RAW image format

RAW image file
File extension:.raf (Fuji)
.crw .cr2 (Canon)
.kdc .dcr (Kodak)
.mrw (Minolta)
.nef (Nikon)
.orf (Olympus)
.dng (Adobe)
.ptx .pef (Pentax)
.arw .srf (Sony)
.x3f (Sigma)
.erf (Epson)
.mos (Leaf)
.raw (Panasonic)
Type of format:Image file formats
A raw image file (sometimes written RAW image file ) contains minimally processed data from the image sensor of a digital camera or image scanner. Raw files are so named because they are not yet processed and ready to be used with a bitmap graphics editor or printed. Normally, the image will be processed by a raw converter in a wide-gamut internal colorspace where precise adjustments can be made before conversion to an RGB file format such as TIFF or JPEG for storage, printing, or further manipulation.

File contents

Providing a detailed and concise description of the content of raw files is highly problematic. There is no single raw format: they can be similar or radically different. Different manufacturers use their own proprietary and typically undocumented formats, which are collectively known as raw format. Often they also change the format from one model to the next. At least one manufacturer encrypts portions of the file. This industry-wide situation has engendered concern that in the future many very valuable raw photos may be rendered unopenable as operating systems and applications move forward and abandoned raw formats are dropped from new software. Ultimately any raw format's purpose is to faithfully record both 100% of exactly what the sensor "saw" (the data) and the conditions surrounding the recording of the image (the metadata).

Digital camera raw files contain the pixel data from a rectangular image sensor, the modern equivalent of traditional film, usually at 12 or 14 bits per sensor bucket. The sensor is almost invariably overlaid with a so-called Bayer filter, consisting of a mosaic of red, blue and green filters in alternating rows of RG and GB. Given that three colors fit uncomfortably in a rectangular grid, green was chosen to be doubly present, since the human eye is more sensitive to it. Green also often serves as the luminance channel, and as the dominant channel for in-camera black-and-white conversions. To retrieve an image from a raw file, this mosaic of data must be converted into a full RGB image. This is known as demosaicing, but is sometimes referred to as digital development.

One variation on the Bayer scheme is the RGBE sensor of the Sony DSC-F828, which experimented with exchanging the green in the RG rows with Emerald (cyan). Other sensors, such as the Foveon X3 sensor capture information directly in RGB form, having three pixel sensors in each location, one for each colour component; these camera RGB raw data still need to be processed to make an image file.

Flatbed and film scanner sensors are typically straight narrow RGB or RGBI (where "I" is infrared) strips that are swept across an image; other than that, the remainder of the discussion about raw files applies to them as well. (Some scanners do not allow the user access to the raw data at all, as a speed compromise. The raw data is processed very rapidly inside the scanner to select out the best part of the available dynamic range so only the result is passed to the computer for permanent storage.)

The contents of raw files include more information, and potentially higher quality, than the converted results, in which the rendering parameters are fixed, the color gamut is clipped, and there may be quantization and compression artifacts. Each pixel in a raw file has a greater bit-depth (compared to typical 8-bit renderings), and can thus store more subtle variations and range in color and detail. Hence, large transformations of the data, such as increasing the exposure of a dramatically under-exposed photo, result in less visible artifacts when done from raw data than when done from already rendered image files. Raw data leaves more scope for both corrections and artistic manipulations, without resulting in images with visible flaws such as posterization.

Benefits

Nearly all digital cameras can process the image from the sensor into a JPEG file using settings for white balance, color saturation, contrast, and sharpness that are either selected automatically or entered by the photographer before taking the picture. Cameras that support raw files save these settings in the file, but defer the processing. This results in an extra step for the photographer, so raw is normally only used when additional computer processing is intended. However, raw permits much greater control than JPEG for several reasons:
  • Finer control is easier for the settings when a mouse and keyboard are available to set them. For example, the white point can be set to any value, not just discrete values like "daylight" or "incandescent".
  • The settings can be previewed and tweaked to obtain the best quality image or desired effect. (With in-camera processing, the values must be set before the exposure). This is especially pertinent to the white balance setting since color casts can be difficult to correct after the conversion to RGB is done.
  • Camera raw files have 12 or 14 bits of intensity information, not the gamma-compressed 8 bits typically stored in processed TIFF and JPEG files; since the data are not yet rendered and clipped to a color space gamut, more precision may be available in highlights, shadows, and saturated colors.
  • The working color space can be set to whatever is desired.
  • Different demosaicing algorithms can be used, not just the one coded into the camera.

