What information does a RAW image file contain besides the image data?
Asked 2/3/2020
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I understand a normal image as a 2D array of pixels, where each pixel has RGB color values. What does a camera RAW file actually store instead? Does it contain more than just image data, and how is that data different from a finished RGB image?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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A RAW file does not consist of pixels with multiple color coordinates. It consists of a single value from each sensor well on the sensor. Those values must be demosaiced by an algorithm that has some knowledge of the Bayer or other filter that sits in front of the sensor wells. These algorithms take the value of each well and those from some small neighborhood of other wells, and generates an RGB pixel value for that location.
RAW files also typically include one or more pre-processed JPEG preview images, EXIF and other metadata, and maybe some other stuff, all packaged into some sort of "archive" file (some use TIFF containers with different sections for the different types of data, but that's not universal), and probably with some level of compression applied.
Originally by user68706. Source · Licensed CC BY-SA 4.0
user68706
6y ago
0
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A RAW file usually does not store a finished RGB value for every pixel. Instead, it stores one brightness/luminance measurement from each sensor photosite (sensor well). Because most sensors use a color filter array such as a Bayer pattern, each photosite records only one filtered sample, not full red, green, and blue values.
To create a normal color image, software must interpret the sensor pattern and run demosaicing, using neighboring samples to estimate full RGB pixels.
RAW files also often include additional data such as:
- camera metadata (EXIF and related information)
- one or more embedded JPEG preview images
- information about the sensor/filter layout
- compression and container structure specific to the camera maker
So the key difference is that RAW is closer to the original sensor readout, while JPEG/TIFF-style images usually contain already processed RGB pixels.
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