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Technical

July 2008

There’s no photo retouching challenge that you can tackle in a traditional darkroom that you can’t also easily hurdle using Photoshop CS3’s suite of advanced photo retouching tools. Once you’ve spent some time mastering Photoshop’s digital darkroom you’ll be able to tackle complex retouching challenges more quickly than you can by using traditional techniques.

Let’s kick off by looking at the key to Photoshop’s retouching powers – the humble pixel. Your digital photo is made up of millions of tiny squares (or pixels). It’s worth pondering on pixels for a moment, as these miniscule mosaic-like squares are the very building blocks of a digital photograph’s reality.

© George Cairns

Square pixels work like mosaic tiles and create the effect of smooth organic lines when viewed from a distance.

To have a close encounter with a photograph’s pixels grab the Zoom tool from the toolbox on the left of the interface (or press [Z] to select it). Keep clicking on the photo to zoom in. Eventually the [+] symbol at the centre of the Zoom tool icon will disappear, indicating that you’ve arrived at full magnification. You’ll be able to see the square pixels that make up your shot.

When viewed at the pixel level the image looks very crude. It seems quite incredible that your subject’s organic curved lines can be recreated from a combination (albeit very large) of coloured squares. All of Photoshop’s advanced retouching tools work by changing the colour, brightness and even location of these simple squares. By editing the shot’s pixels you can retouch any problem and re-shape the photograph’s reality in a convincing way - as if you’re re-writing a subject’s DNA to create a new creature!

To escape the blocky realms of the pixel simply double-click on the Zoom tool icon in the toolbox and you’ll see the shot at actual size. Alternatively you can click on the Actual Pixels or Fit Screen icons in the Options bar at the top of the screen. For an alternative way to access the Zoom tool’s various options simply right click (or [Ctrl] click on a Mac to activate the context sensitive pop-up menu. This contains the same zoom options that you’ll find in the Options bar without the need to move the cursor to the top of the screen. This context-sensitive pop-up menu changes depending on the tool that you’re using, making it a great way to speed up your image-retouching workflow.

© George Cairns

Counteract the keystone effect and abolish barrelling using the suite of pixel-pushing tools in the Lens Correction command.

Let’s take a look at Photoshop’s advanced pixel-pushing tools in action by throwing some typical retouching problems at the package. We’ll kick off with the common problem of lens-related distortions. When shooting a building from a low angle (and with a wideangle lens) you’ll end up with the vertical walls converging inwards lines instead of running parallel with the edge of the frame. You could try using a tilt-and-shift lens (such as Canon’s TS-E24mm f/3.5L, TS-E45mm f/2.8 or TS-E90mm f/2.8 lenses) to minimize this keystone effect, or you could play around in a traditional darkroom by tilting the photo paper to try and counteract the distortion. Photoshop provides an easier and faster way to tackle the perspectival distortion that's apparent in a photograph.

To straighten out the converging lines of a tall building go to Filter > Distort > Lens Correction. The Lens Correction command window will open, presenting you with a wide range of pixel-pushing tools. Pop down to the Transform section of the command’s interface. As the building’s lines will converge inwards towards the top of the frame drag the vertical perspective slider to the left to compensate for the keystone effect. The top image will tilt forward as if it’s on an adjustable board. A handy grid is overlaid on the photo so that you can make sure that the building’s re-positioned pixels run perfectly parallel with the edge of the frame.

Some lenses can also cause the shot to barrel outwards or inwards at the edge. The Remove Distortion slider in the Lens Correction interface enables you to counteract barrelling with ease. You can also use the Vignette sliders to lighten up darker edges at the edge of the frame to create an evenly lit shot.

Once you’ve distorted the shot to straighten the converging verticals you’ll notice that there are transparent pixels at the bottom of the image. You could drag the Scale slider to the right to zoom in a little and lose the transparent edges, but this enlarges the shot and runs the risk of adding blocky fuzzy artifacts to it. To preserve image quality hit [Return] to apply the changes and use the Crop tool [C] to remove these transparent edges without enlarging the photo.

© George Cairns

A Hue/Saturation Adjustment layer lets you target and remove colour fringes more effectively than the dedicated Chromatic Aberration removal tool.

Some digital cameras find it a challenge to focus different wavelengths of light onto the same spot on the camera’s sensor, which can result in blue, red or cyan colour fringes clinging to the edge of high contrast objects. This phenomenon is known as chromatic aberration, and the Lens Correction command has a slider designed to shift these fringes to hide them. If you’re editing a humble JPEG then this slider doesn’t work too well. The Chromatic Aberration slider in the Adobe Camera RAW editor does a much better job as it has much more colour information to play with.

To remove colour fringes from a JPEG go to the Layers palette and click the Create new adjustment layer icon. Choose the Hue/Saturation adjustment layer option. You can then target and remove specific fringe colours like Cyans by reducing their Saturation value. If there are other Cyan colours in the image that you want to preserve then you can paint a black brush [B] on the adjustment layer‘s mask to protect the corresponding parts of the photo from being altered. Masks are a great way off limiting your retouching to specific parts of an image.

© George Cairns

The Smart Sharpen command helps reveal hidden details without adding artifacts like blown out highlights.

One of the most common problems we encounter as photographers is soft focus. Photoshop uses tools like the Unsharp Mask command to create a sharper looking shot by increasing the contrast between adjacent pixels. This gives the shot more punch and helps bring out hidden details. If you push the Unsharp Mask command’s sliders too far you can end up with artifacts like harsh white or black lines (halos) clinging to the edge of contrasting areas. You can also end up with blown out highlights too.

