A Photoshop tutorial for photographers- Continued

Figure 13

Remove dust and scratches

Dust artifacts are inevitable when scanning images, either with a flatbed or a film scanner. When scanning slides the artifacts show up as black specks. When scanning negatives or photos they show up as white specks. Digital SLR’s eventually accumulate dust on their sensors, resulting in dark blurry dust spots in the image The process of removing these artifacts is called cloning and the tool used is the “Clone Stamp”.

Use of the Clone Stamp Tool

The Clone Stamp Tool is selected by clicking on its icon in the toolbar (figure 13). Notice that its icon looks like a rubber stamp as used with an inkpad. Think about how you use an inkpad stamp. First you ink the stamp by stamping the inkpad. Then you apply it.

The Clone Stamp Tool in Photoshop works in a similar two-step fashion. First you make a stamp of the part of the image you want to copy by holding down the Alt key while clicking in the image. Look for an area in the image with similar color and detail, usually right next to the artifact. Then release the Alt key and click where you want to apply the stamp.

What follows is the classic cloning procedure. It can be used to remove wrinkles, phone poles, and the annoying tourist who wouldn’t get out of you picture. You can even clone from one image to another. For now we will show its basic functions and how to use it to remove dust and scratches.

To remove dust and scratches using the Clone stamp tool:

1. Begin by creating a new layer. Always use a separate layer this allows mistakes to be erased at any time. This layer must be above any adjustment layers. If the cloning layer is below an adjustment layer your cloning will be lighter or darker than the image. So click once on the top adjustment layer to make it active. Then click on the new layer icon at the bottom of the layers pallet. A new layer is added above your active layer. Click on the new layer to make it active.

2. Click on the Clone Stamp Tool in the tools pallet. On the tools preferences check “use all layers”, and “aligned”. “Use all layers” allows cloning on a separate layer. “Aligned” maintains a constant distance between the area sampled and the area cloned. If “Aligned” is not checked the original sample point will not move until a new one is created by Alt clicking.
Adjusting the brush size controls the size of the cloned area. I recommend using a small brush size with a feathered edge just large enough to cover the width of the artifact. Where the length of the artifact exceeds the “with”, click multiple times to completely stamp over the artifact.

3. Set the image at actual pixel size. With the zoom tool selected right mouse click on the image and select actual pixel size (figure 14). As an alternative use the keyboard shortcut “Ctrl Alt 0”. With actual pixel size one pixel in the image equals one pixel on the monitor. This produces the most accurate preview.

4. Start cloning by holding down the alt key and clicking next to a dust spot in an area with similar color and detail and then releasing the alt key and simply clicking on top of the dust spot. When alt clicking the cursor changes to the Clone stamp icon. When cloning the cursor changes to the brush icon. This sets the starting point for the pre sampling. Move on to the next dust spot and without using the alt key put the cursor over the dust spot and click. Notice you did not have to alt click this time, Photoshop will do it for you. As you move around the image Photoshop will continually pre sample maintaining it’s exact distance because the “aligned” was checked.
If you find a clone doesn’t match choose the eraser tool by clicking on it once and then holding down the left mouse button erase the mistake. Reselect the Clone Stamp, choose a new area to sample from, hold down the alt key and click to establish a new sample starting point. Click on the dust spot and continue in like manner until all spots are removed.

An example of using the Clone Tool to clean up an image is shown below. Notice that the dark rotted areas on the lower half of the leaf (figure 15) have been removed in (figure 16).

Sharpen the image

Let me first dismiss the myth that sharpening in Photoshop can fix an out of focus or blurred original image, it cannot. What it can do is restore the sharpness lost in the capture process. Scanning software often has provisions for sharpening built in, but I have never found it to be as effective as using Photoshop. If you are using a digital camera it may also have on board sharpening but it won’t be able to match Photoshop’s versatility such as selective sharpening using an edge mask, which is what we usually use.

Preparing for sharpening

Before sharpening it is recommended that you flatten your image. Our image now has four layers: layer 1 the background, layer 2 a Levels adjustment layer, layer 3 a Hue/Saturation adjustment layer, and layer 4 the cloning layer. If sharpening was applied to just the background layer the image pieces on the cloning layer would not be sharpened. To sharpen the entire image the layers must be combined or flattened.

Our images typically have several adjustment layers that we prefer to leave available for future tweaking. One method is to leave our adjustment layers open and instead make a copy of the image and flatten that copy. We then sharpen the flattened copy. The following is a trick to take the flattened copy and add it to our original image as the top layer. This way we only have to save one file. The trick is as follows.

