Adobe Photoshop CS5 for Photographers - Martin Evening [213]
1.
The four letter layers shown here are grouped together in a layer group. Layer A uses the Multiply blending mode; B uses the Overlay mode; C uses the Difference mode; and D uses the Screen blending mode. The default blending mode of the entire layer group is Pass Through. This means that the layers in the layer group blend with the layers below the same as they would if they were all in a normal layer stack.
2.
If you select ‘Layer D’ and double-click the layer to open the Layer Style dialog, you can alter the Advanced Blending options. The Knockout options (circled) allow you to ‘punch through’ the layers. A ‘Shallow’ knockout punches through the three layers below it to just above the layer or layer group immediately below. A ‘Deep’ knockout will make the Layer D punch through all the layers below it, straight down to the Background layer. In this example, Layer D uses the Deep Knockout blend and appears as it would if it were positioned directly above the Background layer.
3.
The default layer group blend mode is Pass Through. If you change the layer group blending mode to anything else, the layers within the group will blend with each other as before, but not interact with the layers underneath as they did in Pass Through mode. When the layer group blend mode is changed to Normal (shown circled), the group layers appear as they would if the Background and fern layer visibility were switched off.
The Photomerge layout options
Auto
The Auto layout works best in most cases and I suggest that you use Auto first to see what it does before considering any of the alternative layout options. Auto tends to fl atten the perspective and prevents the corners of a Photomerge from shooting outwards.
Perspective
The Perspective layout can produce good results when the processed photos are shot using a moderate wide-angle lens or longer, but can otherwise produce rather distorted, exaggerated composites.
Cylindrical
The Cylindrical layout ensures photos are aligned correctly on the horizontal axis. This is useful for keeping the horizon line straight when using Photomerge to process a series of photos that make up an elongated panorama.
Spherical
This can transform and warp the individual photos in both horizontal and vertical directions. This layout option is more adaptable when it comes to aligning tricky panoramic image sequences.
Collage
This positions the photos in a Photomerge layout without transforming the individual layers, but does rotate them to achieve the best fit.
Reposition
The Reposition layout simply repositions the photos in the Photomerge layout, without rotating them.
Creating panoramas with Photomerge
The Photomerge feature allows you to stitch individual photos together to build a panorama image and is now much simpler to work with. This is because since CS4, the Photomerge alignment and blending have been improved to the point where the interactive dialog is no longer necessary. In fact, in the majority of cases the ‘Auto’ layout option is all you need to get good-looking panoramas.
There are two ways to generate a Photomerge image. You can go to the File Automate menu in Photoshop and choose Photomerge… This opens the dialog shown in Step 2, where you can choose ‘Add Open Files’ and add these as the source images. Or, you can use Bridge to navigate to the photos you wish to process and open Photomerge via the Tools Photoshop submenu.
To get the best Photomerge results, you need to work from photographs where there is a significant overlap between each exposure. You should typically aim for at least a 25% overlap between each exposure and overlap the photos even more if you are using a wide-angle lens. For example, Photomerge is even optimized to work with fish eye lenses, providing Photoshop can access the lens profile data (see page 562), but if you do so, you should aim for maybe as much as a 70%