There is a Sharpen tool [R] lurking in the toolbox. This brush-based tool enables you to sharpen specific areas by spraying the cursor over them. It’s not terribly effective and can end up adding noise style artifacts to the shot. For best results, and more advanced control, check out the Smart Sharpen command.

From its debut in Photoshop CS2 onwards the Smart Sharpen filter has undertaken a similar job to Unsharp Mask, but it offers greater control when sharpening pixels in lighter or darker parts of the image. By targeting sharpening to specific tones you can reduce the chance of adding artifacts to the shot as a whole. Go to Filter > Sharpen > Smart Sharpen. Use Amount to increase the contrast between edge pixels. Use Radius to limit the amount of pixels adjacent to edge pixels that will be affected. A low Radius setting (make sure you don’t go higher than 2.0) helps avoid dark lines appearing round sharpened areas and reveals finer details like hair.

The Smart Sharpen filter also has the edge over Unsharp Mask because you are actually able to specify which type of blur the image is suffering from. If your subject is blurred due to motion (perhaps caused by a panning camera or a moving subject, for example) then you can use the Angle control to tell Photoshop which direction the image is blurring in.

© George Cairns

A couple of clicks with the Spot Healing brush provide some digital skin care when retouching portraits.

So far we’ve examined how Photoshop’s commands and tools enable you to re-position a picture’s pixels to counteract the effects of lens distortion and change the contrast between neighbouring pixels to create sharper looking shots. These retouching commands help us to overcome the problems introduced by the camera so that we can create a more faithful reproduction of our subject. Another way to retouch a shot is to use brush-based tools like the Clone Stamp [S] and the Healing Brush [J]. These tools let you sample pixels from one part of the image and spray them over another.

For example you may have a blotchy sensor spot that's spoiling a sky in a landscape image. When you click on the unwanted spot using the Spot Healing brush tool [J] the tool automatically looks for a clear patch of sky adjacent to the unwanted sensor spot. It then transplants the clear patch of sky over the spot and merges the transplanted pixels with their new neighbours to create a seamless blend. This tool is also handy when tackling a portrait in which the model has a temporary facial pimple that needs retouching.

© George Cairns

You can take your retouching one step further and re-shape reality by cloning out distracting elements. Selection tools help you to isolate the area that you want to retouch.

As well as retouching a shot to remove camera-induced artifacts like chromatic aberration and sensor spots you can push the boundaries of retouching in a more creative direction by removing unwanted objects from images (like ugly telegraph poles blighting a landscape, for example). This dramatically alters the reality of the scene. Select the Clone Stamp tool [S]. Press [Alt] and click to sample an unobstructed patch of grass and then spray it over the unwanted telegraph pole.

The trick for the most effective, and by far the least visually intrusive, use of cloning is to sample and spray ‘little and often’. If you try to clone out an object in a single brush stroke you can end up re-sampling and re-cloning pixels. This can lead to repetitive patterns that clearly give the game away that the image has been retouched. It’s also a good idea to clone onto a new transparent layer. You can do this if you tick the Use All Layers box in the Options bar. You can then fine-tune your cloned pixels without altering pixels on the original background layer.

© George Cairns

In CS3 you can remove unwanted blemishes and sensor spots without losing a RAW file’s pedigree status.

CS3’s Adobe Camera Raw editor now has its own version of the Clone Stamp and Spot Healing brush tool. The Retouch tool enables you to remove sensor spots and other unwanted blemishes while working on a RAW file. You don’t need to leave the comfort and quality zone of the RAW interface if you need to do subtle re-touching. The Raw editor also allows you to crop and straighten a shot to improve composition. In theory you could do most of your retouching in the Adobe Camera Raw editor, though you’ll need to open the RAW file in the standard editor to access more advanced retouching tools like vanishing point (see part 1 of this series of Photoshop CS3 articles).

© George Cairns

The Raw editor’s Parametric curve sliders enable you to retouch the intensity of specific tones without losing control.

In part 1 of this series on Photoshop CS3 we looked at how the Level’s command’s sliders enable you to adjust a photograph’s tonal range. This is a great way to fix exposure related problems and produce shots with a healthy range of shadows, midtones and highlights. The Levels command has three sliders that let you tweak the value of a shot’s shadow, midtone and highlight pixels. A more advanced tone-tweaking tool is the Curves command. This enables you to place multiple points on a curve so you can target and tweak specific tones. This is a powerful way to adjust a shot’s highlights without messing with its shadows and mid-tones, for example.

The Curves command can be a tricky tool to master and it’s easy to end up over-doing your tonal adjustments and creating clipped shadows or blown out highlights. An easier but highly effective curve-based tool can be located in the Adobe Camera Raw editor’s Tone Curve pane. Click on the Tone Curve’s Parametric tab. Here you’ll find sliders that control points on the curve to alter a photo’s Highlights, Lights, Darks and Shadows. This is a more effective way to restore detail to a specific range of tones without messing with the image’s overall tonal range.

The beauty of retouching problem pictures in Photoshop is the fact that you can experiment safe in the knowledge that you’re not going to ruin your original source image. You can jump back through your last few edits using the Edit > Step Backward command. If things go totally pear-shaped hit F12 to revert to the last saved version of the image and you can then start retouching from scratch.