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Author Topic: Canon Dual Pixel Liveview Autofocus  (Read 14839 times)

miejoe

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #30 on: July 02, 2013, 10:43:39 AM »
There's a video on the Canon Global website that shows some nice diagrams and explains the process.

http://www.canon.com/news/2013/jul02e.html

Hopefully the added circutry and the inevitable gap from doubling the number of photoreceptors is very small and gives a minimal loss of SNR.

I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #30 on: July 02, 2013, 10:43:39 AM »

neuroanatomist

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #31 on: July 02, 2013, 10:47:18 AM »
I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

Based on what I've read, including a statement from Chuck Westfall who was asked for clarification on the matter, they are all split in the same direction.  That means the Dual Pixel CMOS phase AF system is a giant vertical line sensor, responsive only to horizontally-oriented details.
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traveller

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #32 on: July 02, 2013, 11:05:13 AM »
I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

Based on what I've read, including a statement from Chuck Westfall who was asked for clarification on the matter, they are all split in the same direction.  That means the Dual Pixel CMOS phase AF system is a giant vertical line sensor, responsive only to horizontally-oriented details.

This will be the 80D's big selling point - "Cross-type Dual Pixel CMOS"  ;D

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #33 on: July 02, 2013, 11:12:51 AM »
I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

Based on what I've read, including a statement from Chuck Westfall who was asked for clarification on the matter, they are all split in the same direction.  That means the Dual Pixel CMOS phase AF system is a giant vertical line sensor, responsive only to horizontally-oriented details.

Any guess as to whether the next generation will have a quad split (2x2) to do both vertical and horizontal or would it be better to use the next neighboring pixel of of the same color instead?

tron

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #34 on: July 02, 2013, 11:18:57 AM »
If they like "playing" with the sensors they might as well make a lower noise/higher DR one  ::)  ;D  8)
(Let the debates begin... )

dilbert

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #35 on: July 02, 2013, 11:30:25 AM »
The best explanation I've seen thus far is on dpreview's website here:
http://www.dpreview.com/previews/canon-eos-70d/3

Each and every of those 20.2 million active pixels that makes up the picture (whether red, green or blue) is divided into two pixels. One for the left phase, and the other for the right phase. They both hide behind one micro lens, and are positioned next to each other (hopefully without any appreciable gap, as that might cause a strange bokeh effect) to receive the phases. Combined, they theoretically cover pretty much the same area as a conventional photodiode, and should give the same light gathering capability. Its no more than pixel binning to recreate a normal image from this sensor, with normal light gathering capabilities.

So in theory this dual pixel configuration should have no detrimental effects on SNR over a conventional 20.2MP APS-C sensor. Let's hope they've used a new sensor fabrication process to manufacture this sensor, to bring along the much anticipated (and reported) improvements in SNR - I'm guessing that was is in effect a 40.4 MP APS-C sensor would be next to impossible to make with the old sensor fabrication process.

You don't get something for nothing.

If space on the sensor is taken up for PDAF sensors next to pixels, then space on the sensor that could be given to the pixel (allowing it to store more photos, for example) is lost.

Even if the half used for autofocus was somehow fed back into the colour, space has to be lost for the boundary between the two.

Or to put it another way, the noise characteristics of the 70D should be about that for a 40MP APS-C sensor using the same sensor technology without the PDAF split.

tron

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #36 on: July 02, 2013, 11:34:54 AM »
Or to put it another way, the noise characteristics of the 70D should be about that for a 40MP APS-C sensor using the same sensor technology without the PDAF split.
But then the two parts are combined to one pixel so it isn't it a kind of pixel binning?

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #36 on: July 02, 2013, 11:34:54 AM »

dilbert

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #37 on: July 02, 2013, 11:41:28 AM »
I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

Based on what I've read, including a statement from Chuck Westfall who was asked for clarification on the matter, they are all split in the same direction.  That means the Dual Pixel CMOS phase AF system is a giant vertical line sensor, responsive only to horizontally-oriented details.

Any guess as to whether the next generation will have a quad split (2x2) to do both vertical and horizontal or would it be better to use the next neighboring pixel of of the same color instead?

What they might be able to do is to have a pattern on the sensor of PDAF cells rather than just straight up and down.

So maybe the new bayer sensor looks like this:

R.I.G.I
I.G.I.B

I = vertical AF sensor and one for horizontal might look like this:

R.-.G.I.R.-
|.G.|.B.|.G
- = horizontally sensitive AF sensor.

Or they might do:

R.-.G.|.R.-
G.|.B.-.G.|

or

R.-.G.|.R.-
G.-.B.|.G.-

but to subdivide all of the pixels again would really cut into the ability of a pixel to capture light for recording the image with.

dilbert

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #38 on: July 02, 2013, 11:49:31 AM »
Or to put it another way, the noise characteristics of the 70D should be about that for a 40MP APS-C sensor using the same sensor technology without the PDAF split.
But then the two parts are combined to one pixel so it isn't it a kind of pixel binning?

