Phần này giải thích một phương pháp quan điểm sửa chữa cơ bản bạn có thể sử dụng để sửa chữa một lựa chọn trong ảnh của bạn, sử dụng lưới Photoshop viện trợ. Thủ tục này giả định rằng hình ảnh của bạn được định hướng một cách chính xác (nghĩa là, nó không cần phải được luân chuyển). | 58 Adobe Photoshop CS2 Photographers Guide Figure Shot under incandescent illumination this photo has been partially corrected using Photoshop s Photo Filter capability. Lens Distortion Correction Here s something you cant readily do with your lenses but which Photoshop CS2 makes a snap correcting the most common varieties of distortion found in many types of optics. I introduced this tool earlier in this chapter. Now we re going to explore some of its capabilities. First I ll start off with a brief description of common lens distortions and why they need to be corrected. No Perfect Lens As you probably know there are no perfect lenses. Even the most sophisticated lens design developed for costly 8000 or more interchangeable lenses for digital and film SLRs are at best compromises of some sort. Lens designers depart from the theoretical perfect lens design to add features that photographers demand. Perhaps the lens is intended for low-light photography so the designer makes a trade-off here or there to allow a wider maximum aperture. Or the lens must be developed so it is physically shorter lighter or can be attached to an SLR camera without interfering with the mirror. Some lenses are designed so they can better work with ultraviolet illumination for scientific purposes or optimized for close-up photography. The most challenging lens design of all may be the zoom lens which with a continuous series of focal Chapter 2 Camera and Lens Effects in Photoshop 59 lengths is many lenses in one. There are lots of tricks optical magicians can work with including non-spherical lens surfaces special coatings and combinations of lens elements that move in strange ballets to improve your results. There are even lenses that jostle their elements in response to camera movement to stabilize the image when the shutter speed isn t fast enough. Because of all the compromises that must be made in building a lens various types of distortion and aberrations are unavoidable. .
