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Regardless of the type of sensor, the more pixels, the more information that is being captured. High resolution translates to digital photos with well-defined detail, great clarity, and an impression of high sharpness. Most digicams (see Figure 1.2) today capture images with a sensor that has at least 1 million pixels, also called one megapixel, and you can find professional SLR cameras with more than 10 megapixels for making ultra–high-resolution images. In practical terms, more megapixels translates to larger prints of high quality.
Figure 1.2: Compact digital cameras are available with image sensors ranging from 1 to 6 megapixels.
Courtesy Nikon Inc.
How Many Megapixels Do You Need?You can find compact cameras with resolution ranging from 1 megapixel to 8 megapixels. Generally speaking, you will want to look for a camera with the highest resolution available in your price range if you plan to make prints. How much resolution do you need r to make a beautiful inkjet photo? The following list provides a rule of thumb as to what you’ll need to make photographic quality prints of certain sizes, using the highest resolution and the lowest JPEG (named after the Joint Photographic Experts Group) compression capture mode for one of the better cameras in each resolution range. |
| Cameras with 1 megapixel sensors are suitable for very good 4 ??6~IN
prints and acceptable 5 ??7 prints.
Cameras with 2 megapixel sensors should allow you to make very good 5 ??7~IN prints and acceptable 8 ??10~IN prints from your best images. Cameras with 3 megapixel sensors generally produce images suitable for good 8 ??10~IN prints; the best 3 megapixel cameras can produce image quality suitable for making acceptable 11 ??14~IN prints. Cameras with 4 megapixel sensors should produce images that are suitable for fine 11 ??14~IN prints that you’ll be proud to show and share. With images from the best 4 megapixel cameras, you should be able to make very good 11 ??14~IN prints. Cameras with 5, 6, and 8 megapixel sensors are intended for those who want high quality in 13 ??19~IN prints and very close to photo quality in slightly larger prints.
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| Few photo printers can generate prints larger than 8.5 ??11~IN. Unless you plan to buy a larger format printer or often crop image files extensively (calling for greater enlargement of the smaller files), you should be very satisfied with a top-rated 4 megapixel compact digicam. If you plan to exhibit prints or sell images, or if you are extremely critical as to quality, you might want to consider models with even higher resolution. In SLR cameras, 5+ megapixel resolution has become the norm as discussed later. |
Before moving on to a review of the various types of digital cameras, it’s worth considering the various image capture modes that are mentioned in subsequent sections.
The most common image recording format used by digital cameras is JPEG. This popular format can be opened with virtually any imaging software in a computer. The JPEG format includes compression in order to reduce the size of the file to allow more images to be recorded on a memory card. When the file is opened in the computer, the data is uncompressed.
JPEG Format IssuesJPEG is a “lossy” format, meaning that it always causes a loss of information in the image. To produce a smaller file size, pixel values may be changed. This is most commonly done by breaking the image down into blocks, typically 16 ? 16 pixels, and then finding the most efficient way to describe the color within those blocks. That may involve changing pixel values so that the data can be described more efficiently. Higher amounts of compression applied to a JPEG image will result in a smaller file size, but it will also result in more information being lost in the process. That translates into a loss of detail in the image, as well as the creation of “artifacts.” These artifacts are visible as blocks of color in the image that don’t blend in well with the surrounding area. For example, you might see bright blocks of pixels in dark areas along a high-contrast edge in the image. Although the loss of detail and creation of artifacts can be a serious problem, they are usually not an issue if you use the minimal amount of JPEG compression. Therefore, I recommend that you avoid using settings that will cause the camera to apply a high level of compression. Stick with the camera’s top JPEG quality mode such as Ultra Fine or Best. |
Digital cameras offer several choices for recording JPEG images with options for Resolution (number of pixels) and for Quality (compression ratio.) You can choose to make a large, high-resolution image with low compression—often denoted in the camera’s menu as Large/Fine or Large/Super Fine—for optimal image quality. Or you can choose to make a lower-resolution image with a higher compression ratio for situations in which quality is not your primary concern. Cameras usually offer many combinations of resolution and compression, although some cameras simplify the process, offering only general image-quality options such as Best, Good, Normal, and E-mail. The Best option, for example, produces the highest resolution and lowest compression ratio.
Recommendation: Save Your JPEGs as TIFFsAfter downloading JPEG images to your computer, save them as TIFF (Tagged Image File Format), using the “Save As” feature in your image editing software. TIFF is an excellent choice for archiving image files as discussed in Chapter 9Save the TIFF files as your “master files.” If you need a small file of any image for Internet use, simply downsize a TIFF file for that purpose and save it under another file name as a JPEG. Retain your master file as you would save a negative in 35mm photography for subsequent use for other purposes. Granted, there will be occasions when you’ll select a low-resolution/higher-compression capture mode. You may decide to do so when you want certain photos to make only small prints, when you want photos only for Internet use, or when all your memory cards are almost full and have inadequate capacity for larger files. |
In addition to JPEG capture modes, digital SLR cameras, and some prosumer-level compact digicams, include a special capture mode referred to as RAW mode. When you select this option, the camera captures raw data from the sensor and saves it in a proprietary file format. The data is often compressed, using a lossless algorithm. After RAW images are downloaded from the camera to a computer, they must be converted to a standard image file format, such as TIFF, that is recognized by image-editing software. The conversion process requires special software that is included with the camera and also available from companies such as Adobe and PhaseOne.
Aside from slightly higher image quality than the best JPEG option, the primary advantage of the RAW capture mode is great latitude for correcting factors such as exposure and color rendition before converting the RAW data to an image format. Most of the RAW conversion programs (see Figure 1.3) offer features for adjusting brightness, white balance, and color saturation as well as other parameters, including sharpness and contrast.
Figure 1.3: RAW images must be converted to a conventional image format, such as TIFF, using special software. Most such software includes a wealth of image-enhancing capabilities; those intended for color and exposure correction are the most valuable. [F0103.tif]
Granted, images captured in JPEG or TIFF format—fully processed in-camera—can be adjusted with conventional image-editing software such as one of the Adobe Photoshop programs. However, any major corrections to exposure and color rendition are more effective when applied to raw data that has not yet been processed. Should you ever make an error that produces a RAW image that’s too dark, that’s too bright, or that has a strange color cast, it can probably be corrected quite effectively with the RAW converter software.
Recommendation: Use RAW Capture Mode for Large PrintsAlthough the best JPEG capture mode can produce very good to exceptional image quality (depending on the camera), a RAW image is superior in this respect. If your camera offers an option for capturing images in RAW format, use this feature when you want the finest possible image, such as when you intend to make large prints. A RAW image file maintains a higher level of quality than an image made in JPEG when the file size is increased in the RAW conversion software or later with image-editing software. Consequently, you will be able to make larger prints that are suitable for framing. |
RAW image capture offers another advantage: it records the image with 12-bit color depth instead of 8-bit used in other capture modes. Image files with the higher bit depth contain billions rather than millions of possible colors, so they exhibit a wider range of tones and colors for the best detail and smoothest gradations. When using the RAW image converter software to convert the image to a conventional TIFF format, you can choose to save images in 8-bit or 16-bit depth. I’ll discuss this topic in far more detail in Chapter 9.
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