As technology continues to expand, so does the vocabulary describing it. To help you stay on top of the field, we’ve decided to squeeze in an occasional glossary page of industry terms for a quick refresher or maybe even as a first-time explanation. For the first Fundamentals entry, we’ve zoomed in on digital camera terms.
Aberration Optical imperfections within a lens that cause distortions in the image. Most aberrations can be minimized through the use of corrective elements within a lens design.
APO (Apochromatic) Lenses that use internal elements to bring all colors of the visible spectrum to a common point of focus, creating a sharp image, are referred to as APO lenses.
Bit-Depth Also referred to as color depth, bit-depth determines the maximum number of colors that can be represented at a time. Camera sensors typically have 12-bit-per-channel color (red, green and blue) for a 36-bit image (which JPEG compression reduces to 8 bits per channel). Although more bit-depth is preferable, there are diminishing returns beyond 8 bits per channel. Image file sizes increase dramatically, and the increase in image quality may not be worth it for many photographers.
CCD (Charge-Coupled Device) An electronic image sensor for digital cameras. Most digital cameras are built around CCD sensors.
CMOS (Complementary Metal Oxide Semiconductor) A sensor technology that encompasses all required camera circuits on a single chip. Because a CMOS sensor requires less power and generates less heat than a CCD-based system, many large, high-resolution digital cameras use CMOS technology.
Compression The process of encoding files through an algorithm, which decreases the size for storage or transmission over the Internet. There are two types of compression: lossy and lossless. Lossy compression (JPEG is an example) results in a visible degradation in image quality because some image data is lost in the compression process. Lossless compression (like LZW compression) preserves all image data.
Digital Zoom A simulated zoom effect that enlarges the image on a portion of the image sensor. Because fewer pixels are used to capture the image, you end up with a significantly lower-resolution final image.
Effective Pixels Pixels on the sensor actually used to capture an image. Often, not all the pixels on a sensor can be used because: 1) some pixels on the surrounding edges of a sensor are masked off to determine a black point; or 2) some cameras, especially compact ones, have lenses that are unable to cover the entire sensor area.
Interpolation (or Resampling) Artificially increasing or decreasing the number of pixels in an image through the use of an algorithm. Some cameras increase the number of pixels automatically to compensate for digital zoom.
JPEG (Joint Pictures Expert Group) A common algorithm for the compression of image files. JPEG compression can vary from nearly lossless to highly glossy. Because JPEG is a standard, JPEG image files can be read by all image-processing software.
LD, ED and UD Glass (Low-Dispersion, Extra-Low-Dispersion and Ultra-Low-Dispersion Glass) All these terms refer to a glass type used in lenses. They denote rare or specially formulated glass that corrects the path of light rays as they pass through the lens, making all colors in the color spectrum focus at the same point.
Megapixel (one million pixels) The number of photodiodes (also known as photosites or pixels) on an image sensor is expressed in megapixels, which in turn is the resolution of the device (a camera, scanner, etc.). Most sensors have one photodiode for each pixel in an image. For example, a 5-megapixel camera has five million photodiodes.
Noise Image artifacts caused by statistical variations with color that manifest themselves as grain on an image. Excessive noise usually results in an objectionable-looking image. Smaller image sensors with physically smaller photodiodes are more subject to noise than sensors with larger photodiodes.
RAW An image-capture option containing the maximum information available from a sensor. The format is offered by many high-end compact digital cameras as well as D-SLRs. Each camera company has its own RAW format and corresponding software to support the format.
Resolution Camera resolution expressed in the number of photodiodes (megapixels) on the image sensor. More megapixels equals higher resolution. It’s important to note that many factors go into image quality, and resolution is only one of them. If you have a poor-quality lens on a high-resolution camera, you’ll get a high-resolution image of poor quality. Higher-resolution image files can be enlarged with less interpolation than lower-resolution image files.
TIFF (Tagged Image File Format) A standard image file format for bitmapped graphics. TIFF files are uncompressed and, therefore, very large compared to compressed formats. Because TIFF is a standard, TIFF image files can be read by all image-processing software.