The Basics of Photo Stitching

Photos by Digon3 and jepoirrier.

Click on any image for a larger view.

Photo-Stitching, as the name suggests, is a procedure by which you can ‘stitch’ multiple photos together to get one large, comprehensive image. This is ideal for shooting landscapes and panoramas. The advantage of this technique is that even with a relatively inexpensive and low-megapixel camera, one can get images of sizes as large as even 20 MP, covering an angle of vision of upto 360 degrees. This article will cover the basics of shooting images for stitching, and how to actually stitch using relevant software.

Ideally, the images should be taken from the same point of view. To do this, using a tripod is highly recommended. Once the camera is set on the tripod, take multiple shots of the scene. After each shot, recompose the image by moving the camera either vertically or horizontally by not more than 70% of the previous frame. In other words, two consecutive photos must overlap around 30%. More overlap is better than not enough. Many of today’s digital cameras offer a ‘Stitch Assist’ (or similar) mode, wherein the camera guides one as to the amount of overlap between two successive images, and also names the series of images for stitching differently from other images. The most critical aspect of taking overlapping photos is to rotate the camera along its optical centre. Not doing this would result in parallax error and photos which are almost impossible to align straight. This can be ensured by using a ‘Panoramic Head’ on your tripod. But these heads are expensive, and an inexpensive trick I use is to hold the camera directly above my foot, and then rotate my body on the ball of my foot while keeping the camera still relative to my body.

This process is done on your computer, using software specially developed for this purpose. If you own a Canon camera, in all probability you already have Canon Photo-Stitch bundled in the accompanying software CD. Though basic, it does a good job stitching your images together. Other software for the purpose, which are more complicated and offer more control, are PTGui, PanaVue, PTAssember and PTMac.

Most of these programs have a simple one-click feature to stitch your photos together, which involves simply selecting the series of overlapping images and clicking a single button to stitch them together. But it always helps if one can scratch a bit deeper and control the stitching process to an extent. Software like PTAssember offers complete control over various parameters of photo stitching, which will be touched upon in the next paragraph.

Selecting Control Points - Control points are certain focal points in the overlapping region of an image pair, which will be used by the software to actually overlap and stitch the two images. Four control points are usually recommended, and they should be placed on solid features in the photograph, with fine detail, and must be spaced evenly across the overlapping region.

Selecting Camera Settings - Do not change the settings of the camera between shots. Exposure, white balance, focus, lighting, etc. should be identical in all shots.

Don't Use a Polarizing Filter - Remove your polarizer while shooting images for stitching, as the polarizer induces strong sky colour gradients, which may give an unnatural final image.

Avoid Changing Light & Moving Objects - If there is rapidly changing light, such as in a sunset or sunrise, its better to avoid attempting a stitch, as when photos with varying lighting are brought together, the final images tends to be quite unnatural. Similar is the case with a scene involving fast moving objects, like clouds on a windy day, people, etc.

Keep these tips in mind, go out with your camera and start shooting! You'll be pleasantly surprised how easy it is to get your own breathtaking landscapes!