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Often it is even 50% green, 25% red and 25% blue pixels. There are different patterns, though. What you get as "megapixel" number of cameras counts subpixels in

Often it is even 50% green, 25% red and 25% blue pixels. There are different patterns, though. What you get as "megapixel" number of cameras counts subpixels individually, that is a "10MP" labelled camera does not have 10 million pixels of each color but 10 million subpixels in total. https://en.wikipedia.org/wiki/Bayer_filter https://en.wikipedia.org/wiki/Bayer_filter If you have a device that can output RAWs, you can look at a RAW image using the FOSS photo development program "Darktable". Choose "photosite color" as the "demosaic" filter to show the individual color channel values (and thereby the Bayer pattern of your camera). But yes, after removing the filter, you have three times the number of pixels but you lost color information.

falcrist 5y ago
Since the "pixels" are either formed at every intersection of 4 photosites (overlapping each other) or by interpolating data for each color to include the "missing" photosites (which is effectively the same), the megapixel count should fairly accurately represent both the number of photosites and the number of pixels in the output image. I'm not exactly sure how the edge pixels are treated, but the difference in number between pixels and photosites should be on the order of a few thousand at most.
- deleted 5y ago
  [deleted]
- barbazoo 5y ago
  Are you saying that one photosite might be included in more than one pixel and therefore the overall pixel count is roughly equal to the number of photosites?
  - falcrist 5y ago
    I'm saying that each photosite definitely is included in more than one output pixel, and I'm also saying that the number of output pixels should be about the same as the number of photosites. This is obviously capturing less information than if you had a completely separate set of photosites for each pixel, but the megapixel count of cameras is nevertheless accurate. Modern cameras sometimes come with a "pixel shift" function, which uses the image stabilization system to take 4 images each shifted one photosite from the others to construct an image where each pixel contains the information of 4 independent photosites with no sharing between the pixels. The resolution of the final image is the same as a normal image, but the result is much clearer, and far less likely to suffer from blue/red moire.
- ansible 5y ago
  > I'm not exactly sure how the edge pixels are treated ... It is quite common to have more than the "nominal" number of pixels in a sensor array. So there are extra pixels for the edges.
  - falcrist 5y ago
    Ah yes. I had forgotten about this. I believe there are also extra pixels at the edge of some sensors that are unexposed, and just used for calibration purposes.
dr_zoidberg 5y ago
Demosaicing algorithms are very good at restoring the resolution "lost" to the BFA. They can introduce some artifacts (zipper effect, "labyrinth", fringe color, to name a few) but in general, sharpness isn't lost as much as people imagine. Nowadays they classical algorithms are being replaced by convnets that are trained on different BFA/image pairs and can get very good results -- at the cost of placing a convnet in the middle (so much higher computational cost, which can be offloaded to a GPU/AI accelerator if available). If you want to see what a "pixel perfect" camera gives you, there are the Sigma cameras with Foveon sensors[0] or you can check the cameras that have a sensor-shift superresolution approach (some pro Olympus and Hasselblad models have this feature). Sensor-shift SR has the problem that it works best on static scenes, because it takes several images which are then later combined on a single picture, and if there's movement between the images it may introduce a few artifacts. [0] which do full color data for every pixel, as they use silicon depth to filter wavelenth
- passivate 5y ago
  Foveon sounds great in theory, but it doesn't deliver IMHO. It can achieve parity in terms of pixel level sharpness and color at the lower ISOs, but picture quality breaks down very quickly even at moderate ISOs. https://tinyurl.com/yyrndzkk https://tinyurl.com/yyrndzkk https://tinyurl.com/t9nnadc https://tinyurl.com/t9nnadc
  - gsich 5y ago
    OT: why URL shortener? This is not twitter with a length restriction.
    - passivate 5y ago
      I've ran into issues with forum s/w URL sanitizers mangling URLs from DPReview. Maybe I should have just tested it. Here we go! https://www.dpreview.com/reviews/image-comparison/fullscreen?attr18=daylight&attr13_0=sony_a7riv&attr13_1=sigma_sdquattroh&attr13_2=apple_iphonex&attr13_3=apple_iphonex&attr15_0=raw&attr15_1=raw&attr15_2=jpeg&attr15_3=jpeg&attr16_0=100&attr16_1=100&attr16_2=32&attr16_3=32&attr126_0=1&attr126_1=1&normalization=compare&widget=1&x=-0.009858951175406968&y=0.32586318515321544 https://www.dpreview.com/reviews/image-comparison/fullscreen...
karmakaze 5y ago
I always wondered if this was a good ratio. I get that green usually has the strongest signal and thus better low-light performance. For bright shots, I find that preserving higher resolution in blue results in higher perceptual resolution of the final image. You can simulate something like it by using an extreme 'night mode' more-red/no-blue display mode and watching a 4k video.
- dr_zoidberg 5y ago
  Green was chosen because it's to what the human eye is most sensitive. Look at Fuji's X-trans[0], and there are also RGBW arrays that prioritize dynamic range. All in all, the BFA is "good enough" most of the times. For the use cases where it isn't, you're either: * Budget constrained and can't really afford not using BFA * Able to (pay for and) use either a color wheel in front of your sensor, or go with prism + triple sensor. * Bite the bullet and go with a "strange" color array. You'll probably need to work on the software side for demosaicing to get proper support and fix eventual artifacts. [0] even more green! 20/36 photosites are green, 8 red 8 blue [1] with W being white, meaning no color filter or "panchromatic cell". In theory this helps on dim light conditions.
  - NathanielK 5y ago
    Good info, but your citations are a bit jumbled up Doctor.
    - dr_zoidberg 5y ago
      Yeah, the [1] was about RGBW
  - karmakaze 5y ago
    The requirements for sensors is different than displays. I guess I was asking why the non-rectangular displays didn't have more blue than green or red as that would improve perceived resolution more.
- NathanielK 5y ago

falcrist 5y ago

Since the "pixels" are either formed at every intersection of 4 photosites (overlapping each other) or by interpolating data for each color to include the "missing" photosites (which is effectively the same), the megapixel count should fairly accurately represent both the number of photosites and the number of pixels in the output image. I'm not exactly sure how the edge pixels are treated, but the difference in number between pixels and photosites should be on the order of a few thousand at most.

