What Is Dual-Pixel RAW in the Canon 5D Mark IV?

Canon’s newest 5D Mark IV camera has a lot of exciting specifications — the fast frame rate and 4K video capabilities, for example — but there is more to this camera than what first meets the eye. One new feature buried in Canon’s promotional material is a technology called Dual Pixel RAW. This isn’t something that we have seen before, but it seems like it could be one of the most interesting features of this new camera. So, what is Dual-Pixel RAW?

1) What Dual Pixel RAW Isn’t

Before we get to what Dual Pixel RAW is, let’s talk about what it isn’t. First, although they have similar names, the Canon 5D Mark IV’s Dual Pixel RAW is not the same as its Dual Pixel Autofocus. Instead, Dual Pixel Autofocus is a way for the camera to use phase-detect autofocus in the camera’s live view, making for better autofocus in video and better live-view focus on moving subjects. This is a useful feature, but not the same as Dual Pixel RAW.

Dual Pixel RAW also, unfortunately, is not a way to improve the resolution of a photograph. Some cameras, like the Pentax K-1, use pixel-shift technology to make images appear significantly sharper. Although we don’t have all the details on Canon’s Dual Pixel RAW yet, it definitely does not work by moving the camera’s physical sensor (which means it also cannot be used for sensor-based image stabilization). Instead, it uses the left and right halves of a single pixel to create a photo, as discussed later.

2) What Is Dual Pixel RAW?

At the moment, we only know what Canon has said, and they haven’t said very much. Let’s start by looking at the quotes in their promotional material:

“The EOS 5D Mark IV’s Dual Pixel CMOS AF system enables capture of Dual Pixel Raw (DPRAW) files. Images shot as DPRAWs have conditional adjustment possibilities when processed with Canon’s Digital Photo Professional image processing software, which enables pixel-level adjustment and refinement for still photographs and includes Image Micro-adjustment to help maximize sharpness in detail areas, Bokeh Shift for more pleasing soft focus areas and Ghosting Reduction to help reduce aberrations and flare.“

There’s also this gem:

“When lens diaphragm setting is fully open, adjustment volume and compensation effect are emphasized. Sufficient adjustment volume and compensation effect may not be achieved, depending on lens in use and shooting conditions. Adjustment volume and compensation effect vary depending on camera position (landscape or portrait).”

Reading through these — several times — you can get some sort of an idea how Dual Pixel RAW works. As I see it, there are three main ways to use this feature:

1. You can shift the focus of a photograph after it has been taken. This isn’t nearly to the degree of light-field cameras like Lytro, but it will allow you to shift the focus a few millimeters in one direction or another. I see a lot of portrait photographers appreciating this feature — shifting the focus of a crucial photo from your subject’s eyelashes to their eyes.
2. You can change the appearance of a photograph’s out-of-focus regions, both in the foreground and the background. They don’t provide many more details than this, so I’m speculating, but my guess is that you can shift the out-of-focus regions from left to right, creating more pleasant bokeh. I’ll update this as more information is available.
3. You can reduce the flare and ghosting from a bright light source in your frame. I see the reason why this feature could work (explained in the next section), but I’m still waiting to see it before I’m fully convinced. As a landscape photographer, this feature seems almost too good to be true, especially if it completely eliminates flare, or comes close. We’ll need to wait and see how well it works, but I wouldn’t hold out hope for more than a slight reduction in flare.

As the name implies, these adjustments are done to the RAW file that you capture. This is essential, and I am glad that Canon didn’t make this a JPEG-only feature.

3) How does Dual Pixel RAW Work?

Canon’s Dual Pixel RAW works by taking two photos, both 30.4 megapixels in size, using the left and right halves of a single pixel. Because the two halves see things a bit differently, Canon lets you filter information from them separately. For example, the two halves of each pixel will have slightly different amounts of flare, since flare sometimes hits one side of a pixel more strongly than the other. The same principle is used to shift a photo’s focus and bokeh appearance.

