Levels feature or the Curves.  And for greater security you can apply any one of these to an Adjustment Layer, which can be turned off if required or altered at will without causing permanent changes to the image layer.

Horror story 2 : Here's part of a picture I received for inclusion in a website, already joined and merged into one image. The join wasn't too noticeable in the lower part of the image but, I'm sure you'll agree, it's extremely distracting in the sky.  The only action open to me here was to use the few good parts of the sky to repair the rest.  For this we can either select the parts then copy and paste them into place (the only available method in MS Paint) or use the splendid Clone tool.  The Clone wins hands down!

This is one instance where I prefer to use the Clone tool in PhotoDeluxe - it is more intuitive in operation than the more complex version in Photoshop.  Just select the tool, choose the hard or soft edge version, drag the "target" on top of the area you want to copy then click where it is to be copied.  As you move your mouse around you will copy the area under the cross that travels in sympathy with the brush.

If you're using PhotoDeluxe, release your mouse button often and occassionally save your work - it does not possess the multiple Undo steps of Photoshop and you may need to to "Revert to last saved" at times to delete errors.  

There are many other invaluable tools available but one worth singling out is the smudge tool.  You may be wondering why I didn't use it to blur the line in the sky?  Well, it's great for flat. smooth tones but not for broken or pitted surfaces such as this watercolour sky.  I'll show you... this is what a smudged sky would look like....

I've left the top edge un-smudged for comparison.  Overall it looks OK but it in no way represents the surface of a watercolour painting.

As with most things in life, the more you try something the easier it becomes.  Even keeping track of the layers you're using can be troublesome at times but it won't be long before you learn to carry a picture of the structure in your mind and can manipulate each element at will.

Happy joining...!