Shadowblade
15th of June 2009 (Mon), 12:25
Let's face it - the megapixel race is running out of steam. Sure, we can produce more and more crowded sensors, with less and less noise, while increasing pixel density, but, as yet, we cannot break the laws of physics. With the latest generation of cameras (5DII, 50D and 500D) we are running into diffraction limitations at larger and larger apertures - f/7.6 in the case of the 50D. Also, we are running into problems with high-resolution sensors outresolving lenses. Cramming more megapixels into a sensor of the same size won't solve anything - all it means is 30 blurry megapixels with the same image quality as a 10-megapixel image and a 30MP file size and noise level. In effect, the only way to increase your image quality further by increasing megapixel count is by increasing the sensor size, with corresponding increases in size, weight and cost, of bodies and lenses.
But this need not mean a slowing of improvement in image quality - raw megapixels are only part of the equation. Hence, my wishlist for Canon's next generation of cameras:
1) How about a 5DIII with 21 true megapixels? Or even 12 true megapixels?
Due to their use of Bayer interpolation, current DSLRs are rather optimistic in their pixel count. A 21MP camera has just 5.25 million 'real' sets of RGB values, while a 12MP camera has just 3 million sets. The rest are interpolated from these sets of RGB values, in a similar vein to extra pixels being interpolated from existing pixels when enlarging an image in Photoshop (but obviously using a different technique). Meanwhile, the 21MP sensor, with only 5.25 million sets of RGB values, suffers the diffraction limits and noise levels associated with cramming 21 megapixels onto a small piece of silicon...
Professional video cameras have not one, but three CCDs - one each for red, green and blue. Each sensor is full-sized, with the same resolution as the final image. After passing through the lens, light is split into three streams, each being captured by a CCD. The three images - one red, one green, one blue - are then combined, in a similar manner to the red, green and blue channels of a digital image in Photoshop. Other sensors (e.g. the Foveon X3) do not require the splitting of incoming light, but which use a three-layered sensor to capture the three coloured images. This results in an image with the same true resolution as the sensor resolution, with no Bayer interpolation required and no corresponding loss of image quality. A 12 megapixel trilayer sensor will produce an image with 12 million 'real' sets of RGB values, not 3 million.
In effect, a 10MP, 3-sensor (or trilayer sensor) image will have larger photosites, a much greater diffraction limit and a smaller file size than a 21MP sensor using Bayer interpolation, while maintaining twice the level of detail of the 21MP sensor.
Which brings me to my next point:
2) Bigger pixels mean less noise and more dynamic range.
This is simple physics. A bigger photosite captures more photons, resulting in a greater difference in light between a full photosite (maximum intensity, or 'white') and a photosite empty apart from random signal noise (minimum intensity, or 'black'). The ratio between maximum and minimum is the dynamic range. Increasing this ratio gives a more vibrant image with greater highlight and shadow detail - often much more important than a nominal increase in megapixel count. A 2-stop increase in dynamic range would result in every photo taken having the dynamic range of a 3-shot HDR (taken at -1, 0 and +1), while a 4-stop increase would result in a similar dynamic range to a 5-shot HDR (taken at -2, -1, 0, +1 and +2). These cover the full dynamic range (or close enough to it) of almost any photo. Similarly, the relatively lower level of random signal noise means lower noise and higher ISO capability.
Naturally, a greater dynamic range means a greater difference between black and white. Since the data is saved in a digital format, this means a greater difference between each level of intensity in the file saved to the CF card. More levels means smaller differences, which mean less banding in the final image - particularly when manipulating the image in DPP, Lightroom, ACR or Photoshop. Fortunately, modern microprocessors are more than up to it. Which brings me to my final point:
3) What about true 16-bit output?
A great deal of photo manipulation this day is done with 16-bit files - photoshop PSD as well as TIFF format. Once saved onto the hard drive in such a format, the camera's 14-bit output will end up taking up the same space as a 16-bit file anyway, with a quarter the number of intensity levels. There is little reason the sensor's data can't be saved in 16-bit format in the first place.