1. Choose Image, Duplicate this will produce an exact copy of your current image (figure 17). A dialogue box will appear for naming the file (Figure 18).

Figure 17

Figure 18

Figure 15 “Before Cloning”

2. Using the duplicated image flatten it by clicking on the circle with the arrow in the upper right hand corner of the Layers pallet as shown in red in (Figure 19) and click on flatten image.

3. Choose Select, Select All (Figure 20).4. Choose Edit, Copy.

5. Now close the duplicate. We normally do not save this copy.

6. In your original image select your top layer by clicking on it once, then click the new layer icon at the bottom of the layers pallet.

7. Choose Edit, Paste

8. What you have done is created a sum of all the steps you have already done in one layer. Your original image with its adjustment layers remains (figure 21)

Figure 19

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Figure 21

Using Unsharp Mask

Photoshop has several sharpening filters but the only one to use is “Unsharp Mask”. It is found in Filters, Sharpening, Unsharp Mask (figure 22).

Figure 23

The filter has three sliders: amount, radius, and threshold. The amount is the intensity of the sharpening. The radius is the thickness of the sharpened edges. The threshold determines the level of detail at which sharpening will be applied. The following are starting points for slider settings. Settings will vary by image and taste (figure 23).

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Figure 24

2. Choose Filter, Stylize, Find Edges (figure 25).
The Find Edges Filter produces a sketch like image finding all the edges.

3. Press Ctrl+I or choose Image, Adjust, Invert (figure 26).
Find Edges produces black lines against a white background, however we need white lines against a black background to produce a selection.

4. Choose Image, Adjust, Brightness/Contrast
Adjust the sliders to separate the white from the dark, what will be selected and what will not.

5. Keeping in mind that what is white will be sharpened, choose the paintbrush with black for the foreground and paint areas such as skies that need no sharpening. You are looking to eliminate the white in those areas.

Figure 26

6. Choose Filter, Noise, Median (figure 27 and 28).
Enter a value of 2. This smooths the selection lines.

7. Choose Filter, Other, Maximum (figure 29).
Enter 4 for the radius. This thickens the edges or expands the selection area (figure 30).

8. Choose Filter, Blur, Gaussian Blur (figure 31)
Enter 4 or the same value you entered for Maximum (figure 32).
This is the all-important step that produces transitions between what is sharpened and what is not.

9. Return to standard composite view by clicking on the top or RGB Channel in the Channels Pallet. Click on the Layers tab. Click on the image layer to make it active.

10. Load the selection.
Choose Selection, Load Selection (figure 33), Channel “copy” (figure 34). Your image should now have selection lines sometimes referred to as marching ants (figure 35). On the keyboard hold down Ctrl + H, this will hide the marching ants. Choose the Zoom Tool and right mouse click on the image to get actual pixels.

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Figure 27

11 . Choose Filter, Sharpen, Unsharp Mask
Make adjustments with threshold set to 0. Click OK.

After the filter is applied examine the image. If you are satisfied, you’re done (figure 36). If you’re not satisfied, type Ctrl + Z before doing anything else. Remember Ctrl + Z cancels the last action. Repeat the sharpening with new settings and apply.

That’s it, our basic Photoshop workflow.

Enjoy!

Michael and Tammy Rice

Figure 16 “After Cloning”

To sharpen an image using Unsharp Mask first set the image to actual pixels. As before select the zoom tool, right mouse click on the image and select actual pixel size. This view is needed to effectively adjust the sharpening on screen.

Adjust the sliders using the above values as starting points. When it comes to sharpening less is more. Over sharpening an image yields a very unnatural look.

Optional, Edge Sharpening

This basic method of sharpening works well on images that contain uniform detail throughout the image. Most images however are a mixture of detailed and non-detailed areas. Sharpening cannot be optimized for both types of areas. The threshold slider is an on off switch determining what is sharpened and what is not, but it is a crude tool offering no transitions between sharpened and unsharpened areas. Use of the threshold produces an unnatural look and should not be considered an option.

The solution is to sharpen through a mask, a mask that allows sharpening only the details, or edges between areas of different color and contrast. This is called an edge mask.

Although there are several methods for producing an edge mask, we use a method by Deke McClelland that we found quite some time ago in the Photoshop 4 for Windows 95 Bible by IDG Books. We have added a couple steps and automated most of the routine through use of an action. We continue to use it today, never having found a better method of producing an edge mask. The steps are as follows:

1. Duplicate one of the color channels
Choose the Channels palette and drag one of the color channels onto the new page icon at the bottom of the layers pallet. Choose the channel that has the most detail and the least noise (figure 24).

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