This is similar to the way that Lytro’s cameras worked, but to a much lesser degree. By capturing light from two different perspectives, Canon gives just the slightest hint of what a light-field camera can capture — but it does so without sacrificing the high 30.4 megapixel count.

4) Caveats for using Dual Pixel RAW

Based on the information that Canon has released, there seem to be a few drawbacks/caveats related to using the Dual Pixel RAW feature. I’ll go through them individually:

Post-Processing

All of these adjustments have to be made in post-processing. There is no way to eliminate ghosting or flare with this feature while you are actually taking pictures, for example. At this point, too, the only software that allows for these corrections is Canon’s own Digital Photo Professional software. Hopefully, companies like Adobe will add the ability to adjust these files as time goes by, although I tend to think it is unlikely (Update: Adobe has said that they are “working on” making this feature compatable with their software — a very welcome addition!).

Does it always work?

Their own material seems to say that Dual Pixel RAW doesn’t always work perfectly. If you use certain lenses (presumably depending upon focal length), you might see more or less of an effect. Or, interestingly, your choice of camera orientation — landscape or portrait — also changes the effectiveness of Dual Pixel RAW. We haven’t seen anyone test these claims yet, so I don’t know if these are just covering-all-our-bases marketing statements, or if they are things that you’ll actually notice yourself.

Aperture settings

It seems that Dual Pixel RAW works best at wide aperture settings (“When lens diaphragm setting is fully open, adjustment volume and compensation effect are emphasized”). This would make sense, simply because the slight adjustments possible would be harder to see with a small aperture, where depth of field is much larger.

One Adjustment Per Photo

You can only do one adjustment to a photo, not all three at once. So, if you need to adjust focus and reduce flare, you have to pick one of the two. This shouldn’t be a huge problem, but it is worth keeping in mind.

File Size Concerns

Unfortunately, file size almost doubles when you use the Dual Pixel RAW feature, from 37 MB to 67 MB, which is an obvious concern. If you’re shooting a wedding, for example, it might be nice to have these features at your disposal — but not worth doubling the total file size of the entire wedding

Frame Rate Effects

As far as I can find, Canon doesn’t mention anything about a reduction in frame rate with the Dual Pixel RAW feature. There certainly may be a reduction in frame rate — it wouldn’t surprise me — but I haven’t heard anything about it yet. Stay tuned.

5) Video Demonstration

Imaging Resource released a video demonstration for the focus shifting adjustments. It seems pretty interesting, so I recommend watching for yourself:

The focus shifting feature seems pretty solid — not for large adjustments, but certainly for some photos. Because this adjustment is relatively small, it seems like the earlier quote from Canon (“When lens diaphragm setting is fully open, adjustment volume and compensation effect are emphasized”) was referring to a simple effect: you’ll notice this more if you shoot at a wide aperture.

The video doesn’t give much insight into the other two features, flare reduction and bokeh shift. Hopefully we will see video demonstrations of these effects in the coming days and weeks.

6) Conclusion

No one has the 5D Mark IV on hand to test this feature yet, but it certainly seems promising. As a landscape photographer, my hope is that the flare reduction feature actually works well enough to use — if it does, that could justify the almost-doubled file size for a given image. Although there are ways to reduce a photo’s flare already, they take more post-production effort than I tend to enjoy, and they also require taking two photos.

For portrait photographers, the focus shift feature clearly appears very useful. And, although they haven’t given us many details on the bokeh shift feature, I assume that it also works fairly well. Even a small adjustment to the out-of-focus regions of an image can affect a photo’s composition significantly, and it’s always good to have options. I also see these two features as potentially very useful for macro or wildlife photography. The only problem — and why I think that many people will not use this feature — is that the Dual Pixel RAW files take up roughly twice as much space as standard photos. For high-volume shooters, that simply won’t work.