Drawbacks

Camera raw files are typically 2 – 6 times larger than JPEG files. Some raw formats do not use compression, some implement lossless data compression to reduce the size of the files without affecting image quality and others use lossy data compression where quantization and filtering is performed on the image data. While use of raw formats avoids the compression artifacts inherent in JPEG, fewer images can fit on a given memory card. It also takes longer for the camera to write raw images to the card, so fewer pictures can be taken in quick succession (affecting the ability to take, for example, a sports sequence).

There is still no widely accepted standard raw format. Adobe's Digital Negative (DNG) format has been put forward as a standard, but has not been adopted by major camera companies. Numerous different raw formats are currently in use and new raw formats keep being developed while others are orphaned.

Because of the lack of a standard raw format, more specialized software may be required to open raw files than for standardized formats like JPEG or TIFF. Software vendors are also having to frequently update their products to support the raw formats of the latest cameras.

The time taken in the image workflow is an important factor when choosing between raw and ready-to-use image formats.

Software support

Cameras that support raw files typically come with proprietary software for conversion of their raw format to TIFF or JPEG. Other conversion programs and plugins are available from vendors that have either licensed the technology from the camera manufacturer or reverse-engineered the particular raw format. A portable open source program, dcraw, supports most raw formats and can be made to run on operating systems not supported by most commercial software (such as Unix).

Raw file formats are proprietary, and differ greatly from one manufacturer to another, and sometimes between cameras made by one manufacturer. In 2004 Adobe Systems published the Digital Negative Specification (DNG), which is intended to be a unified raw format. Adobe Photoshop CS2 and CS3 contain extensive support of RAW as does Adobe Photoshop Lightroom. As of 2006, several camera manufacturers have started to announce support for DNG in newer camera models, including Leica, Samsung, Ricoh, Pentax (native camera support) and Hasselblad (export). The Leica Digital-Modul-R (DMR) was first to use DNG as its native format.

Microsoft's Digital Image 2006 was able to recognize and organize raw image formats such as .crw, .cr2, and .nef, which are file formats produced by Canon and Nikon, but that product was discontinued in 2007.[1] For the Windows platform, there is a free download available for Windows XP that integrates viewing and printing into other included photo tools, but it is not supported by Microsoft.[2]

In 2005, Apple Computer introduced several products which offered raw file support. In January, Apple released iPhoto 5, which offered basic support for viewing and editing raw files. In April, Apple introduced a new version of its operating system, Mac OS X v10.4, which added raw support directly to the operating system, as part of the ImageIO framework, which adds raw support automatically to the majority of Mac OS X applications both from Apple (such as Preview, Mac OS X's PDF and image viewing application and Aperture, a photo post-production software package for professionals) as well as all third party applications which make use of the ImageIO frameworks. Semi-regular updates to OS X generally include updated support for new RAW file formats introduced in the intervening months by camera makers.

There are many other "raw workflow applications" designed to provide efficient processing and post-processing of raw images, including Helicon Filter, Phase One's Capture One and Bibble Labs' Bibble Pro. Like Apple Aperture, Adobe Photoshop and Adobe Photoshop Lightroom, these programs provide sophisticated controls for processing the information stored in the Raw file and converting raw files to JPEG or TIFF. Picasa, a free image editing and cataloguing program from Google, can read and display many raw formats, but like iPhoto, Picasa provides only limited tools for processing the data in a raw file.

UFRaw is free software based on dcraw. It can be used as a GIMP plugin and is available for most operating systems.

RawShooter Essentials 2005/6 was free software developed by Pixmantec. In 2006 Adobe Systems Inc acquired the assets of Pixmantec ApS. RawShooter Essentials is no longer being updated (The last update added support for the Canon 5D and the Nikon D200). It could still be downloaded as a free product until Adobe's Photoshop Lightroom 1.0 was released in March 2007. The software was fully featured, including wide support for various raw formats, file priority sorting and batch processing. Light Crafts' LightZone photo editing software provides the ability to edit RAW natively. Most tools are "raw converters," but LightZone allows a user to edit RAW just as if it were TIFF or JPEG.

Processing

There is no single standard algorithm for converting data from a Bayer filter or Foveon sensor into RGB format; a number of different algorithms have been proposed, and some have been patented in the USA. Different programs may give slightly different results, better or worse subjectively, for any particular image.

