
Digital photography is a form of photography that uses an array of light sensitive sensors to capture the image focused by the lens, as opposed to an exposure on light sensitive film. The captured image is then stored as a digital file ready for digital processing (colour correction, sizing, cropping, etc.), viewing or printing.
Until the advent of such technology, photographs were made by exposing light sensitive photographic film and used chemical photographic processing to develop and stabilize the image. By contrast, digital photographs can be displayed, printed, stored, manipulated, transmitted, and archived using digital and computer techniques, without chemical processing.
Digital photography is one of several forms of digital imaging. Digital images are also created by non-photographic equipment such as computer tomography scanners and radio telescopes. Digital images can also be made by scanning conventional photographic images.Sensors and storage
Image sensors read the intensity of light, and digital memory devices store the digital image information as RGB color space or as raw data.
There are two main types of sensors:
charge-coupled device (CCD) – photocharge is shifted to a central charge-to-voltage converter
CMOS sensors (“Active pixel sensor”)
Nearly all digital cameras use built-in and/or removable solid state flash memory. Digital tapeless camcorders that double as a digital still camera use flash memory, discs and internal hard drives. Certain 20th century digital cameras such as the Sony Mavica range used floppy disks and mini-CDs.
Multifunctionality and connectivity
Except for some linear array type of cameras at the highest-end and simple web cams at the lowest-end, a digital memory device (usually a memory card; floppy disks and CD-RWs are less common) is used for storing images, which may be transferred to a computer later.
Digital cameras can take pictures, and may also record sound and video. Some can be used as webcams, some can use the PictBridge standard to
anything goes diet connect to a printer without using a computer, and some can display pictures directly on a television set. Similarly, many camcorders can take still photographs, and store them on videotape or on flash memorycards with the same functionality as digital cameras.
Performance metrics
The quality of a digital image is a composite of various factors, many of which are similar to those of film cameras. Pixel count (typically listed in megapixels, millions of pixels) is only one of the major factors, though it is the most heavily marketed figure of merit. Digital camera manufacturers advertise this
sell house fast figure because consumers can use it to easily compare camera capabilities. It is not, however, the major factor in evaluating a digital camera for most applications. The processing system inside the camera that turns the raw data into a color-balanced and pleasing photograph is usually more critical, which is why some 4+ megapixel cameras perform better than higher-end cameras.
Resolution in pixels is not the only measure of image quality. A larger sensor with
we buy any house the same number of pixels generally produces a better image than a smaller one. One of the most important differences is an improvement in image noise. This is one of the advantages of digital SLR cameras, which have larger sensors than simpler cameras of the same resolution.
Lens quality: resolution, distortion, dispersion (see Lens (optics))
Capture medium: CMOS, CCD, negative film, reversal film etc.
Capture format: pixel count, digital file type (RAW, TIFF, JPEG), film format (135 film, 120 film, 5×4, 10×8).
Processing: digital and / or chemical processing of ‘negative’ and ‘print’.
Pixel counts
The number of pixels n for a given maximum resolution (w horizontal pixels by h vertical pixels) is the product n = w × h. This yields e. g. 1.92 megapixels (1,920,000 pixels) for an image of 1600 × 1200. The majority of compact as well as some DSLR digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3.[1] According to Digital Photography Review, the 4:3 ratio is because “computer monitors are 4:3 ratio, old CCD’s always had a 4:3 ratio, and thus digital cameras inherited this aspect ratio.”[1]
The pixel count quoted by manufacturers can be misleading as it may not be the number of full-colour pixels. For cameras using single-chip image sensors the number claimed is the total number of single-colour-sensitive photosensors, whether they have different locations in the plane, as with the Bayer sensor, or in stacks of three co-located photosensors as in the Foveon X3 sensor. However, the images have different numbers of RGB pixels: Bayer-sensor cameras produce as many RGB pixels as photosensors via demosaicing (interpolation), while Foveon sensors produce uninterpolated image files with one-third as many RGB pixels as photosensors. It is difficult to compare the resolutions based on the megapixel ratings of these two types of sensors, and therefore sometimes subject of dispute.[2]
The relative increase in detail resulting from an increase in resolution is better compared by looking at the number of pixels across (or down) the picture, rather than the total number of pixels in the picture area. For example, a sensor of 2560 × 1600 sensor elements is described as “4 megapixels” (2560 × 1600 = 4,096,000). Increasing to 3200 × 2048 increases the pixels in the picture to 6,553,600 (6.5 megapixels), a factor of 1.6, but the pixels per cm in the picture (at the same image size) increases by only 1.25 times. A measure of the comparative increase in linear resolution is the square root of the increase in area resolution, i.e., megapixels in the entire image.
