A More Complex Distortion Problem

The city and countryside of Chartres, France, are dominated by the magnificent cathedral. Visible from 15 miles away, the cathedral grows taller with each step closer one takes. By the time I reached the vantage point of this photo, I knew some perspective correction would be needed in Photoshop.

I set up my camera with 24mm wide angle attached on a tripod and used the self-timer to ensure a steady, long exposure in Program mode (about two seconds, I would guess). While I made several exposures, this one was the best but for some reason, the tripod head slipped a bit and left the cathedral on a slight tilt.

And its spires ARE soaring toward heaven as intended by its builders, but not in an architecturally pleasing fashion due to the camera pointing up.

Again, for this tutorial I have sent the image it its own layer (Command/Control-J), erased the background to white and created a larger canvas size.

With the image layer selected and unlocked, choose the Move tool (V) and then the Free Transform function (Command/PC: Control-T). The first step is to rotate the image to the right. I pulled down a guide from the ruler bar to the left edge of the lawn and judged my rotation to that.

Place the cursor outside the Transform box and it will turn into a Rotate arrow. Drag the arrow down and to the right to achieve the correct rotation. Do not click return.

Now it's time to correct the falling-away perspective. Click and hold the upper-right corner transform handle and hold down the Shift-Command-Option keys (Shift-Control-Alt). Now drag the handle to the right until the towers assume their proper perspective.

Note that the cathedral has become more squat. I drag down the center bottom handle to restore its original lofty height.

The image is now a free-form shape and needs to be cropped. Choose the Crop tool (C) and work from the narrowest corner of the important part of the image (lower right in this case). I wanted to include both towers in their entirety so my crop left a tiny wedge of the white background.

Fortunately, the sky is a nearly total black which makes for a simple application of the Clone tool (S), Clone in the nearby sky, working carefully with a smaller, hard paintbrush to work around the tip of the tower.

And there you have the finished cathedral in a lot less time than it took the original builders. I would I could show you some images of the stunning stained glass for which Chartres Cathedral is famous but our visit was accompanied by heavy overcast and rain. This night shot was the best I could hope for.

June 20th, 2006 | Jim Patterson | Photography, Tutorials | Comments (1)

Simple Photoshop Distortion Corrections

As a photojournalist, I've always been partial to my "normal" lens: the wide angle. Now, as a digital photojournalist, my wide angle attachment stays on my camera about 80 percent of the time, effectively cutting my zoom range to 24-85mm (approximately 35mm equivalent).

With the Macro mode turned on permanently, I find this is a setup that is ready for virtually any subject, except wildlife.

But wide angles do present some problems with image distortion. Point a wide angle up at a tall building and the building will seem to fall away in altered perspective. Here's a simple fix in Photoshop for that problem (it also works for distorted perspective when the lens is pointed down).

Here's a shot of Singapore's skyline from Boat Quay. Even from a distance, the downtown buildings were so tall that I had to tilt the lens up to get them all in the image. Note that they tend to be leaning in as if Singapore isn't built on a firm foundation (which it isn't).

For purposes of the tutorial, I've sent the image to its own new layer (Command/PC: Control-J) and unlocked it. With the Move tool selected, I choose Free Transform (Command/PC: Control-T).

Next, select the upper right corner handle and click and hold down, then hold down Command-Option-Shift (Control-Alt-Shift) and drag the handle to the right. As I do so, the left corner moves out as well, correcting the tilting perspective.

While this technique brings the perspective to a normal view, it also has the effect of shortening the buildings. To correct this, grab the center bottom handle and drag it down until the buildings look their correct height.

When you click the Return key, the image will be corrected and some portions of the image will be automatically cropped.

Now, on to a second kind of distortion. My Nikon WC-E24 lens (the older, smaller in diameter version) is notorious for Barrel Distortion (perpendicular images bowing out at the edges like the sides of a barrel).

For most images, I live with the effect. Also, I can use Andromeda's Lens Doc plug-in for precise correction. But here's a simple correction technique in Photoshop.

Note that the pillars on each edge of this picture have a graceful bow to the outside. I've sent the image to its own layer (Command/PC: Control-J) and erased the background image to white, and finally increased the canvas size to create a white border for this tutorial.

The image of Man Mo Temple in Hong Kong doesn't have any vertical lines in its center and the distortion of the rafters isn't as noticeable as the vertical pillars. This is an ideal image for the Pinch filter.

Choose Filter>Distort>Pinch. For my 24mm lens, I've found a factor of 9 pixels perfect. You may wish to experiment with a lower number for your particular image but if you go over 10, perhaps it's time to shop for a new lens.

