Canon EOS 5D Mark IV Dual Pixel RAW Exposed! What Can It Really Do?

by planetMitch2 Comments

Before the Canon EOS 5D Mark IV was even announced, there were rumors circulating about this new thing called Dual Pixel RAW and there were some insane guesses as to what it could be and do. I decided not to publish those rumors because I thought them just too wild.

I was right.

But I was also a bit wrong with my guess that it wouldn't be too significant either.

I've been digging (as I suspect many of you peepers have as well and I've found some of those who have early copies of the Canon EOS 5D Mark IV diving in and making some discoveries about Dual Pixel RAW. This is a summary of what I've found…

But first, a .gif from a Swedish site – noting that this is a small section of a larger photo. The initial photo was focussed on the woman. (Note: here's a BIGGER image where you can see it more effectively)

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I'd say that's pretty significant!

There are some details below but here's a summary:

Another thing I've learned over the weekend is that there are a TON of pixel peepers who love diving into the insane details like this (and it is way beyond my current knowledge level to be frank).

Dual Pixel RAW some details about the ‘focus shift'

Focus shift

The site Kamera&Bild has a sample (which I converted to the .gif above – note again it was a 35mm f1.4 so maybe that contradicts ‘dphog' below?)

The new “Dual Pixel RAW” allows you as a photographer ask for clarity of hindsight – but how is that possible? I have tested the technology to see how it works.

Imaging-Resource also has a sample video:

DPreview has an article talking about Dual Pixel RAW focus shift and they weren't that impressed… but maybe it has to do with lens selection? Let's talk about that:

Now about those lenses where it is effective?

dphog talks about the different lenses he used in testing and says anything below 85mm didn't show any value in using the focus shift – but note again the .gif at the top of the article was a 35mm f1.4 so maybe that contradicts ‘dphog'? In his 5D4 hands on review here (I've started it at 7:27 for you where he talks about his testing of the different focal lengths):

dphog has a rather extensive example of the different lenses

Now about that additional dynamic range:

This is where things really start to go above my head… the peepers win here.

The folks at RawDigger have some very detailed analysis of what's going on in what they're seeing in the two ‘subframes' of a Dual Pixel RAW image, but this snippet from imaging-resource explains it pretty well:

Properly processing a Dual Pixel RAW exposure can provide you with a full stop of additional highlight detail, potentially allowing you to salvage a shot that was accidentally overexposed — at least, so long as you were willing to put up with the huge file size of a Dual Pixel RAW file, as in the 5D Mark IV each such image weighs in at around a hefty 72MB, twice as large as a standard raw. Without any further ado, we'll let Iliah do the talking, and explain just how he came to the realization that Dual Pixel RAW could be repurposed to work in this manner!

And this follow up from RawDigger themselves:

A Canon 5D Mark IV sensor contains two sets of pixels, A and B. Charge stored in pixels of each set is converted into a 14-bit value. The main subframe is formed by (A + B) values, the auxiliary subframe contains only A pixels values. The CR2 format for the Canon 5D Mark IV is also 14-bit, thus the values in the main subframe are limited by 14 bits, with the maximum allowed number being 16,383.

Given the limitation on the number of bits, when A and B are added together to form the main subframe, the result for each pair of sub-pixels needs to be clipped to 14 bits. In other words, suppose, neighboring A and B sub-pixels have a value of 8,000; the resultant sum in the main frame is 16,000, and this is OK, the result can be represented in 14 bits, because it is less then 16,383. But as soon as the sum is greater then 16,383, the result is clipped to 16,383. For example, if neighboring A and B sub-pixels have a value of 10,000, the resulting sum for those sub-pixels recorded to the main subframe will be not their straight sum, 20,000 (as 20,000 can't be represented in 14 bits, it exceeds 16,383). Instead, the respective resulting value in the main subframe will be clipped to 16,383. In the auxiliary subframe, however, we will have 10,000 and no clipping, since 10,000 < 16,383.

As you can see from the above, where the main subframe contains clipped values, the auxiliary subframe may contain true, non-clipped values. That is how that additional ≈1 stop of headroom in highlights for the auxiliary subframe emerges.

Given the mechanism behind the formation and recording of dual-pixel raw data, there is no relation to the size or shape of the highlight area.

Now, again, I realistically don't understand all that, but the images included in the article will help a lot! I urge you to go read that and see

And the question remains… will we be able to have access to that additional stop? Some of the discussion I've seen suggests that may not be possible but maybe DPP is already taking care of that? More to learn!

So, what we know is that we still don't know a lot! HA!

What about the dynamic range without Dual Pixel RAW? This thread at fredmiranda.com says that it is about 13.3 at ISO 100. We'll have more on that soon I hope.

(cover photo credit: snap from Kamera&Bild)



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