Photography Glossary
A
- Acutance
- Refers to how noticeable the transition is from one luminosity to another across an edge.
- See Also: Sharpness | Contrast
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- APS-C
- APS-Crop
- Refers a digital camera sensor similar in size to a frame of APS film (typically around 22mm x 15mm in size) when used in a standard 35mm format camera body.
- APS-C is a “cropped” sensor since it only records the center portion of the imaging circle intended for a full-frame of 35mm film (36mm x 24mm).
- See Also: Crop Factor
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- Aspect Ratio
- Refers to the relationship of one dimension to another for a rectangle or square.
- Aspect ratios can typically be written as either 1.5 or 2:3. Both are different ways of displaying the same information.
- Examples:
- 1.5 – Indicates the longest dimension is 1.5 times longer than the short dimension (i.e. 6 is 1.5 times greater than 4 for a 4x6" print thus it has a aspect ratio of 1.5).
- 2:3 – (pronounced “two to three”) For every two units along one dimension, there are three units along the other dimension.
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B
- Bitmap
- A type of image consisting of pixels laid out in a mosaic pattern.
- Also known as a raster image.
- See Also: Image Formats: Bitmap
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C
- Contrast
- The visually perceivable difference between two different values of luminance or color.
- Increasing contrast for an image effectively reduces its dynamic range (DR) but can give it a more pleasing appearance by increasing the noticeable different between tones. Reducing the contrast has the opposite effect.
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- Global Contrast: Adjusts contrast equally to all portions of an image.
- Local Contrast: A means of adjusting contrast by comparing elements within the image to each other. Typically achieved with an Unsharp Mask tool using a large radius and small percentage of strength.
- Micro Contrast: Determines a lens ability to distinguish between small variations in luminosity. Effects how much small detail the lens can appear to resolve.
- See Also: Sharpness
- Related Article: Understanding Lens Contrast
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- Crop Factor
- Describes how much of a crop a sensor has in relation to its full-frame equivalent. Always described as how many times larger the full-frame is in relation to the cropped sensor.
- An APS-C sensor with a crop factor of 1.6 indicates it is 60% of the size of a frame of 35mm film.
- Crop factors are used to calculate the full-frame Field of View (FOV) equivalent the cropped sensor will have with any given lens. This is done by multiplying the lens focal-length by the crop factor. For example, a 1.6 crop-factor will give a 50mm lens the same FOV as a 80mm lens on a full-frame camera.
- See Also: mm-e
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D
- DPI
- Acronym: Dots Per Inch
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- See PPI. When referring to non-printed images DPI is often used although PPI would be more accurate.
- A term used to measure how many dots a printer will lay out on paper per inch for its screening pattern. Often used to describe a printers resolution. At proper viewing distances these dots can be dense enough to give the appearance of a continuos-tone print.
- See Also: PPI
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- Dynamic Range
- Acronym: DR
- The range of light intensity in a scene from the brightest area in the scene to the darkest shadows. Measured in stops of light.
- The dynamic range rating of a sensor, film or print paper indicates how broad of a range of light that the sensor/film/paper can record.
- See Also: Contrast
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- DX Format
- Nikon’s marketing term for their 23.6mm x 15.8mm APS-C sensors.
- DX cameras have a 1.5 crop-factor.
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E
- EXIF
- Acronym: EXchangeable Image File
- A metadata standard created by JEIDA to store valuable information about an image including capture information, camera info, capture time. EXIF data is stored within the header of an image file.
- Related Site: EXIF.org
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F
- Full Frame
- Indicates a imaging sensor equivalent in size to the film used for that particular format of camera.
- See Also: APS-C
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- Field of View
- How many degrees horizontally of a scene a lens can capture.
- Longer lenses have more narrow FOVs, while wider lenses have a broader FOV. A lens with a similar FOV as the human eye of about 45° is considered a “normal” lens.
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L
- lpm
- Lines Per Millimeter
- A means of measuring optical resolution. A lpm value describes how many lines can be found within a millimeter. The higher the lmp, the higher the resolution.
- Similar to this is Line Pairs per Millimeter (lppm). Not to be confused with lpm, lppm requires two lines for each value; one white and one black. One school of thought states in order to have a black line, there must be a white line to distinguish it from the other black lines. It makes sense but not everyone is that particular and so lpm is more typically used.
