Why iPhone RAW is a Big Deal

iOS 10 brought the capability to get the RAW image data from the camera and save it as a DNG file. It elevates the quality of iPhone images to a whole new level (for those who care). The following image tells it all.

Click the image for actual pixels display on non-Retina screens

Click the image for actual pixels display on non-Retina screens

On the left is how the iPhone renders the image, on the right my version converted from DNG and tweaked to taste in Capture One. Both show the actual pixels (100% magnification). Red areas are the overexposed parts. The images were captured as RAW+JPG in the upcoming Mark II Artist’s Viewfinder 5.0, so they represent the exact same moment.

With shooting RAWs you can avoid most of the pitfalls of iPhone image processing (I know them from experience):

  • Over-sharpening, which ruins images with already high contrast edges, such as tree branches against the clear sky.
  • Excessive noise reduction – usually on an unnecessary level, even at ISO 25. You know, the blotchy look at 100% which looks downright ugly.
  • Unrealistic color. Apple processes the images for punch, which is good for making your friends envious on social networking sites, but is a problem when you want to actually use them (the images, not your friends) as real photographs.
  • Sometimes overdone light falloff correction. You know, when the sky is brighter in the corners than in the center.

You also get more headroom for recovering overexposed areas (they are also better by default because of the lower contrast), but on the other hand you need to correct corner light falloff by hand.

To my eye the difference is so large that I won’t use JPGs any more when I’m photographing with the iPhone (which happens a lot, since it’s always in my pocket). No, they are not challenging DSLR (or even large sensor point and shoot) quality, but are way more usable than the JPGs.

Dual Pixel RAW and Kuuvik Capture

Dual Pixel RAW is Canon’s new invention that will see its first release with the EOS 5D Mark IV. There’s some vague marketing info floating around, but haven’t seen a concise description of these files yet. So while updating Kuuvik Capture’s (websitemy posts) RAW decoder to support the 5D Mark IV, I had a chance to dig deeper into Dual Pixel RAWs.

To understand the following discussion, you need to know how Canon’s Dual Pixel AF works, especially how these Dual Pixels are divided into two separate photodiodes. This article by Dave Etchells gives you a thorough explanation.

What is a Dual Pixel RAW file?

Normal CR2 files contain the following sections:

  • Metadata
  • Previews
  • RAW data

The DPRAW file is a CR2 file that contains one more additional section:

  • Metadata
  • Previews
  • RAW data
  • DPRAW data

This organization have a very important implication. Any RAW processing software that does support the normal 5D Mark IV files will be able to open DPRAWs. If the app is unable to interpret the DPRAW data part, it will simply ignore it and will work with the file as a normal RAW. There’s no risk or penalty in taking DPRAWs (besides the huge buffer drop from 21 to 7 frames).

The DPRAW file contains the normal RAW data section to make this compatibility possible, plus one side of each pixel in the DPRAW data section.

The RAW data section contains pixel values with the sum left and right sides of the photodiode, while the DPRAW section contains pixel values from just one side of each photodiode.

The RAW data section contains pixel values with the sum of left and right side photodiodes, while the DPRAW section contains pixel values from just one photodiode of the two.

But how do we get the other side of each pixel to let Dual Pixel aware processing apps do their tricks? It’s easy: since the RAW pixel value is the sum of left and right pixel sides, just subtract the DPRAW pixel value from the RAW pixel value.

This is an unusually clever implementation from Canon, where I’m used to see all kinds of inflexible hacks that look like as if they were designed in the 1980s.

Size-wise, DPRAW files are slightly less than double the size of normal RAWs (since metadata and preview images are stored only once).

How will Kuuvik Capture 2.5 handle DPRAWs?

Not being a RAW converter, Kuuvik Capture needs the RAW data for two purposes: the RAW histogram as well as shadow/highlight warnings (the image displayed on the screen comes from the preview embedded in each CR2 file). For these the RAW data section is totally sufficient, and the app will ignore the DPRAW data section if present in a CR2 file.

The app will display normal RAW and DPRAW files equally fast, but downloading DPRAW files from the camera will take almost twice as much time as normal RAW (because of their larger size).

I assume that there will be a possibility to switch the camera into DPRAW mode remotely (I can’t be sure until my rental unit arrives). If that is the case, then a new preference will let you specify whether you’d like to shoot RAWs or DPRAWs.

Shooting a Waterfall in the Rain

One of the things I had learned during the last decade is that image making is a pursuit that involves a healthy amount of plastic bags and gaffer tape to solve various problems.

Let’s take the following image for example.

Smooth and Rough

Smooth and Rough

There was a light rain when we arrived, not to mention the water droplets from the waterfall that the wind slammed in our face. It was a blessing to walk the scene with the Mark II Artist’s Viewfinder with no need to open the backpack and soak several lenses just to find a composition.

In my favorite composition (of the several I tried in just a few minutes) I wanted to emphasize the clash of dark rough rocks and light smooth water. So I needed a long exposure to smooth out the water flow. Unlike the 5DS R, none of my Zeiss lenses are weather sealed. And water accumulating on the LEE Big Stopper is also problematic. Since I don’t carry an umbrella (which would be the trivial solution), I used the largest water-resistant thing in my bag: the Shadepirate flag in the plastic bag I used to carry it in.

Shadepirate flag functioning as an umbrella

Shadepirate flag functioning as an umbrella

Some extra light also came from the direction of rain/water so the flag actually served double-duty. The setup worked quite well, and had to wipe just a small amount of water from the filter between exposures.

Focus Stacking with the Otus 1.4/28

Last weekend I had a little time to play with the Otus 1.4/28. I was at Lake Tisza, but the light was suboptimal to put it mildly. So I decided to make a test shot to check how focus stacking will work with the Otus 28.

Why would you need focus stacking in the first place with such a wide angle? Well, if you have a brutal 50 megapixel sensor, with a lens that’s sharper in the corners than most lenses in the center, you don’t want to throw that resolution away by stopping down below the diffraction limit.

For this test I ended up using f/6.3 and taking 6 slices.

Early Spring Pier, Lake Tisza

Early Spring Pier, Lake Tisza

It was a quite a bit windy, and I wanted to smooth out the waves using the 10-stop LEE Big Stopper. I had to realize that I ran out of gaffer tape (unfortunately the Big Stopper on the Otus 28 leaves quite a gap at the sides), so I used my heavy cotton dark cloth to keep unwanted light from hitting the front element.

The dark cloth covered the entire camera, but it was quite easy to focus on the 11″ screen of my MacBook Air using Kuuvik Capture. The images were focus stacked in Photoshop CC.

And the result? Perfect front-to-back, corner-to-corner sharpness. It’s simply amazing.