Although the term "raw" describes files in the classical sense of "raw data" vs. "cooked data", raw files typically are slightly processed in the camera. In general, this processing is limited to algorithms that require direct access to the camera's hardware. This includes "long exposure noise reduction" (aka “dark frame subtraction”) and the mapping out of "hot" (too bright) or "dead" (too dim) pixels. Also information about standard processing parameters are stored in the file (so a Raw converter can generate the same JPEG file as the camera would create).

Some newer Raw formats also allow nonlinear quantization. This better allows to compress the raw data without visible degradation of the image by removing invisible and irrelevant information from the image. Although noise is discarded this has nothing to do with (visible) noise reduction.

References

1. ^ [1]
2. ^ [2]

See also

External links

  • Open RAW A working group of photographers and other people interested in advocating the open documentation of digital camera raw files
  • Adobe: Understanding Raw Files(PDF); Background on how camera sensors treat raw files
  • DCraw Raw Digital Photo Decoding in Linux Dave Coffin: software to process RAW data from various models of camera. Also shows all current cameras that support RAW. (supported models)
  • libopenraw, an ongoing effort to provide a free software implementation for camera RAW files decoding.
  • jrawio: An Open Source Java library for reading camera raw files from various digital camera models.
  • RAW Data 48 bit RAW data processing (High Dynamic Range Imaging)
  • Sample Olympus RAW file (15MB)
  • Pixmantec ApS Free download of RawShooter Essentials, a RAW batch converter.
  • Nikon Capture NX A Trial version of Nikon's raw processing software.
  • Adobe Lightroom
  • Raw Therapee (THe Experimental RAw Photo Editor) is a free RAW converter and digital photo processing software.
  • Light Crafts' LightZone Free Trial version of Light Crafts' Photo Editing Software that allows you to edit RAW natively.
  • RoboImport camera downloader software that performs batch conversion from RAW to Adobe DNG format
Photographers' views
A filename extension is a suffix to the name of a computer file applied to indicate its type. It is commonly used to infer information about what sort of data might be stored in the file.
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Fujifilm Holdings Corporation
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Public (TYO: 7751 , NYSE:  CAJ )
Founded Tokyo, Japan (August 10, 1937)
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Founded 1892
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Image file formats provide a standardized method of organizing and storing image data. This article deals with digital image formats used to store photographic and other image information.
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digital camera is an electronic device used to capture and store photographs digitally, instead of using photographic film like conventional cameras, or recording images in an analog format to magnetic tape like many video cameras.
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In computing, a scanner is a device that analyzes images, printed text, or handwriting, or an object (such as an ornament) and converts it to a digital image. Most scanners today are variations of the desktop (or flatbed) scanner.
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raster graphics editor is a computer program that allows users to paint and edit pictures interactively on the computer screen and save them in one of many popular “bitmap” or “raster” formats such as JPEG, PNG, GIF and TIFF.
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gamut, or color gamut (pronounced /ˈgæmət/), is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance,
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color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model.

In the most generic sense of the definition above, color spaces can be defined without the use of a color model.
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RGB color model is an additive model in which red, green, and blue (often used in additive light models) are combined in various ways to reproduce other colors. The name of the model and the abbreviation ‘RGB’ come from the three primary colors, red, green, and blue and
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Tagged Image File Format

File extension: .tiff, .tif
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JPEG

A photo of a flower compressed with successively more lossy compression ratios from left to right.
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encryption is the process of transforming information (referred to as plaintext) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key.
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pixel (short for picture element, using the common abbreviation "pix" for "pictures") is a single point in a graphic image. Each such information element is not really a dot, nor a square, but an abstract sample.
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Photographic film is a sheet of plastic (polyester, nitrocellulose or cellulose acetate) coated with an emulsion containing light-sensitive silver halide salts (bonded by gelatin) with variable crystal sizes that determine the sensitivity, contrast and resolution of the film.
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A Bayer filter mosaic is a color filter array (CFA) for arranging RGB color filters on a square grid of photosensors. The term derives from the name of its inventor, Dr. Bryce E.
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Black-and-white is a broad adjectival term used to describe a number of monochrome forms of visual arts. Most forms of visual technology start out in black and white, then slowly evolve into color as technology progresses.
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A demosaicing algorithm is a digital image process used to interpolate a complete image from the partial raw data received from the color-filtered image sensor (via a color filter array or CFA) internal to many digital cameras in form of a matrix of colored pixels.
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