- 5 lppm is the equivalent of 10 lpm.
- See Also: Resolution
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M
- Medium
- The basis of an art or craft (i.e. Oil Painting, Film, Pen & Ink, etc).
- Also refers to the type of capture device (film/sensor).
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- Megapixel
- Written as “megapixel,” “MP,” or “mp”
- The total number of pixels in an image. Expressed in Millions of pixels.
- To calculate the megapixel value of a camera or image multiply the pixel dimensions against each other. Example: 3076 * 2052 = 6,311,952 or 6.3MP
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- mm-e
- 35 Millimeter Equivalent
- Denotes the 35mm format equivalent focal length of a lens used on a camera with a cropped sensor or non-35mm format camera.
- APS-C Example: A 50mm lens used on a APS-C camera with a 1.5 crop-factor would produce a field of view that is equivalent to a 75mm lens (1.5*50) on a full-frame 35mm camera. In this example, the 50mm lens would be described as having a 75mm-e.
- Non-35mm Format: A camera using the Four-Thirds format has a sensor half the size of a 35mm format camera. This means a lens of 50mm designed for Four-Thirds system would have a 100mm-e. Similarly, an 80mm lens for 645 medium format would be 48mm-e (80 * 0.6 = 48).
- See Also: APS-C | Crop Factor | FOV | Full Frame
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P
- Pixel
- Derived from the term “picture element,” a pixel is the smallest visual element of a digital image. These square-shaped elements of varying luminosity and color values are combined to create a raster image.
- Pixels are simply bits of information and have no physical size.
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- Post
- The process of developing and editing an image after it has been captured.
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- PPI
- Acronym: Pixels Per Inch
- A means to translate an images pixel resolution into a physical dimension. PPI states how many pixels will span the length of an inch. PPI values are stored within the metadata and can be changed arbitrarily with no effect on the actual pixel resolution of an image.
- Often mistakenly referred to as DPI.
- To calculate pixel resolution into physical dimension using PPI:
Pixel Resolution Dimension / PPI = Inches - Example: An image at a resolution of 3076 x 2052 @ 300 ppi will equal 10.253 by 6.84 inches.
- See Also: DPI | Resolution
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R
- Resolved Detail
- The amount of detail that can be resolved optically within an image.
- See Also: Resolution | Contrast | Sharpness
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- Resolution
- Analog/Optical Resolution: The amount of detail film, print paper or lens optics can resolve. Expressed in Lines per Millimeter (lpm).
- Pixel Resolution: The number of pixels that an image contains. Expressed as number of pixels wide by number of pixels high. Example: 3076 x 2052
- Print Resolution: similar to pixel resolution but measured in Dots Per Inch (dpi).
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Note: There can be some confusion as to what resolution is. For analog systems it refers to resolved detail, or, the contrast between the smallest lines (measured in lpm). It’s quite subjective and not an exact science as many variables can effect it.
For digital however, the resolution of an image refers specifically to the pixel dimensions. Even if one digital camera image with 1000 x 1000 pixels shows more detail than another digital image of 1000 x 1000 pixels, they have still the same pixel resolution although each has captured a different optical resolution. Definition 1 can be used for optics on a digital camera, but as soon as the image is captured, the definition generally switches to definition 2 unless specified otherwise.
When discussing resolution, one should state clearly if they are talking about optical or pixel resolution in order to avoid confusion.
- See Also: Megapixel | Resolved Detail | Sharpness
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S
U
- USM
- Acronym: UnSharp Mask
- A tool used in editing software for increasing edge contrast in an image in order to increase its apparent sharpness.
- The current digital form of USM stems from traditional film-based printmaking. A negative was duplicated slightly out of focus then mashed together with the original and placed in an enlarger. The exposure time for the paper is then doubled to compensate for the added density. The resulting effect further lightens light edges and darkens dark edges. This increases the contrast of the edges thus increasing the apparent sharpness of a print. In short, the unsharp negative was used to create a mask used for sharpening the original image.
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V
- Vector
- An image format derived from geometrical objects described by mathematics. Unlike raster images, vectors are infinitely scaleable.
- Similar to PostScript
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