If you are a digital photo player then you are very familiar with image formats such as JPG (pretty common), TIFF ... These formats use the technique of "compression with data loss" (lossy compression), part of the image information will be removed to reduce the file size. But with the RAW format, the only people who specialize in digital photography use this format.
RAW characters are not necessarily characters from the beginning, but they are roughly raw. RAW is also common to many image file formats of manufacturers such as .CRW, .CR2 from Canon; .ORF of Olympus ;; .MRW of Minolta or .NEF of Nikon.
What is RAW?
It can be said that the raw file contains all the data that the sensor in the digital camera recorded while shooting. Each vendor has a method to encode the sensor data into a & quot; raw image & quot; But in all cases, the information in the raw file is preserved.
Digital cameras use a variety of technologies to process and transfer information, but almost all RAW cameras use the & quot; (mosaic sensor); Also known as the color filter array (color filter array CFA) two-dimensional. Each unit cell represents a pixel (pixel) in the image.
But photosensitive cells are only responsible for converting the amount of photons that light receives into electrical signals, so the information that raw files receive from color filters is grayscale.
How the camera turns into an RGB color image
Except for some newer cameras using the Foveon sensor ("Sigma Foveon X3 Technology", it is capable of independently recording three RGB colors.) Most of the CCD and CMOS sensors are now mounted on the array. The red, green, and blue-filtered sensory cells produce millions of small, interlaced cells in a certain order.
Not only does the data capture pixel information, the raw file contains the metadata of the snapshot. Metadata, semantically, is & quot; data data & quot; (metadata), created by the camera every time. In metadata, both JPEG and RAW formats have an EXIF file (Exchangeable Image Format) that contains information about camera operations such as camera type, serial number, speed, flash, focus, flash mode
In addition to each value in the grayscale scale, most RAW formats contain a decoder ring in the metadata to pass information about the arrangement of color filters in the sensor to the RAW converter. . As a result, raw converters can convert images from grayscale grayscale images into a color image by & quot; modulation & quot; Interpolate colors that are missing from the pixels that match the specific color-changing algorithms of each camera manufacturer. This process is called & quot; transplant & quot; (demosaicing), the key task of the transfiguration, but not yet complete. The RAW conversion process has the following additional steps:
- The white balance that you set on the digital camera when shooting has no effect on the pixels when shooting in RAW mode; This information is only written to the receiver in the metadata. Many transmitters use this information to call the default white balance but there is some self-analysis of the image to choose the optimal white balance.
- Interpretation of colorimetric interpretation. Each pixel in a RAW file saves a numerical representation of red, green, blue. But red, green, illuminate & quot; ambiguous & quot; By asking 100 people get 100 different reds. There are many color filters used on cameras, so the RAW converter must assign color exactly to the conventional color scale; For example, CIE YXZ rulers are set up in terms of human color perception.
- Gamma correction. RAW images with linear gamma are very different from those on film, so the RAW converter must correct the gamma to suit the human eye.
- RAW converters use a variety of algorithms to reduce grain, anti-aliasing, detailing, etc.
What is the difference between JPEG and RAW?
When you take pictures in JPEG format, the RAW converter in the digital camera performs all of the above steps to turn the raw image into a color image and compress it in JPEG compression. Some cameras allow users to choose parameters such as color (sRGB, Adobe RGB), sharpness, contrast. This is a lot of work if you have to constantly change the parameters from one image to another, so many of you are entrusted to the camera. JPEG does not use much editing ability and due to compression of information, so when you adjust, you easily falsify other factors; including skin color.
But when shooting with the RAW format you have almost complete control over the ability to interpret from the image information. When shooting RAW, the camera only governs the ISO, shutter speed and aperture. Everything else is under your control. For example, you can adjust the white balance, the color distribution, the tint, the sharpness, the smoothness of the details, ... You can even balance the compensation. Most RAW cameras record 12 color bits (equivalent to 4,096 color shades) per pixel; While, JPEG limits 8 bits per channel. So when shooting JPEGs, the camera's transducer gets rid of a lot of useful information.
The correlation between JPEG and RAW formats is similar to negatives in film and slide films. JPEG is like a slide film for accurate recording right at the moment and limited in the ability to edit later. Raw is a negative film because it allows for color correction, color balance ... after shooting. RAW also has a lot of potential in the digital camera manufacturers' transformation.
Digital photos are no longer in their infancy, but they are not yet mature. The current JPEG format is fairly common, but the creative space on JPEG is modest. Over the next ten years, there will be significant changes in color filters and RAW formats that will allow you to fully exploit the potential of raw images. Many people have referred to RAW as the digital image format of the future.
