How does Dual Pixel RAW (DPRAW) work, and how can users make the best of it? The developers of the EOS 5D Mark IV tell us in Part 3 of this interview. (Interviewer: Ryosuke Takahashi, Group photo: Takehiro Kato)

 

 

What is DPRAW?

- Can you explain in simple terms the basic system and the working principles of the new DPRAW feature?

Nashizawa: DPRAW images are a RAW image format which incorporates image information from two different viewpoints, obtained from the CMOS sensor. Parallax information that arises from a difference in viewpoint is made use of on the Dual Pixel RAW Optimizer function in Digital Photo Professional (DPP) Ver. 4.5.0 to carry out various types of post-processing edits to images.

- What was it that led to the development of DPRAW in the first place?

Tachibana: When we were developing a dual pixel format for the sensor, we were already aware that this technology could be used for carrying out various post-processing edits to still images. After repeated trials in the development stage, we finally managed to put it into shape on the EOS 5D Mark IV in the form of a new DPRAW shooting function.

- Dual Pixel RAW images involve the acquisition of image information from two viewpoints. Does this mean that this feature is available only during Live View shooting?

Tachibana: No. DPRAW images are basically RAW images that are amended with information from two viewpoints, and they can be recorded to the media during both Live View shooting and viewfinder shooting. You just need to set Image quality to “RAW”, and then enable Dual Pixel RAW in the camera menu. You can also perform image corrections later on the DPP. However, do note that the size of a DPRAW image is about twice that of a normal RAW image due to the larger amount of information it contains.

 

 

- Could you tell us briefly about each of the image correction effects?

Nashizawa: As the names suggest, Bokeh Shift is a feature for shifting the position of the (foreground or background) bokeh effect, while Ghosting Reduction reduces ghosting or flare due to reasons such as backlight with the use of the Dual Pixel RAW Optimizer. Image Microadjustment is a feature for correcting the apparent resolution using the depth information of the subject such as when the subject has moved slightly.

 

 

- Is there any condition that allows the effects of the Dual Pixel RAW Optimizer to show up more easily?

Nashizawa: In principle, effects of some kind will appear when you capture a DPRAW image, but there are indeed conditions for such effects to show up more prominently. First of all, effects for all the areas corrected become more noticeable when the aperture setting is f/5.6 or lower. We also recommend using an ISO speed of 1600 or below. Do also take note that the effect may vary depending on whether the image is vertically or horizontally oriented.

- Is the correction effect also influenced by factors such as the focal length and shooting distance of the lens in use?

Nashizawa: Yes. For the Image Microadjustment feature, for example, a lens focal length of 50mm or longer is ideal. The correction effect also becomes more prominent when the distance from the subject is larger, although there exists a “best distance” for each focal length.
For a lens of the 50mm class, the best distance from the subject is between about 1m and 10m, while that for a 100mm class lens would be between about 2m and 20m. In the case of a 200mm class lens, a shooting distance between about 4m and 40m is ideal for bringing out the effects of Image Microadjustment, Bokeh Shift and Ghosting Reduction.

Tachibana: The best distance here means that the subject falls within the distance range. However, even when the recommended conditions are met, the magnitude of the effect may vary according to the scene. In fact, the effect you obtain from the actual correction is not very dramatic, so it would be best to see it as a tool for touching up the image you have captured.

 

Image Microadjustment useful for portraits and other genres

- While it is ideal to capture the facial expression and movement of the hair in a portrait, the resulting shot may not appear sharp if there is any slight movement in the subject. So am I right to say that applying Image Microadjustment in this case helps to produce desirable results?

Tachibana: Yes, I think it is best to understand the feature as one for ensuring good results when you want to fine-tune the apparent resolution in situations like this one. I find that using the feature in combination with a lens that has a bright f-number and a shallow depth of field particularly helps to increase your chances of obtaining an excellent shot.

- Is it possible to perform correction that only increases the apparent resolution of the pupil instead of that at the corner of the eye?

Nashizawa: It depends on the shooting conditions, but I believe correction at that level is possible. However, the result may vary according to the shooting conditions, so we are unable to provide specific figures with respect to the extent of the correction.

 

 

 

- When photographing shots such as a nightscape, any slight tilt in the lens might lead to changes in the ghosting and flare. Can I understand correction by DPRAW as something that also makes use of this phenomenon?

Tachibana: Yes, you are absolutely right that it makes use of difference that arises in this state. Just like there are ghosting (and flare) that can be eliminated and those that cannot, some types of ghosting can be reduced in DPRAW images but not other types, so we hope our users can understand that ghosting is not completely removed in the same way as when you use image editing software.

- I find it a very useful feature. Is there any restriction on the shooting functions when using Image Microadjustment?

Nashizawa: The number of possible shots and the maximum burst during continuous shooting are smaller, and the maximum continuous shooting speed becomes approximately 5 fps. Also, it cannot be used in combination with Multiple Exposure, HDR shooting, Digital Lens Optimizer and One-touch Image Quality Setting.

- Can I carry out image adjustments in the same way that I would for RAW images even when DPRAW is selected?

Nashizawa: Yes. DPRAW images are saved as ordinary RAW images in the same format with the same file extension, so it is possible to perform image adjustment using the DPP.

 

Use of Dual Pixel RAW Optimizer is recommended for final photo touch-up

- Please tell us what points we should take note of when making adjustments using the Dual Pixel RAW Optimizer.

Nashizawa: First of all, the outline of the subject or bokeh effect may become unnatural when Bokeh Shift is used, and there might also be more noticeable noise or changes in the colour or brightness. When these are observed, try to weaken the level of Bokeh Shift. Doing so can also help to improve the effect when the apparent resolution affects the depth of field or when the selected region in the image turns out unnatural due to the large amount of adjustment.
For Ghosting Reduction, the outline of the subject or bokeh effect may become unnatural, noise may increase, and changes in the colour or brightness may become more prominent. In such cases, you can correct the apparent resolution in the same way as what you do for Bokeh Shift to resolve these issues.
Another point to note is that you are unable to apply different types of correction at the same time.

- Is Ghosting Reduction affected by the type of light source?

Nashizawa: No. Ghosting Reduction does not differentiate the type of light source, but makes use of only the DPRAW image information from two viewpoints. It can be applied regardless of whether the ghosting or flare occurs under a natural or an artificial light source. However, the resulting effect varies depending on the strength of the ghosting (or flare) as well as the shooting conditions.

 

 

- When we feel that the apparent resolution is somewhat lacking, it is important to tell whether the Dual Pixel RAW Optimizer would help to achieve the desired effect, or whether the lower apparent resolution is caused by lens aberration, am I right?

Tachibana: Yes, you are right. During RAW image processing, users will need to determine whether to use Dual Pixel RAW Optimizer or to apply Digital Lens Optimizer for correcting lens aberration based on the image to be adjusted. In this sense, this feature is suited for users with a relatively high level of skills.

- For the Dual Pixel RAW Optimizer, is it necessary for us to develop an intuitive feel of how strong the effects are?

Tachibana: The only way is for users to familiarise themselves with the effects. We do not want our users to take a less precise shot with the assumption that adjustments can be made later using this feature. Rather, they should continue to produce accurate shots as before and use this as a tool for the final photo touch-up.

 

For a more in-depth explanation of the three ways you can post-process DPRAW images, check out the following article:
EOS 5D Mark IV Tips: 3 Handy New DPP Features for Correcting DPRAW Images

 

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