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How to stitch panoramas

If you braved the cold weather and followed Andrea’s tutorial on the previous pages, you’ll now have a set of panoramic start shots that need to be stitched together. Photoshop is obviously capable of blending your images using Photomerge, but this process can be tedious and the results are often mixed. Because of this we’ve decided to ‘prepare’ our images in Photoshop, but we’ll stitch them together using Realviz’s Stitcher Express software (a copy of which is included on this issue’s cover disc). Stitcher Express has been purpose-made for this type of work, and makes it supremely easy to create fantastic-looking panoramas.

To ensure that your final pic is as smooth and convincing as possible, it’s vital that you pre-prepare your shots in Photoshop before you start the stitching process. As you’ll see, this involves making sure that colour balance, white balance and exposure are correct and, most importantly, that they match throughout. If you shot your sequence in RAW, you’ll also need to save the shots down as JPEGs before they can be imported into Stitcher Express.

With Express, the process of connecting and blending images is broken down into three easy steps. Once imported, your shots appear in the bottom Image Strip, and from here they need to be manually dragged into the main Work Space, then carefully aligned before auto-stitching takes place. The second stage – levelling the horizon and equalizing – is fully automated. Equalising refers to the smoothing out of any differences between the exposures of each segment. The final step is the rendering of the panorama. This process might sound a little confusing to start with, but our guide will ease any qualms.

1. Start Using icon tabs When it comes to stitching, there are three basic processes that can be quickly accessed through the icon tab menu at the top-left of the screen. These tabs act as a step-by-step procedure and help to guide you through the stitch, from the initial import to accessing the settings ready for the final export.

2. Correct the white balance To get started, open File1.jpg (on the CD) in Photoshop, and create a Curves Adjustment Layer. Click on the first of the three pipettes, Set Black Point, and click on a dark area of the image. Repeat this with the grey and white pipettes on corresponding areas of colour.

3. Correct the exposure Create a new Levels Adjustment Layer. Our shadow areas are a little dark, so move the mid-tone slider towards the black (left) to help lighten them. As with the Curves, use the Set Black, Grey and White Points pipettes to correct the images’ colour balance.

4. Checking values After correcting the first image, drag and drop the two Adjustment Layers on to the other images. Click on the first image, pick a white point and the value will appear in the Info window (RGB 255,255,255). Compare this with the other images.

5. Save as 8-bit JPEGs The exposures don’t need to be exact, but the closer you can get them to each other, the better the results when stitching. With images adjusted, save them as 8-bit JPEG files and open Stitcher Express. Under the Start Tab, click Load Images to import.

6. Stitch first images The imported images will appear in the Image Strip across the base of the interface. Click on the first image and drag it into the main work space. Next, click on the second image and align it with the first. Click the Stitch tab and the Stitch icon.

7. Force Stitch Due to large areas of the image with little or no detail – apart from the Houses of Parliament strip – you may find that Stitcher is unable to find any key points. If this is the case it will either prompt you to ‘Force Stitch’ or ‘Re-adjust’.

8. Rotate images The shortcut keys are extremely useful as you advance with your stitching. These include Alt-left-mouse to pan, Ctrl-alt-left-mouse to zoom, and Shift-right-mouse for rotating individual images. Knowing these will make your life much easier.

9. Render preparation With the Houses of Parliament rebuilt to their former glory, it’s time to export the image. Click on the third tab, Render, then click on the first two icons to adjust the horizons and equalise the images. Finally, click on the Render icon.

10. Rendering First click on the File Name option and choose a name and location to save the pan. In the Type drop-down menu select Snapshot, then JPG, click Auto Crop and maximise the size. Now click Render to export the final version of the image.

11. Export for Photoshop Images won’t always stitch together seamlessly, showing areas of ghosting or blurred overlaps. If this is the case, then choose PSD as the Export Type. This will create a Photoshop file with each component and blending mask on a different Layer.

12. Adjusting masks With the file open in Photoshop, make sure you have black and white in your colour palette, then choose a Layer with some ghosting and click on the Layer Mask. Use the Paint Brush at 50 per cent opacity to remove the ghosting.

13. Final step Final corrections To finish your panorama, check that all transitions between the images are smooth. If you need to remove any elements, use the Clone or Healing Brush and apply colour or exposure alterations with adjustment Layers. Finally, fl atten and save ready for printing.