That isn't made clear.

Now if it were true then this would impact video photography in interesting ways because to shoot 1/60, that half of the pixel would need to be being sampled at 1/120 - there needs to be time to read the pixel for AF and then let it recharge. So if you were shooting 60fps, all of those pixels would be being exposed at 1/120. Now if you know that's going on then the raw to image processing can take that into account. Why can't the value from the AF read be used for video? Because that's a sample taken before the camera wants to read the sensor for image data to ensure that the lens is correctly adjusted.

For photography it is a different matter - you could pixel bin because the 7fps provides a relatively long pause between times when the pixel/sensor is read.

BruinBear

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #39 on: July 02, 2013, 12:20:51 PM »
According the Canon the EOS 70D's Dual Pixel CMOS AF system has the following key characteristics:

Usable phase detection AF area covers 80% of the frame horizontally and vertically
AF works at apertures down to F11
AF works in light levels as low as 0 EV
Can work with face detection to keep moving subjects in focus

 :o
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alan_k

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #40 on: July 02, 2013, 12:21:49 PM »
This is from the DP-Review hands-on Preview (bold mine)

Quote
According the Canon the EOS 70D's Dual Pixel CMOS AF system has the following key characteristics:

    Usable phase detection AF area covers 80% of the frame horizontally and vertically
    AF works at apertures down to F11
    AF works in light levels as low as 0 EV
    Can work with face detection to keep moving subjects in focus

Does this mean, for example, I could get AF on a 70-300L + 2xTC, and if so, only in live-view?

e: you read my mind!!!  :o
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neuroanatomist

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #41 on: July 02, 2013, 12:24:54 PM »
This is from the DP-Review hands-on Preview (bold mine)

Quote
According the Canon the EOS 70D's Dual Pixel CMOS AF system has the following key characteristics:

    Usable phase detection AF area covers 80% of the frame horizontally and vertically
    AF works at apertures down to F11
    AF works in light levels as low as 0 EV
    Can work with face detection to keep moving subjects in focus

Does this mean, for example, I could get AF on a 70-300L + 2xTC, and if so, only in live-view?

e: you read my mind!!!  :o

Sure...but you could do that with Live View on any camera (although not with phase detect AF).
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Mt Spokane Photography

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #42 on: July 02, 2013, 12:33:38 PM »
I'm also hoping that the pixels aren't all split in a left/right horizontal pattern, as the video shows, but that half of them are split vertically, because no one would want the AF system to be sensitive to horizontal contrast only.

Based on what I've read, including a statement from Chuck Westfall who was asked for clarification on the matter, they are all split in the same direction.  That means the Dual Pixel CMOS phase AF system is a giant vertical line sensor, responsive only to horizontally-oriented details.

That's also what I surmised from Canon's video.  However, I believe that in Portrait mode, the sensor would be only seeing vertical details unless the camera is able to switch between the two automatically, which doesn't seem likely - at least not in a mid range model.
 
I am wondering about things like banding, or a new type of artifact that might appear due to the divided photo sensors.  That's pretty dependent on the actual fine details of how it works, something that we are not going to get from Canon.
 
As to patents, the sensor sounds like it uses this recent patent from Canon.
 
http://translate.google.com/translate?twu=1?sl=auto&tl=en&u=http%3A//egami.blog.so-net.ne.jp/2012-08-12
 
After reading the patent document, I found it to be very complex, but it is almost certainly what we are seeing.
 
The wording is very engineering like, and looks like something intended for a mirrorless camera, which is why it was not anticipated to appear in a DSLR first.
 
While AF is said to be 30% faster, its obviously not yet going to beat conventional phase detect AF for speed.  However, with more computing horsepower as might happen with a dual Digic 5+ processor or a newer version of Digic, we might see the mirror go away for good.
« Last Edit: July 02, 2013, 12:48:22 PM by Mt Spokane Photography »

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #42 on: July 02, 2013, 12:33:38 PM »

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #43 on: July 02, 2013, 12:58:26 PM »
Here is another video showing what the focus pulls look like when you use the touchscreen to focus while you are shooting in live view.  It actually looks pretty nice.  They also have some examples of auto focus ect.  if you watch after the credits in the middle of the video they replay the video with an overlay showing focus info and some metadata.

https://www.youtube.com/watch?v=Tf0BBNr6Epk&feature=player_embedded

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #44 on: July 02, 2013, 07:50:56 PM »
Does it have AFMA?

check the dprevew preview.

The 70D does have AFMA for the traditional 19 point AF sensor (unlike the 60D), but the dual pixel system doesn't need AFMA because the AF sensor & the image sensor are one in the same.
« Last Edit: July 02, 2013, 07:53:20 PM by funkboy »

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Re: Canon Dual Pixel Liveview Autofocus
« Reply #44 on: July 02, 2013, 07:50:56 PM »