Okay, I don't understand RAW... 

 

It's supposed to be a format, right? Why does every single camera require separate support?

A DNG file always contains data for one main image, plus metadata, and optionally contains at least one JPEG preview.[2] It normally has the extension "dng" or "DNG".

DNG conforms to TIFF/EP and is structured according to TIFF. DNG supports various formats of metadata, (including Exif metadata, XMP metadata, IPTC metadata), and specifies a set of mandated metadata.[28]

DNG is both a raw image format and a format that supports "non-raw", or partly processed, images.[2] The latter (non-raw) format is known as "Linear DNG".[31] Linear DNG is still scene-referred and can still benefit from many of the operations typically performed by a raw converter, such as white balance, the application of a camera color profile, HDR compositing, etc. All images that can be supported as raw images can also be supported as Linear DNG. Images from the Foveon X3 sensor or similar, hence especially Sigma cameras, can only be supported as Linear DNG.

DNG can contain raw image data from sensors with various configurations of color filter array (CFA). These include: conventional Bayer filters, using 3 colors and rectangular pixels; 4 color CFAs, for example the RGBE filter used in the Sony DSC-F828; rectangular (non-square) pixels, for example as used in the Nikon D1X; and offset sensors (for example with octagonal pixels) such as Super CCD sensors of various types, as used in various Fujifilm cameras. (Or combinations of these if necessary). DNG specifies metadata describing these individual parameters; this is one significant extension to TIFF/EP.

When used in a CinemaDNG movie clip, each frame is encoded using the above DNG image format. The clip's image stream can then be stored in one of two formats: either as video essence using frame-based wrapping in an MXF file, or as a sequence of DNG files in a specified file directory.

Benefits

Nearly all digital cameras can process the image from the sensor into a JPEG file using settings for white balance, colour saturation, contrast, and sharpness that are either selected automatically or entered by the photographer before taking the picture. Cameras that produce 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 has numerous advantages over JPEG such as:

Higher image quality. Because all the calculations (such as applying gamma correction, demosaicing, white balance, brightness, contrast, etc...) used to generate pixel values (in RGB format for most images) are performed in one step on the base data, the resultant pixel values will be more accurate and exhibit less posterization. Bypassing of undesired steps in the camera's processing, including sharpening and noise reduction JPEG images are typically saved using a lossy compression format (though a lossless JPEG compression is now available). Raw formats typically use lossless compression or high quality lossy compression. Finer control. Raw conversion software allows users to manipulate more parameters (such as lightness, white balance, hue, saturation, etc...) and do so with greater variability. For example, the white point can be set to any value, not just discrete preset values like "daylight" or "incandescent". As well, the user can typically see a preview while adjusting these parameters. Camera raw files have 12 or 14 bits of intensity information, not the gamma-compressed 8 bits stored in JPEG files (and typically stored in processed TIFF files); since the data is not yet rendered and clipped to a colour space gamut, more precision may be available in highlights, shadows, and saturated colours. The colour space can be set to whatever is desired. Different demosaicing algorithms can be used, not just the one coded into the camera. The contents of raw files include more information, and potentially higher quality, than the converted results, in which the rendering parameters are fixed, the colour gamut is clipped, and there may be quantization and compression artifacts. Large transformations of the data, such as increasing the exposure of a dramatically under-exposed photo, result in fewer visible artifacts when done from raw data than when done from already rendered image files. Raw data leave more scope for both corrections and artistic manipulations, without resulting in images with visible flaws such as posterization. All the changes made on a RAW image file are non-destructive; that is, only the metadata that controls the rendering is changed to make different output versions, leaving the original data unchanged. To some extent, RAW photography eliminates the need to use the HDRI technique, allowing a much better control over the mapping of the scene intensity range into the output tonal range, compared to the process of automatically mapping to JPEG or other 8-bit representation.

Drawbacks Camera raw file size are typically 2-6 times larger than JPEG file size.[12] While use of raw formats avoids the compression artifacts inherent in JPEG, fewer images can fit on a given memory card. However, the large sizes and low prices of modern memory cards mitigate this. Most raw formats implement lossless data compression to reduce the size of the files without affecting image quality. But some others use lossy data compression where quantization and filtering is performed on the image data.[13][14] Several recent Nikon cameras let photographers choose between no compression, lossless compression or lossy compression for their raw images. The standard raw image format (ISO 12234-2, TIFF/EP) is not widely accepted. DNG, the potential candidate for a new standard format, has not been adopted by many major camera companies. (See "Standardization" section). Numerous different raw formats are currently in use and new raw formats keep appearing, while others are abandoned.[15] Because of the lack of widespread adoption of a standard raw format, more specialized software may be required to open raw files than for standardized formats like JPEG or TIFF. Software developers have to frequently update their products to support the raw formats of the latest cameras but open source implementations like dcraw make it easier. The time taken in the image workflow is an important factor when choosing between raw and ready-to-use image formats. With modern photo editing software the additional time needed to process raw images has been greatly reduced but it still requires an extra step in workflow.