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STITCHING PHOTOGRAPHS...

We have received requests for a tutorial on stitching photos together.

Since there are some basic differences between stitching photos

and stitching scans, here we go...

First, we're going to put together two snapshots taken in Chicago of

the Michigan Avenue bridge. The top photo has one of those ever-present

elements in quick snapshots: the dreaded fat finger. The bottom photo

is fine, but doesn't capture the whole scene. Hopefully, we'll have a

complete and usable picture when finished, in a vertical format.

Later, we'll assemble two pictures taken of Lake Michigan

beach from the Indiana Dunes National Lakeshore, looking west

toward Chicago. That will look more at color and tone corrections.

First, the bridge... Here are the two original shots:

The first step is to create a new Photoshop document large enough to

hold both images in reasonably good register, but with some breathing room

for adjustments. Save the new image, and work on a copy in case what

we try doesn't work well enough, and a new approach becomes necessary.

By lowering the opacity of the top image we can see what we're in for - the

parallax effect on the building is going to cause big problems. The

easiest thing to do would be to only use the very top of the top image

(to fill in the fat finger area), but I like position of the flags on the

top image better, so let's try to stitch them together to include

those flags. (*In this example, there is no rotation adjustment

needed. If you do need to rotate one of the layers to align it to another, an "automatic" numeric procedure is covered in tutorial five.)

The first step in correcting the parallax effect is to activate the top layer,

and use "Transform" (command/control-T). You'll get a box around the

layer with handles at the corners and midpoints. (There will also be a

"register" mark at the center of the box. This can be moved to any point

in the image; even outside the box. If you move this mark, you're resetting

the center point of rotation. You can then click anywhere outside the box

and rotate the entire layer around the repositioned center point.)

The key to aligning the image via Transform is to use the command (control)

key to change the effect of moving the handles. When you hold this key down, it allows movement of the handles independent of the others. For instance, you can skew at the midpoint handles and adjust perspective at the corners. Other

handy features to know are that if you hold option (alt) while moving a handle,

the adjustments will be made in symmetry. Also, if you hold Shift while moving a

corner point, the whole image is scaled in proportion. If things get out of control,

just hit the escape key to deactivate the transform box and start over.

If you find that the window is limiting your adjustments, enlarge it without changing the view size. You can then work with the handles

outside the actual image area like this:

Here is what the image looks like after the top layer has been transformed to

match about as well as can be expected. Care has been taken to match the critical areas of the layers - the top of the tower and the bridge. In this case,

that's about all we can hope for at this point. When you're ready, press return (enter) and the transformation is completed. Save a copy before continuing.

Now we do a little "cheating" to get things looking good. I happen to know that

these two pictures were taken from positions about fifteen feet apart, so there's really no way they will ever line up perfectly. (Yes, it's my fat finger - and you thought I was doing something wrong.) What we'll do is erase from

the top layer across areas of little detail, stopping at areas that do line up

correctly. Here's what's left:

And, here's the image with both layers visible:

Finally, merge the layers, retouch the sky as needed,

and make your color corrections.

Here's the final image - pretty good for starting with

pictures taken at two different locations:

Now, for the second part of the tutorial; stitching the beach shots...

Here is what we'll work with (the buildings you see are actually

industrial areas south of the city):

These are, at least, taken from the same spot. There are slight differences

in tone and color; more typical of landscape panoramas. An added difficulty

will be finding a way to merge the moving waves into one image, while

keeping the essence of the scene completely natural. It's really easier than

it may seem at first.

The first process after creating a new canvas and aligning them roughly

where they need to be is to rotate both layers to the same horizon line.

As covered in tutorial five, you'll want to measure the angle of both layers

and let the program do the work automatically. Here's the dialog that comes

up (you can see the measure tool line behind the dialog box):

This image shows the two layers in position:

As mentioned earlier, the tone, the color, and the waves create a very

obvious seam. This image shows the seam up close:

The first thing I've done is to use the levels adjustment to bring the

majority of the color and tone more closely in sync. If you have an image

that doesn't respond well to the levels adjustment, use curves instead - it

is more suited to fine adjustments. Levels worked well here:

(When stitching panoramas, you can only go so far with sweeping adjustments

like levels. There are going to be many areas that require a lighter touch and

specific tools. As Photoshop skills increase, these tools and adjustments

become second nature. In fact, there are usually a few different

ways to achieve similar results. That is when you start to feel real

excitement about the program, because the depth and subtlety available

is truly remarkable.)

For the next step, a selection of the sky and water was made to adjust

only those areas. The sand is already pretty close. This image shows the

selection in quick mask mode (simply press "Q" after the selection is made):

The main reason to enter quick mask mode is so that we can apply the

Gaussian Blur filter to the selection to soften its edges and to blend the

upcoming modifications more smoothly. A blur radius of 75 pixels

is applied to this selection:

Here is the visual effect of the blur filter on the selection (press "Q"

again to exit quick mask mode and work with the modified selection):

Again, levels is applied, but only to the selected area. This brings the sky

and water even closer to a match on both layers:

Now, to blend the sky across layers, activate the right layer and using

dodge with highlights set to the minimum amount, we dodge the area of

mismatch at the top of the image. Even at the lowest setting, it's too much.

Don't worry, though, because we can then fade the dodge application by

pressing Command-Shift-F (Alt-Shift-F) and using the slider to get the

result we want as seen here (check the preview box so you can make

the adjustment precisely):

A couple more operations (dodge, burn and saturation of midtones),

and the sky matches up well:

Here is the complete panorama prepared as well as possible for

the next step; blending the water and touching up:

The final step to blending this image is to use the erase tool at different

sizes and opacity to remove parts of the left layer. This takes time, and

you'll want to work in very close to get the best effect. Use the history

palette, layer opacity variations and basic trial and error

to achieve a good result.

Sand: Remove and blend ruts and prints, shadows and highlights

to obscure the seam line.

Sky: A light erasure with a soft brush helps to get a smooth gradation

from one layer to another.

Water: Erase until an area of similar shape and movement allows small,

"woven" waves that appear natural. A little artistic license is needed,

but the erased areas really get the job done.

Here's what is left after working it over:

As a final step, some hue and saturation adjustments were made

and the sky was blurred a touch. Here's the final:

Someone would be hard-pressed to find the seam - even in the waves.

Click here for a printer friendly version.

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