## Mark II Artist’s Viewfinder 5.0 Available

Version 5.0 of my Mark II Artist’s Viewfinder app is now available on the App Store. It took quite a bit longer than I first planned, but if you look at the sheer number of new stuff, you’ll understand why. More work went into this update than it took to develop the original version 1.

I wrote about the black & white mode and exposure compensation, and the question of RAW capture in former posts, now it’s time to reveal everything else. I’ll touch a few new things in this post, and highly recommend to take a look on the complete list in the release notes. And pay attention to the “Changes” section.

Quick Control Screen

The are a few subtle visual changes to make it less cluttered, and to make room for two new icons. The half dark/half light icon in the upper right toggles black & white mode. The 2x icon switches to the telephoto camera if you have an iPhone 7 Plus. The telephoto camera and wide converter use are mutually exclusive (as one would logically expect).

Icons for parallax correction/shift simulation and aspect ratio changing are now white when a non-default value is set for these (in the above example I set the 5DS R virtual camera to 16:9 aspect ratio).

Album -> Catalog

We had to rename the Album to Catalog to avoid a name clash with the thing that Apple calls an album in the Photos app. Now ours is named Catalog, since it would be extraordinarily hard to convince Apple that they should change…

And while we are talking about the Catalog, there are performance improvements here and there, meaning that an update may be required to the new format. The app automatically detects if this is the case, and will update the Catalog automatically.

Availability

This is a free update for existing Mark II Artist’s Viewfinder owners. New user can purchase the app for \$26.99 / €26.99.

We offer upgrade bundles for former Viewfinder Basic/Pro/Cine edition owners, so they can upgrade for a reduced price.

The Viewfinder Handbook was also updated to cover all the new features.

## 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

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:

• Previews
• RAW data

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

• 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 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.

## RAW File Bit Depth Changes with ISO

Let’s begin with the fact. The usable bit depth of your RAW file depends on the ISO used to shoot the image.

I discovered this while working on the RAW histogram feature in Kuuvik Capture. To make the RAW histogram usable, we have to scale the data coming from the RAW file. This scaling ensures that the left side of the histogram represents pure black and the right side represents pure white. Technically scaling is done by first subtracting the black level from each pixel, then mapping pixel data from the [0, white saturation] interval into the [0, 1] interval.

Black level is the value your sensor emits when no photons reach a given pixel. This is calculated utilizing a black masked area along the edges of the sensor (see my former post on this).

White saturation is the value from the given pixel when it’s completely full – that is more photons reaching the pixel will not generate a higher value. This depends on physical attributes of the sensor. We do a series of measurements for each sensor to determine its value. The higher the white saturation the more tones your RAW file contains.

What surprised me during the initial white saturation measurements is that with most of Canon’s cameras this value changed as I changed the ISO. Some cameras even present different white saturation in different exposure modes (Av and M for example).

The following graph shows the result from these measurements converted into usable bit depth for four cameras up to ISO 6400.

For the mathematically inclined, usable bit depth is calculated with the formula:

$\log_2 (w - b)$

Where $w$ is the white saturation and $b$ is the black level.

The roughly 0.3 bit difference between the lowest and highest values doesn’t seem that large at first sight, but this means that you lose 15% of the tones at ISO 640 compared to ISO 800. To put it another way it’s a 1/3 stop difference.

Implications

Avoid non-full-stop ISOs.

The truth is that both ISO 500 and ISO 320 are exposed at ISO 400, putting a 1/3 stop “digital exposure compensation” value into the RAW file. For the ISO 320 setting this produces an overexposed image, which should be pulled down 1/3 stop. The downside is that you lose 1/3 stop of both tonal and dynamic range. The upside is that there will be less perceived noise, which can be helpful in some situations (and which is the basis of lots of false myths)

Avoid ISOs < 200 on crop-sensor Canons.

As you can see on the graph above, bit depth on these machines are less below ISO 200 than on or above it.