08-30-2012, 07:05 AM
(This post was last modified: 08-30-2012, 07:07 AM by Brightcolours.)
Brightness??
It is not about brightness <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' /> . If you put a red, a blue, and two green cars next to eachother, do the green cars appear more bright? No. But there are two of them! Still no... we see just two of them, not one extra bright.
That is exactly what is the case with the sensor. Just because we sample green at a higher rate than blue and red does not mean we sample green at the same rate as blue and red but with a higher intensity.
It seems like that you are under the impression that for each image pixel one red, one blue, and two green pixels get grouped together. And the values just get added, so green gets twice as bright. This of course is not the case. If it were the case, the horizontal resolution and vertical resolution of the sensor would be halved.
What actually happens is that for each pixel, the captured colour filtered light (whether the filter was for the red part of the spectrum, blue part or green part) gets interpolated with the other colours from neighbouring pixels. The intensity of the red, the blue and the green is left alone.
Green is just sampled at a higher frequency. The green data has more resolution, not a higher intensity or more brightness.
Also, the red, the blue and the green values of RGB pixels get stored next to eachother in images. For images with 16 bit bit depth, each colour channel has its own 16 bits, combining to 48 bits per pixel. For 8-bit bit depth they combine to 24 bits per pixel. The calculated red, green and blue values do not influence eachother there either.
It is not about brightness <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' /> . If you put a red, a blue, and two green cars next to eachother, do the green cars appear more bright? No. But there are two of them! Still no... we see just two of them, not one extra bright.
That is exactly what is the case with the sensor. Just because we sample green at a higher rate than blue and red does not mean we sample green at the same rate as blue and red but with a higher intensity.
It seems like that you are under the impression that for each image pixel one red, one blue, and two green pixels get grouped together. And the values just get added, so green gets twice as bright. This of course is not the case. If it were the case, the horizontal resolution and vertical resolution of the sensor would be halved.
What actually happens is that for each pixel, the captured colour filtered light (whether the filter was for the red part of the spectrum, blue part or green part) gets interpolated with the other colours from neighbouring pixels. The intensity of the red, the blue and the green is left alone.
Green is just sampled at a higher frequency. The green data has more resolution, not a higher intensity or more brightness.
Also, the red, the blue and the green values of RGB pixels get stored next to eachother in images. For images with 16 bit bit depth, each colour channel has its own 16 bits, combining to 48 bits per pixel. For 8-bit bit depth they combine to 24 bits per pixel. The calculated red, green and blue values do not influence eachother there either.