Clipping (photography)
Encyclopedia
Digital imaging
Digital imaging or digital image acquisition is the creation of digital images, typically from a physical scene. The term is often assumed to imply or include the processing, compression, storage, printing, and display of such images...
or processing
Digital image processing
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
an image where the intensity in a certain area falls outside the minimum and maximum intensity which can be represented. It is an instance of signal clipping
Clipping (signal processing)
Clipping is a form of distortion that limits a signal once it exceeds a threshold. Clipping may occur when a signal is recorded by a sensor that has constraints on the range of data it can measure, it can occur when a signal is digitized, or it can occur any other time an analog or digital signal...
in the image domain. The clipped area of the image will typically appear as a uniform area of the minimum or maximum brightness, losing any image detail. The amount by which values were clipped, and the extent of the clipped area, affect the degree to which the clipping is visually noticeable or undesirable in the resulting image.
In a color image, clipping may occur in any of the image's color channels separately.
Clipping can occur at many different stages. It may occur in the image sensor
Image sensor
An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices...
when initially capturing the image using a digital camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
or scanner
Image scanner
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...
. It may occur due to internal image processing
Digital image processing
Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...
or color space
Color space
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...
conversion in the camera or scanner. It may also result from later image processing using image editing
Image editing
Image editing encompasses the processes of altering images, whether they be digital photographs, traditional analog photographs, or illustrations. Traditional analog image editing is known as photo retouching, using tools such as an airbrush to modify photographs, or editing illustrations with any...
software. Clipping that is due to internal image processing in a digital camera may often be partially or fully recovered if the raw sensor data is available, such as when saving to a raw image format
RAW image format
A camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor...
.
Clipping due to overexposure
Clipping can often occur in image highlights as a result of an incorrect exposureExposure (photography)
In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
when initially photographing or scanning to a digital image. Increasing an exposure increases the amount of light collected or the sensitivity of the sensor, and increasing it too far will cause the lightest areas, such as the sky, or light sources, to clip.
Bright areas due to overexposure are sometimes called blown-out highlights or flared highlights. In extreme cases, the clipped area may appear to have a noticeable border between the clipped and non-clipped area. The clipped area will typically be completely white, though in the case that only one color channel has clipped, it may represent itself as an area of distorted color, such as an area of sky that is greener or yellower than it should be.
A similar effect of blown-out highlights also exists in analog photography
Analog photography
Analog photography is a commonly used term for photography that uses a progressively changing recording medium, which may be either chemical process based or electronic ....
, though in that case it is not referred to as "clipping", and the "blown-out" area often curves off gently to its maximum brightness rather than being cut off abruptly as in clipping. This causes blown-out highlights to appear differently in analog and digital photography, with the smooth edges in analog photography regarded as more pleasant to some.
In some cases, a small amount of clipping may be tolerable, especially when the clipped area is in the background of the image rather than part of the main subject, or is only a very small area such as where a light, or the sun, is reflected in a shiny object.
Out-of-gamut clipping
Clipping in some color channels may occur when an image is rendered to a different color spaceColor space
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...
, when the image contains colors that fall outside the target color space. Such colors are referred to as out-of-gamut.
This form of clipping may be avoided by performing the color space conversion using a different rendering intent. However, this can sometimes result in a lower overall color saturation, leading to duller colors. The desire for bright, saturated colors may, in some cases, be more important than avoiding clipping in single channels due to out-of-gamut colors.
Digital video
Clipping may occur in digital videoDigital video
Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
, just as in digital still photography.
Just as with digital still photography, an intensity value that is outside the allowed range of values in any one channel causes clipping.
See also
- Exposure (photography)Exposure (photography)In photography, exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value and scene luminance over a specified area.In photographic jargon, an exposure...
- High dynamic rangeHigh dynamic rangeHigh dynamic range is a term generally used for media applications such as digital imaging and digital audio production...
- Graduated neutral density filterGraduated neutral density filterA graduated neutral density filter, also known as a graduated ND filter, split neutral density filter, or just a graduated filter, is an optical filter that has a variable light transmission. Typically half of the filter is of neutral density which transitions, either abruptly or gradually, into...