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Two Camera composite

Using Photoshop CS3 to autoalign By Ko Maruyama
You don't have a tripod or a willing volunteer who will take your photo for you.  So one person gets up, take a shot, and then a different person gets up and switches with you for another shot.  "We'll just fix it in Photoshop".  Yeah?  Yeah sure!

You could always line up the images with previous versions of Photoshop, and truly there are probably 100s of ways that you could do it, but in Photoshop CS3, it's so much easier than it ever has been in the past.

With a little preparation, you won't need to ask some stranger to come up and take your group picture ever again.  It might be a fun exercise trying to get the images to line up too.  What kind of multi-shot composites will you come up with?

Here is the long way: 11 steps.  ;)

1. We want to get the left image into the same perspective as the image on the right.  You could simply cut/paste, but if you want to get closer to the correct perspective from one picture to another, Photoshop CS3 makes it really easy.

click on these images for larger views

2. Move the two photos into one document.  You can do this by dragging one of the pictures into the open document of the other picture.  Make sure that you have the footage you want to replace on top (we want to see it an align it).

3. There are several subjects in each of the two shots that we can use to align the two layers.  The table itself, with the red borders makes a perfect element for Photoshop CS3 to find and auto align.  Even if some of the objects are obscured, it doesn't matter, as long as they haven't been moved around.  If someone moved the take-away boxes or the cheese shaker, this would be a little harder to pull off.  It's something to keep in mind if you're going to attempt this later.

4. Make sure that you have two layers (floating layers) and not a Background selected.  You can copy it, or simply double click the layer so that it isn't a Background anymore.  Photoshop CS3 will use alignment to modify the position the layers - but we only have two layers, so it's the topmost layer that gets transformed.

5. With the  move tool highlighted, and multiple layers selected, you'll get an option to align those layers in different ways - you can align them, or if you have more than 2, you can distribute them, but at the end of the column you'll see the two heads next to each other.  This will allow you to give Photoshop full control to auto-align the selected layers in various ways.

The first selection in the dialogue box is "Auto" which will allow Photoshop to make any kind of transformation needed in order to create an image with similar camera projections.

6.   Once you click okay - you'll see that Photoshop has done a pretty good job modifying the image.  The more you've moved the camera off axis, the more distortion might be introduced into the second layer.  You can see in the image below, the table's lines have been lined up perfectly, but the distortion that has been created in order to make it so is huge.  Because there's a lot of distortion, the girl appears to be about 3' tall (maybe she is).

7.  You can do this whole thing simply with FREE TRANSFORM (under the edit pulldown menu), but it's so much easier with the AUTO ALIGN tool.  But even if you use the AUTO ALIGN tool, you may have to tweak it a little bit using FREE TRANSFORM anyway.

8.  Click ENTER to accept the transformation (or double click), then head over to the lasso tool, and draw a quick selection around the girl.  Doesn't have to be perfect, you can change it later.

9. With the lasso selection still active, open up the LAYER WINDOW (F7), and at the bottom of the window, you'll see the icon (the little white circle in the black box).  Click that to to make a LAYER MASK, and it will be created from the selection you've made with the lasso tool.  You can always use other tools later to finesse the mask shape.

10.  Now you can see that there are parts of the girl missing when the layer is forced into a similar perspective.  Yeah - it looks right now, but there are parts of her that just don't exist.  You could crop the entire image to cut off the bottom and right side of the picture, but if you want to keep the entire photo...

11.  you'll need to either take a separate picture to slide into the same position (using only free transform to match), or you can paint the missing parts in!

It's a lot easier than it looks in 11 steps, but you should be able to pull it off in about 30 seconds once you get the hang of it.  I think it'd be cool if you'd tried to BREAK the process.

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Ko Maruyama is a freelance animator in Los Angeles.  In addition to working on film and broadcast animations, Ko teaches at Pasadena's Art Center College of Design - focusing on motion design.  When working, writing or testing software allows, you can find him lending a hand in the After Effects board and lurking among the Cinema4D, Visual Effects and Photoshop posts within the DMNForums.
Related Keywords:tutorial, adobe photoshop Cs3, digital pictures

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