Now you can see the effect of the Pinch filter against the white background. Unless you like wavy edges, use the Crop tool (C) and trim the image down to square edges.

Next week, we'll tackle a slightly more complex variation of wide angle distortion.

June 20th, 2006 | Jim Patterson | Photography, Tutorials | Comments (0)

The Shadowy Face of The Luminosity Mask

Last week we learned how to use a Luminosity Mask (Command+Option+Tilde [~] or PC: Control+Alt+~) to emphasize highlight details in ultra bright situations such as snow on a Swiss Alp.

But the LuMask is more than a one-trick pony. The more you use it, the more ways you'll think of to use it. For this week's demo photo, we move from the Jungfrau to my back yard (which is a lot like the Jungfrau, my neighbors say). The shot is of azaleas blooming with my neighbor's unsightly fence in the background.

While the image is basically well exposed, it could stand some beefing up in the highlights and I'd dearly love to make the fence go away. LuMask to the rescue.

First, I'll make a LuMask by using the Tilde sequence mentioned above. I've made this into an Action so F4 does the job without getting carpal elbow. As you can see, the selection looks just like any other marching ants pick.

I send the mask selection to its own layer (Command+J/Control+J). For demo purposes, I've isolated the mask layer and run an extreme Levels so it shows up in the screen shot. In reality, it's quite faint and looks mostly gray.

To beef up the highlights, I set the LuMask layer's blending mode to multiply. It seemed a bit too beefed up so I decreased the layer opacity to 77 percent. I cut a chunk out of the mask layer for demo purposes in the screen shot above.

After flattening the image, I created another LuMask but this time Inversed it (Command+Shift+I/Control+Alt+I). The screen shot above shows how it selected the green leaves and shadowed fence in the background.

Now, here's the other face of the Luminosity Mask. If I set the Mask layer to the Screen blending mode (instead of Multiply), the detail in the shadows pops out. In this case, you can now see the unpainted grain of the fence which does nothing at all to help the picture. Still, if you need shadow detail, LuMask plus Screen is the way to go.

So to improve the image, I set the Shadow LuMask to Multiply which made the fence vanish and darkened the leaves. What's more, I ran a Command+J on that layer to make a second mask, then lowered its opacity to about 50% to get an azalea that looks as if it were shot with studio lights.

I hope you find the Luminosity Mask technique as useful as it is to me. BTW... you'll find the Tilde key on the far left of the keyboard's numbers row.

June 20th, 2006 | Jim Patterson | Photography, Tutorials | Comments (1)

Recovering Lost Highlight Detail

Tips and tricks are the trading cards of Photoshop. Scott Kelby makes a good chunk of his living teaching and writing about them. Photoshop techniques, tips and tricks are like hamsters... they beget rapidly with each new user adopting a variation.

Currently, the hot technique is Luminosity Masking. My buddy Jim DiVitale calls it "the claw" for its five keys plus elbow keyboard command. My variation has been assigned an F4 action. Now everyone is on the Luminosity Bandwagon. It's been one of my favorite imaging tools since I learned about it at Photoshop World 2000. Here goes:

Most digital cameras have incredible exposure metering capabilities, with many boasting multiple area matrix metering. However, with extreme contrast scenes, the highlights are the first to go. If you adjust in Photoshop to recover highlight detail, shadow areas and midtones are often affected adversely.

Attempting to select highlights by selecting with the Magic Wand or using the Similar command do work, to a certain extent. But the results are often artificial looking. Luminosity Masking to the rescue!

I'm using an image I made of Switzerland's Jungfrau a couple of years ago. As is typical, matrix metering resulted in a good overall exposure with a deep blue sky and washed out detail in the highlight area, namely the snowy ledge beneath the mountain.

The secret behind this tip is to select the luminosity of the image, which will vary from picture to picture. This is done by using the keyboard command Command+Option+~ (tilde) [PC: Control+Alt+~). This results in a selection of the highlights based upon that image's luminosity. Since luminosity varies throughout an image, the selection is effectively self-feathered.

The screen shot shows the luminosity selection which is basically composed of the snowy areas on the mountain and the bank beneath the mountain. In addition, highlight luminosity is present in the clouds. In my judgement, I wanted the mountain and clouds to remain unchanged and just increase the detail in the snowy bank.

So I sent switched the luminosity selection to Quick Mask and used the airbrush set to black to paint out the selected mountain snow areas and clouds.

