The RGGB model takes advantage of this sensitivity by capturing twice the amount of green pixels, resulting in a perceptually brighter image.Ī hot pixel in a pre-demosaic image - only one pixel is affected This pattern mimics the characteristics of the human eye: we perceive more brightness than colour, and our eyes are significantly more sensitive to green light compared to red or blue light. This is called demosaicing.Ĭameras can use a variety of mosaic patterns, but a commonplace pattern is a 2x2 RGGB (Red, Green, Green, Blue) matrix.
Since each pixel only contains brightness information for one colour, the other two colours must be interpolated using information from neighbouring pixels.
Raw photo processor file size full#
It’s then up to the software to interpolate these mosaic patterns using the appropriate Bayer matrix and produce a full colour output. The sensor data is in a greyscale, mosaic format. Light passes through this filter onto the sensor’s photosites, but the sensor doesn’t capture ‘colour’-rather, it captures brightness values. You’ll notice that the image we’re working with is greyscale-so where’s the colour? Most cameras use what’s called a colour filter array in front of the sensor-this is often a Bayer filter.
Similar to the white point remapping, we can approximate a gamma tone curve by using a Curves adjustment: This is because the RAW sensor data is encoded as linear we perceive light in a non-linear fashion, however, where the shadow range is expanded and the highlight range is compressed, so we’ll want to account for this. We’ll also want to do some gamma conversion. Whilst rudimentary, for the purposes of demonstration we can achieve this by using a simple Levels adjustment, bringing the white point right down to remap it. This is because we count 0 as a value too (absolute black) within the range of bits. Notice the maximum values are 655, rather than 655. The RAW file I’ve chosen is 12-bit, so we need to remap its brightest pixel value-4095-to the equivalent in 16-bit, which would be 65535. For our purposes, the unprocessed image data is represented in 16-bit, which contains 65,536 levels. 12-bit contains 4,096 levels, for example, whilst 14-bit contains 16,384 levels. Most RAW data is captured at 14-bit or 12-bit precision, which determines the levels of brightness the image can contain. Without wanting to get too complicated, this is due to the captured sensor information’s bit depth. at first glance, it’s a little underwhelming. Let’s strip all that away and look at an unprocessed image. Certain RAW tools allow us to extract this data before any significant processing is applied to it. Now we know what’s in a RAW file, let’s take a closer look at the sensor image data.
It’s often used to preview the image on the camera’s LCD screen, and can be used for initial previewing in RAW processing software whilst the actual RAW file is being processed and thumbnailed in the background.
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