Dynamic range
Practical imaging systems, digital and film, have a limited “dynamic range”: the range of luminosity that can be reproduced accurately. Highlights of the subject that are too bright are rendered as white, with no detail; shadows that are too dark are rendered as black. The loss of detail is not abrupt with film, or in dark shadows with digital sensors: some detail is retained as brightness moves out of the dynamic range. “Highlight burn-out” of digital sensors, however, can be abrupt, and highlight detail may be lost. And as the sensor elements for different colors saturate in turn, there can be gross hue or saturation shift in burnt-out highlights.
Some digital cameras can show these blown highlights in the image review, allowing the photographer to re-shoot the picture with a modified exposure. Others compensate for the total contrast of a scene by selectively exposing darker pixels longer. A third technique is used by Fujifilm in its FinePix S3 Pro digital SLR. The image sensor contains additional photodiodes of lower sensitivity than the main ones; these retain detail in parts of the image too bright for the main sensor.
High dynamic range imaging (HDR) addresses this problem by increasing the dynamic range of images by either
increasing the dynamic range of the image sensor or
by using exposure bracketing and post-processing the separate images to create a single image with a higher dynamic range.
HDR images curtail burn-outs and black-outs.
Digital photography is a form of photography that uses an array of light sensitive sensors to capture the image focused by the lens, as opposed to an exposure on light sensitive film. The captured image is then stored as a digital file ready for digital processing (colour correction, sizing, cropping, etc.), viewing or printing.Until the advent of such technology, photographs were made by exposing light sensitive photographic film and used chemical photographic processing to develop and stabilize the image. By contrast, digital photographs can be displayed, printed, stored, manipulated, transmitted, and archived using digital and computer techniques, without chemical processing.Digital photography is one of several forms of digital imaging. Digital images are also created by non-photographic equipment such as computer tomography scanners and radio telescopes. Digital images can also be made by scanning conventional photographic images.Sensors and storage
Image sensors read the intensity of light, and digital memory devices store the digital image information as RGB color space or as raw data.There are two main types of sensors:charge-coupled device (CCD) – photocharge is shifted to a central charge-to-voltage converterCMOS sensors (“Active pixel sensor”)Nearly all digital cameras use built-in and/or removable solid state flash memory. Digital tapeless camcorders that double as a digital still camera use flash memory, discs and internal hard drives. Certain 20th century digital cameras such as the Sony Mavica range used floppy disks and mini-CDs.Multifunctionality and connectivity
Except for some linear array type of cameras at the highest-end and simple web cams at the lowest-end, a digital memory device (usually a memory card; floppy disks and CD-RWs are less common) is used for storing images, which may be transferred to a computer later.Digital cameras can take pictures, and may also record sound and video. Some can be used as webcams, some can use the PictBridge standard to connect to a printer without using a computer, and some can display pictures directly on a television set. Similarly, many camcorders can take still photographs, and store them on videotape or on flash memorycards with the same functionality as digital cameras.Performance metrics
