9VIII said:
jrista said:
Superpixel sounds like what you want. I actually wish that mainstream RAW editors like Lightroom would offer that as an option, honestly. Some people care more about color fidelity and tonal range than resolution, and having LOTS of pixels with superpixel debayering would be a huge bonus for those individuals.
Using it in post sounds nice, but what we're after is a way to save space on the memory card. Could a camera use superpixel debayering as a part of the image capture process and still save the file in RAW format?
Nope. Once you debayer, or do any kind of processing to the data, your no longer RAW. Canon does offer the sRAW and mRAW settings. Those are what, at best, you could call semi-RAW. They are closer to a JPEG in terms of actual storage format (YCbCr encoding, or luminance+Chrominance Blue+Chrominance Red), but everything is stored in 14-bit precision. It's also encoded such that you have full luminace data, basically a luminance value for every single OUTPUT pixel, but the Cb and Cr data is sparse, it's encoded from multiple pixels (I forget if it is a 1x2 short row, or a full 2x2 quad), and that encoded value is stored as a single pair of 14-bit Cb/Cr values for every 2 or 4 luminace pixels (I think exactly how many color pixels are encoded per luminance pixel depends on whether your sRAW or mRAW). Now the luminace is encoded per output pixel. If your mRAW, I think that's basically 1/2 the area of the full sensor, and for sRAW is basically 1/4 the area of the full sensor. So your luminance information is encoded from however many source pixels are necessary to produce the right output pixels. I think 2x2 for sRAW, something along the lines of 1.5x1.5 for mRAW. (There is a spec on the formats somewhere, it's been a long time since I've read it...my description above is not 100% accurate, but that's the general gist...basically, a 4:2:1 or 4:2:2 encoding of the image data.)
You definitely save space with these formats, but I have experimented with them on multiple occasions, and your editing latitude is nowhere remotely close to a full RAW. You can shift exposure around a moderate amount, but you have limits to how far down you can pull highlights, how far up you can push shadows, how far you can adjust white balance, etc.
9VIII said:
jrista said:
I am guessing it is more than that. Let's say Canon's next move would be to 3.5µm pixels. With a 500nm process, the actual photodiode, assuming a non-shared pixel architecture, would then actually be barely 2.5µm in size at most (once you throw wiring and readout logic transistors around it.) With a shared pixel architecture you might be able to make it a little larger. On the other hand, if you drop from a 500nm process to a 180nm process, the photodiode area could be close to 3.14µm. (This assumes that wiring and transistors only require a single transistor's width border around the photodiode...it's usually not quite that simple, at least based on micrograph images of actual sensors and patent diagrams.) With a 90nm process, the photodiode could be up to 3.3µm.
I think the 500nm process is really limiting for Canon now. They COULD do it, there is nothing that prevents them from creating a 3.5µm pixel sensor with 2.5µm photodiodes...but I don't think it would be competitive. The smaller photodiode area wouldn't gather as much light as competitors sensors that are fabricated with 180nm or 90nm processes, and they would just be a lot noisier.
I am really, truly hoping Canon has moved to a significantly more modern fabrication process with the 7D II sensor. I think that alone would improve things considerably for Canon's IQ.
I'm guessing the only reason you mention 90nm and not 30nm is that in this application the cost/benefit ratio favours slightly larger circuits rather than smaller? (you'd only gain minimal surface area but potentially make production much more difficult)
Well, I mention 180nm and 90nm because I am pretty sure Canon has the fab capability to manufacture transistors that small. In the smallest sensors, transistor sizes are a lot smaller than that...I think they are down to 32nm for the latest stuff, with pixels around 1µm (1000nm) in size. I think that some of Canon's steppers and scanners can handle smaller transistors, 65nm using subwavelength etching, but I don't know if that stuff has been/can be used for sensor fabrication. I know for a fact that Canon already uses a 180nm Cu fab process for their smaller sensors, so I know for sure they are capable of that. Their highest resolution fabs are around 90nm natively, but again, most of what I've read about them indicates IC fabrication...I've never heard of them being used to manufacture sensors (but there honestly isn't that much info about Canon's fabs...nor who owns them...)