Canon - please produce a full-frame, 12MP DSLR using either three sensors or a trilayer sensor, with true 16-bit output. I'd pay top dollar for it. I don't need thirty million washed-out, noisy, with 22.5 million of them being interpolated anyway. Give me 12 million real, vibrant, clean pixels, with the same level of detail as 48 million Bayer-interpolated pixels (and a greater diffraction limit, less noise, more dynamic range and a smaller file size) any day!
But this need not mean a slowing of improvement in image quality - raw megapixels are only part of the equation. Hence, my wishlist for Canon's next generation of cameras:
1) How about a 5DIII with 21 true megapixels? Or even 12 true megapixels?
Due to their use of Bayer interpolation, current DSLRs are rather optimistic in their pixel count. A 21MP camera has just 5.25 million 'real' sets of RGB values, while a 12MP camera has just 3 million sets. The rest are interpolated from these sets of RGB values, in a similar vein to extra pixels being interpolated from existing pixels when enlarging an image in Photoshop (but obviously using a different technique). Meanwhile, the 21MP sensor, with only 5.25 million sets of RGB values, suffers the diffraction limits and noise levels associated with cramming 21 megapixels onto a small piece of silicon...
Professional video cameras have not one, but three CCDs - one each for red, green and blue. Each sensor is full-sized, with the same resolution as the final image. After passing through the lens, light is split into three streams, each being captured by a CCD. The three images - one red, one green, one blue - are then combined, in a similar manner to the red, green and blue channels of a digital image in Photoshop. Other sensors (e.g. the Foveon X3) do not require the splitting of incoming light, but which use a three-layered sensor to capture the three coloured images. This results in an image with the same true resolution as the sensor resolution, with no Bayer interpolation required and no corresponding loss of image quality. A 12 megapixel trilayer sensor will produce an image with 12 million 'real' sets of RGB values, not 3 million.
In effect, a 10MP, 3-sensor (or trilayer sensor) image will have larger photosites, a much greater diffraction limit and a smaller file size than a 21MP sensor using Bayer interpolation, while maintaining twice the level of detail of the 21MP sensor.
Which brings me to my next point:
2) Bigger pixels mean less noise and more dynamic range.
This is simple physics. A bigger photosite captures more photons, resulting in a greater difference in light between a full photosite (maximum intensity, or 'white') and a photosite empty apart from random signal noise (minimum intensity, or 'black'). The ratio between maximum and minimum is the dynamic range. Increasing this ratio gives a more vibrant image with greater highlight and shadow detail - often much more important than a nominal increase in megapixel count. A 2-stop increase in dynamic range would result in every photo taken having the dynamic range of a 3-shot HDR (taken at -1, 0 and +1), while a 4-stop increase would result in a similar dynamic range to a 5-shot HDR (taken at -2, -1, 0, +1 and +2). These cover the full dynamic range (or close enough to it) of almost any photo. Similarly, the relatively lower level of random signal noise means lower noise and higher ISO capability.
Naturally, a greater dynamic range means a greater difference between black and white. Since the data is saved in a digital format, this means a greater difference between each level of intensity in the file saved to the CF card. More levels means smaller differences, which mean less banding in the final image - particularly when manipulating the image in DPP, Lightroom, ACR or Photoshop. Fortunately, modern microprocessors are more than up to it. Which brings me to my final point:
3) What about true 16-bit output?
A great deal of photo manipulation this day is done with 16-bit files - photoshop PSD as well as TIFF format. Once saved onto the hard drive in such a format, the camera's 14-bit output will end up taking up the same space as a 16-bit file anyway, with a quarter the number of intensity levels. There is little reason the sensor's data can't be saved in 16-bit format in the first place.
Canon - please produce a full-frame, 12MP DSLR using either three sensors or a trilayer sensor, with true 16-bit output. I'd pay top dollar for it. I don't need thirty million washed-out, noisy, with 22.5 million of them being interpolated anyway. Give me 12 million real, vibrant, clean pixels, with the same level of detail as 48 million Bayer-interpolated pixels (and a greater diffraction limit, less noise, more dynamic range and a smaller file size) any day!