deleted 5y ago
[deleted]
barbazoo 5y ago
Are you saying that one photosite might be included in more than one pixel and therefore the overall pixel count is roughly equal to the number of photosites?
- falcrist 5y ago
  I'm saying that each photosite definitely is included in more than one output pixel, and I'm also saying that the number of output pixels should be about the same as the number of photosites. This is obviously capturing less information than if you had a completely separate set of photosites for each pixel, but the megapixel count of cameras is nevertheless accurate. Modern cameras sometimes come with a "pixel shift" function, which uses the image stabilization system to take 4 images each shifted one photosite from the others to construct an image where each pixel contains the information of 4 independent photosites with no sharing between the pixels. The resolution of the final image is the same as a normal image, but the result is much clearer, and far less likely to suffer from blue/red moire.
ansible 5y ago
> I'm not exactly sure how the edge pixels are treated ... It is quite common to have more than the "nominal" number of pixels in a sensor array. So there are extra pixels for the edges.
- falcrist 5y ago
  Ah yes. I had forgotten about this. I believe there are also extra pixels at the edge of some sensors that are unexposed, and just used for calibration purposes.

dr_zoidberg 5y ago

Demosaicing algorithms are very good at restoring the resolution "lost" to the BFA. They can introduce some artifacts (zipper effect, "labyrinth", fringe color, to name a few) but in general, sharpness isn't lost as much as people imagine. Nowadays they classical algorithms are being replaced by convnets that are trained on different BFA/image pairs and can get very good results -- at the cost of placing a convnet in the middle (so much higher computational cost, which can be offloaded to a GPU/AI accelerator if available). If you want to see what a "pixel perfect" camera gives you, there are the Sigma cameras with Foveon sensors[0] or you can check the cameras that have a sensor-shift superresolution approach (some pro Olympus and Hasselblad models have this feature). Sensor-shift SR has the problem that it works best on static scenes, because it takes several images which are then later combined on a single picture, and if there's movement between the images it may introduce a few artifacts. [0] which do full color data for every pixel, as they use silicon depth to filter wavelenth

passivate 5y ago
Foveon sounds great in theory, but it doesn't deliver IMHO. It can achieve parity in terms of pixel level sharpness and color at the lower ISOs, but picture quality breaks down very quickly even at moderate ISOs. https://tinyurl.com/yyrndzkk https://tinyurl.com/yyrndzkk https://tinyurl.com/t9nnadc https://tinyurl.com/t9nnadc
- gsich 5y ago
  OT: why URL shortener? This is not twitter with a length restriction.
  - passivate 5y ago
    I've ran into issues with forum s/w URL sanitizers mangling URLs from DPReview. Maybe I should have just tested it. Here we go! https://www.dpreview.com/reviews/image-comparison/fullscreen?attr18=daylight&attr13_0=sony_a7riv&attr13_1=sigma_sdquattroh&attr13_2=apple_iphonex&attr13_3=apple_iphonex&attr15_0=raw&attr15_1=raw&attr15_2=jpeg&attr15_3=jpeg&attr16_0=100&attr16_1=100&attr16_2=32&attr16_3=32&attr126_0=1&attr126_1=1&normalization=compare&widget=1&x=-0.009858951175406968&y=0.32586318515321544 https://www.dpreview.com/reviews/image-comparison/fullscreen...

karmakaze 5y ago

I always wondered if this was a good ratio. I get that green usually has the strongest signal and thus better low-light performance. For bright shots, I find that preserving higher resolution in blue results in higher perceptual resolution of the final image. You can simulate something like it by using an extreme 'night mode' more-red/no-blue display mode and watching a 4k video.

dr_zoidberg 5y ago
Green was chosen because it's to what the human eye is most sensitive. Look at Fuji's X-trans[0], and there are also RGBW arrays that prioritize dynamic range. All in all, the BFA is "good enough" most of the times. For the use cases where it isn't, you're either: * Budget constrained and can't really afford not using BFA * Able to (pay for and) use either a color wheel in front of your sensor, or go with prism + triple sensor. * Bite the bullet and go with a "strange" color array. You'll probably need to work on the software side for demosaicing to get proper support and fix eventual artifacts. [0] even more green! 20/36 photosites are green, 8 red 8 blue [1] with W being white, meaning no color filter or "panchromatic cell". In theory this helps on dim light conditions.
- NathanielK 5y ago
  Good info, but your citations are a bit jumbled up Doctor.
  - dr_zoidberg 5y ago
    Yeah, the [1] was about RGBW
- karmakaze 5y ago
  The requirements for sensors is different than displays. I guess I was asking why the non-rectangular displays didn't have more blue than green or red as that would improve perceived resolution more.
NathanielK 5y ago