Linear DNG versus Linear Profile

I previous wrote a blog regarding the RAW and JPEG outputs from the various camera modes from Samsung S23 Ultra (https://jimmy1photo.wixsite.com/blog/post/samsung-s23-ultra-camera).

In this blog, I will focus and dive deeper into S23 Ultra's RAW outputs.

Samsung smartphone RAW output is in DNG format. This is my first time working with DNG file, and I had to learn as I go. Then I found out there are some unique differences to Samsung's DNG files versus typical RAW images from other cameras I have used (Nikon, Canon, and Sony). These differences impact how the post processing is done. So it is important for me to standardize my workflow, for both shooting and post process. Then I can apply a customized profile to all my RAW images, and then fine tune according.

Here is the a summary of what Samsung Pro mode and Expert RAW mode outputs. The term "linear" appears in multiple places. And they mean very different things.

	DNG Format	Profile
Pro Mode	Linear DNG	Standard Profile
Expert RAW Mode	Linear DNG	Linear Profile

RAW Format

Typical image sensor captures the data in Red, Green, and Blue channels. And typically they are laid out in a Bayer pattern.

The RAW image file contains unprocessed data for each channel. Then it is up to the RAW processor/editor to combine that info into what we see as the colored image. This process is demosaicing.

DNG Format: Normal vs Linear

Adobe introduced DNG (Digital Negative) format. This was supposedly to standardize lossless format, as every camera make (and often model) will have unique proprietary RAW format.

Then there are 2 different types of DNG files. Normal DNG is a RAW format; Linear DNG is non-RAW format. Linear DNG is non-RAW because the data is already partially developed or processed. The demosaicing is already done and baked into the file. In addition, linear DNG might also include denoising and lens correction. You can read more about linear DNG in this DXO article: https://www.dxo.com/tech-news/linear-dng/

Samsung's Pro Mode vs Expert RAW Mode:

I use RAWTherapee (RT), which is a free open source RAW editor. One impact is some features and tools are disabled with linear DNG. These tools are coded to operate on standard RAW image with raw RGB data. With demosaiced linear DNG file, these features are no longer available. An example is Capture Sharpening tool in RT.

Both Samsung Pro mode and Expert RAW mode output in linear DNG format. This is a non-RAW format. Although both output the same format, the amount of processing is very different, particularly in detail and sharpening.

Here 100% crop of 2 images. Left is Pro mode. Right is Expert RAW mode.

You can see the significant difference in color fringing and sharpening. Pro mode (left crop) has some color fringing and looks soft. Expert RAW (right crop) has no color fringing and has much more sharpening.

There is additional processing baked into the Expert RAW output. I can guess what is happening here:

	DNG Format	Processing Done	Profile
Pro Mode	Linear DNG	Demosaic	Standard Profile
Expert RAW Mode	Linear DNG	Demosaic Denoising Sharpening Color de-fringing	Linear Profile

Which is better? Well, it depends on the user. Most users want to use RAW image that has not being processed. That way, users can edit and post-process however we like. When processing is already baked in, these changes cannot be undone. So to me, Pro mode is more flexible (or you can call it "better") than Expert RAW, in that it gives more control to the user.

Profile

These are often called Camera Profile, Processing Profile, or simply Profile. This is applied by the camera into the RAW image. And editors also can apply its own profile to emulate what it thinks the camera and human sees.

In typical RAW files, Standard Profile is non-linear (red curve at right). It is like a gamma correction. This non-linear profile changes the image brightness to what human perceives.

On the other hand, if no correction is applied, then the output is in Linear Profile (straight black line at right). The image will appear flat.

Although most cameras use Standard Profile, recently there are cameras that offer option to output in Linear Profile. There is supposedly more data for manipulation in the linear profile. And this might matter to hardcore landscape photographers.

It is quite surprising why Samsung chose to use Standard Profile for Pro mode and Linear Profile for Expert RAW. Not sure if it is using this as a marketing ploy. People using Samsung smartphone (instead of real camera) already decided that convenience and portability is more important than image quality. The smartphone image quality has improved significantly, but it is still not at level of dedicated cameras. Using smartphone already means taking a hit on image quality; this Standard vs Linear Profile difference is moot.

I was struggling on how to efficiently post-edit the Expert RAW linear profile image, using RawTherapee. I tried manually to get to a point that is reasonable, so that I can start to make my edits. I had some issues with inconsistent results; thus spending time to get the linear profile to look like standard profile. After understanding the Linear Profile, reading up on tonal curves, and help from online photography forums, the solution is quite easy.

Here is a comparison of 3 images from RawTherapee.

1. Left is at import.

2. Middle is intermediate step after Auto-Levels.

3. And right is after applying Adobe Camera Raw default profile curve.

Step 1: When Expert RAW is first loaded into RT, it looks like a black mess. See left image above of the composite. The histogram (below) is completely shifted to the left.

Step 2: Apply Auto-Levels, which typically increases exposure 4- to 5-stops. This centers the histogram (below). Image is still flat though. See middle image above of the composite.

Step 3: RT has a bundled profile/curve that is the default curve used by Adobe Camera Raw. You can read about it here: http://rawpedia.rawtherapee.com/Exposure#Tone_Curves

This is what the Adobe Camera Raw default profile/curve looks like:

I apply this Adobe default profile to the image. The result is the right image in the composite above. And histogram below is resulting tonal curve.

This basically gets the Expert RAW linear profile to a great starting point. Then I can do my edits to customize the image to my preference.

If you are interested in Samsung Galaxy S23 Ultra versus Google Pixel 7 camera comparison, check my write-up here: https://jimmy1photo.wixsite.com/blog/post/s23-ultra-versus-pixel-7-camera