Switching back to the selection mode, I sent the selection to its own layer (Command+J or PC: Control + J) and set the layer's blending mode to Multiply, causing an increase in the highlight detail in the snowy bank.

The final screen shot shows the end result with a stripe cut out of the Multiply layer to illustrate the difference between the raw image and the enhanced Luminosity Masked image. I think you'll agree that it makes a difference.

The beauty of a Luminosity Mask is that it selects highlights as they occur in the image, with feathered or graduated edges.

Next week: the other face of Luminosity Masking.

June 20th, 2006 | Jim Patterson | Photography, Tutorials | Comments (1)

Panoramas: When The Terrain Doesn’t Cooperate

When last we visited the exciting world of making panorama images with Photoshop, I used a relatively common subject as an example: a level drawbridge over Florida's Intracoastal Waterway close by my home. But the best panoramic views are often from a high vantage point looking down. And these present a problem of distortion. In this column, I'll deal with combining three views of France's Dordogne River shot from extreme angles.

The actual view encompasses a bend in the river sweeping by the village of le Roc Gageac. Using the widest angle of my zoom lens, I shot three images with about a one-third overlap.

I followed all the steps outlined in the first pano column: resizing the photos; putting each of them on its own layer; and creating a larger canvas size to accommodate the overall panorama.

While my image was resized to 3 inches in height, I set the New Canvas Size to 5 inches high for a little wiggle room. The canvas width, set from the left center, was 10 inches. Note that I made the background layer black in order to see the rather washed out sky as I worked.

All three images are now on the background in separate layers and have been overlapped using the lower opacity layer technique previously described. Note that each layer is slightly higher than the previous one, due to the fact that I attempted to keep the center of the image constant with each shot.
Using Levels (L), I matched the colors of each layer as closely as possible, using adjacent foliage colors. In figure 2, you should be able to see the vertical lines where each image overlaps. The first step is to use the Eraser tool (E) to eliminate these contrasting vertical butt lines and blend the image as realistically as possible.

I'll reiterate that the goal is to create a detailed image of framed peripheral vision but not to attempt to fool the viewer into believing it was made with a single exposure.

I set the Eraser tool's options to Airbrush and selected a 100 pixel soft brush tip and 50% pressure for my Wacom tablet. Selecting the top layer (from the right), I began painting gently over the butt revealing detail from the layer beneath. In the screen shot, the upper arrowhead points to the untouched butt line. The lower arrow shows where the river has been blended in a sharp curve that isn't really there but it's the impression that counts.

Don't attempt to get perfect blends by painting out with the eraser. The blends get refined even more in the next step.

After flattening the image, I use the Crop tool (C) to create a single image. Now it's time to fine-tune the panorama by cloning out duplicate details.

The close-up screen shot above shows that the houses of the village directly below my vantage point have been duplicated due to the extreme angle of view. Eraser painting here would have just revealed more duplicate detail. Instead, I select the Rubber Stamp tool (S) and from its options, use the same airbrush tip and pressure.

I decided to cover up the closer set of houses by cloning foliage. Using a variety of trees of the same shade from different areas as my target point, I carefully brushed in trees to eliminate the roofs. Here, you must be careful not to just sweep the clone tool down from the target, creating a repetitive pattern. Instead, select different areas as a target by Option (PC-Alt)-clicking.

Now the village is a single set of houses. The residents might be a bit miffed that I've messed with their property lines but that's life in the pano world.

The horizon and skyline present a different challenge. I used the clone tool to clone sky into the areas where the hills did not meet, then targeted the hilltops to create a new horizon. Due to the soft pressure used with my Wacom brush, the overall effect is of a cloud or fog bank coming through the gaps of the hills.

Once you get used to shooting panoramas, you'll see scenes where the subject matter screams for pano treatment but the terrain is definitely working against you. This was the case in Le Baux, an Iron Age fortress and medieval village in Provence.

Here, I chose to make a continuous set of images matching one to the next but not trying to maintain an impossibly level horizon. If I had cropped the entire image to a rectangular frame, the effect of the steep hillside and surrounding cliffs would have been lost.

Instead, I matched the images in stair step fashion and then outlined them with the Pen tool (P) to create the irregular frame. Making my paths into a selection (Command [PC-Control]-Enter in 6.0, just Enter in 5.5 or earlier), I then sent the image to its own layer (Command/Ctrl-J) and then gave it a drop shadow.

I really like the effect and so do others. It's sold several times.

June 20th, 2006 | Jim Patterson | Photography, Tutorials | Comments (1)