The quality of a digital image is a composite of various factors, many of which are similar to those of film cameras. Pixel count (typically listed in megapixels, millions of pixels) is only one of the major factors, though it is the most heavily marketed figure of merit. Digital camera manufacturers advertise this figure because consumers can use it to easily compare camera capabilities. It is not, however, the major factor in evaluating a digital camera for most applications. The processing system inside the camera that turns the raw data into a color-balanced and pleasing photograph is usually more critical, which is why some 4+ megapixel cameras perform better than higher-end cameras.Resolution in pixels is not the only measure of image quality. A larger sensor with the same number of pixels generally produces a better image than a smaller one. One of the most important differences is an improvement in image noise. This is one of the advantages of digital SLR cameras, which have larger sensors than simpler cameras of the same resolution.Lens quality: resolution, distortion, dispersion (see Lens (optics))Capture medium: CMOS, CCD, negative film, reversal film etc.Capture format: pixel count, digital file type (RAW, TIFF, JPEG), film format (135 film, 120 film, 5×4, 10×8).Processing: digital and / or chemical processing of ‘negative’ and ‘print’.Pixel countsThe number of pixels n for a given maximum resolution (w horizontal pixels by h vertical pixels) is the product n = w × h. This yields e. g. 1.92 megapixels (1,920,000 pixels) for an image of 1600 × 1200. The majority of compact as well as some DSLR digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3.[1] According to Digital Photography Review, the 4:3 ratio is because “computer monitors are 4:3 ratio, old CCD’s always had a 4:3 ratio, and thus digital cameras inherited this aspect ratio.”[1]The pixel count quoted by manufacturers can be misleading as it may not be the number of full-colour pixels. For cameras using single-chip image sensors the number claimed is the total number of single-colour-sensitive photosensors, whether they have different locations in the plane, as with the Bayer sensor, or in stacks of three co-located photosensors as in the Foveon X3 sensor. However, the images have different numbers of RGB pixels: Bayer-sensor cameras produce as many RGB pixels as photosensors via demosaicing (interpolation), while Foveon sensors produce uninterpolated image files with one-third as many RGB pixels as photosensors. It is difficult to compare the resolutions based on the megapixel ratings of these two types of sensors, and therefore sometimes subject of dispute.[2]The relative increase in detail resulting from an increase in resolution is better compared by looking at the number of pixels across (or down) the picture, rather than the total number of pixels in the picture area. For example, a sensor of 2560 × 1600 sensor elements is described as “4 megapixels” (2560 × 1600 = 4,096,000). Increasing to 3200 × 2048 increases the pixels in the picture to 6,553,600 (6.5 megapixels), a factor of 1.6, but the pixels per cm in the picture (at the same image size) increases by only 1.25 times. A measure of the comparative increase in linear resolution is the square root of the increase in area resolution, i.e., megapixels in the entire image.Dynamic rangePractical imaging systems, digital and film, have a limited “dynamic range”: the range of luminosity that can be reproduced accurately. Highlights of the subject that are too bright are rendered as white, with no detail; shadows that are too dark are rendered as black. The loss of detail is not abrupt with film, or in dark shadows with digital sensors: some detail is retained as brightness moves out of the dynamic range. “Highlight burn-out” of digital sensors, however, can be abrupt, and highlight detail may be lost. And as the sensor elements for different colors saturate in turn, there can be gross hue or saturation shift in burnt-out highlights.Some digital cameras can show these blown highlights in the image review, allowing the photographer to re-shoot the picture with a modified exposure. Others compensate for the total contrast of a scene by selectively exposing darker pixels longer. A third technique is used by Fujifilm in its FinePix S3 Pro digital SLR. The image sensor contains additional photodiodes of lower sensitivity than the main ones; these retain detail in parts of the image too bright for the main sensor.High dynamic range imaging (HDR) addresses this problem by increasing the dynamic range of images by eitherincreasing the dynamic range of the image sensor orby using exposure bracketing and post-processing the separate images to create a single image with a higher dynamic range.HDR images curtail burn-outs and black-outs.