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Preface
Before the DNG format is released, let us first understand what is the original unprocessed image format output by SLR cameras, Apple and Android mobile cameras?
RAW
What is RAW?
RAW is an unprocessed and uncompressed format. RAW can be conceptualized as "original image encoded data" or more vividly as "digital negative".
RAW is the raw data in which the CMOS or CCD image sensor converts the captured light source signal into a digital signal.
That is to say, a RAW file is a file that records the original information of a digital camera sensor, and also records some metadata (Metadata, such as ISO settings, shutter speed, aperture value, white balance, etc.) generated by the camera shooting.
Each pixel of the sensor corresponds to a color filter, and the filters are distributed according to the Bayer pattern . Directly output the data of each pixel, that is, RAW RGB data .
Raw data (Raw RGB) becomes RGB after color interpolation, as shown in the following figure:
How is RAW data generated?
Through SLR cameras, Apple and Android mobile cameras, the captured scenery is projected onto the sensor through the lens to generate an optical image. The sensor converts the optical image into an electrical signal. The electrical signal is then converted into a digital signal through analog-to-digital conversion, and the digital is stored. The signal file is also a RAW file.
What is the difference between RAW and jpeg?
RAW data is directly stored unprocessed digital signal.
Image formats such as jpeg are data that have been modified and optimized by ISP and then lossy compressed.
Why give up RAW, the origin of DNG
Because RAW data standards are not unified
RAW is an unprocessed file. The original image file only records all parameters on the sensor, including original exposure, exposure, white balance, tone, color, style and other data.
The problem is that each camera and mobile phone manufacturer has its own RAW format for privatization and customization, so there are no unified specifications and standards to define RAW. Each camera and mobile phone manufacturer needs special software to view and edit their own RAW formats. RAW format.
The DNG standard was released as early as 2015, and the latest DNG 1.7.0.0 standard specification was released by Adobe in June 2023.
At present, all SLR cameras, Apple, Huawei, Xiaomi, OnePlus and other mobile phone manufacturers have supported the DNG format to output raw image data (DNG).
DNG wants to unify raw data standards
Digital Negative (DNG)
is a public archiving format used to store raw data files generated by a variety of digital cameras. There has been a lack of an open standard for raw data files created by various camera models, and Digital Negative solves this problem by ensuring photographers can easily access their files.
In addition to the Digital Negative Specification, Adobe also provides the free Adobe DNG Converter. There is no software download address here. If you are interested, you can download it from the official website.
List of supported camera attempts: https://helpx.adobe.com/cn/camera-raw/using/supported-cameras.html
Since the DNG format is relatively new, there are currently not many software that supports the DNG format. Basically only Adobe's own software can support it: Photoshop, Photoshop Elements, Lightroom and Lightroom Classic, etc.
FFmpeg currently cannot support the DNG format, but due to the special relationship between DNG and TIFF, you can open it with ffmpeg by changing the suffix of DNG to TIFF. Therefore, for developers, the amount of development is a bit large for the time being, because the time for the specification to be launched is too short, and the open source library is expected to have to wait for a while.
The relationship between TIFF, TIFF/EP, DNG, RAW
TIFF and DNG are both Specifications. They define file formats with the suffix .tif/.tiff and .dng respectively. At the same time, the TIFF Specification also defines a baseline and some extended tags.
TIFF/EP defines and standardizes TAGs used in electronic images.
DNG is compatible with both TIFF and TIFF/EP, and contains EXIF and XMP information. DNG is actually an expanded TIFF. You can directly preview the image by changing the extension of DNG to TIF.
DNG format standard specification
Download address: https://download.csdn.net/download/eguid_1/88335365
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