With the introduction of the Nikon D4S and the D810, Nikon introduced the new sRAW format for saving images. While we have already explained the format in detail in our sRAW format explained article, there were many follow-up questions from our readers, some of whom asked us to provide some image samples from RAW, sRAW and JPEG formats to compare things like white balance recovery and highlight / shadow recovery. In this article, we will explore the sRAW format in detail and show sample images from both controlled lab and outdoor environments, demonstrating what sRAW is capable of delivering when compared to the regular RAW format.
First, let’s take a look at how capable the sRAW format is at recovering white balance. For the first test, we photographed a color chart with the D810 in proper white balance, then changed the WB setting to 2500K (cool) and 10000K (warm). The below comparisons demonstrate the results in both sRAW and JPEG formats to show their differences compared to regular RAW files.
sRAW White Balance Recovery: Controlled Environment
Here is a crop from a color chart shot with correct white balance:
We will be using the above as a reference to compare to colors produced by sRAW and JPEG. Below is the output of sRAW, shot at 2500K and then recovered to 4900K, which is the correct WB (Left: sRAW, Right: JPEG)
Although the difference between the first RAW and sRAW files is pretty small, a slight change in colors is definitely there. In addition, there is a drastic change in exposure – when I changed the WB to 4900 in Lightroom, the sRAW image appeared visibly brighter. In order to make a proper comparison, I had to decrease the exposure on the sRAW file by -0.7 stops (explained why further down below). Still, it is pretty clear that sRAW contains more data than JPEG, since the color output of JPEG appears drastically different when recovered similarly from 2500K.
Take a look at the below crops that compare the other end of the color spectrum, at 10000K:
For this comparison, I had to adjust sRAW by -0.5 stops to make it comparable. Again, sRAW demonstrates much better white balance recovery than JPEG. Take a look at what happened to white and gray shades of color – they appear blue. Many other colors are not reproduced accurately either.
If you compare the RAW and sRAW files, they appear to yield similar colors, although sRAW definitely renders the colors a bit differently due to loss of colors. Remember, we are dealing with 11-bit data compared to 14-bit, so there is a definite loss of data. Comparing sRAW and JPEG, is 11-bit vs 8-bit, which is approximately 8.6 billion colors compared to only 16.8 million.
Still, sRAW is drastically better than shooting in JPEG format, as the above examples demonstrate.
How does this apply to real world shooting? Let’s take a look at the below outdoor samples for a comparison.
sRAW White Balance Recovery: Outdoor Environment
For this study, we will be using the below image as a reference, with white balance set to 5600K:
Now let’s take a look at how it compares to sRAW and JPEG, both of which were set to 2500K, then recovered to 5600K in Lightroom (Left: sRAW, Right: JPEG):
Although the first indoor test showed some differences in color, the above samples demonstrate what happens to both sRAW and JPEG images when wrong white balance is used. Although I tried everything I could to imitate the JPEG output to the original RAW file, none of my attempts resulted in correct rendering of blues and greens in the above scene. It is a given that JPEG is a poor choice when compared to either sRAW or RAW file formats. Now if you compare RAW to sRAW, there is still a visible change due to loss of colors. Pay attention to the change of colors and shades in the front two trees and some greens – they appear warmer on sRAW files, which is false color.
Now let’s take a look at what happens at 10000K, recovered back to 5600K:
Now we see sRAW rendering colors a bit cooler in comparison, which is also the result of loss of colors. The difference is not dramatic, but it is definitely there. The warmer colors were easier to recover for the JPEG format, so it does not appear as bad as before.
sRAW Shadow and Highlight Recovery: Adobe Camera RAW
The above sample images demonstrate that the sRAW format preserves many more colors than the JPEG format, which is definitely good news for those that consider using this format. We definitely see loss of colors when compared to the RAW format, but it is not as bad as JPEG. But what happens when one tries to actually recover both highlight and shadow details? Whether one is a landscape, architecture or lifestyle photographer, being able to recover images is important, especially when shooting in high contrast scenes. Let’s see what happens to images when they are over-exposed by four stops, then recovered in post. Here is a comparison of the three formats (Left: RAW, -4 EV Recovery, Right: sRAW, -4 EV Recovery, Bottom: JPEG, -4 EV Recovery):
Now this is where things get very interesting. The difference in what a 14-bit RAW file can yield compared to an sRAW appears to be drastic when recovering highlights. The JPEG format is obviously the worst here, as it cannot even deal with such a change in exposure, which ends up simply darkening the blown out highlights.
Here is what happens if we push the exposure by -3 stops, then attempt to recover:
The RAW file only loses data in some areas that are exposed beyond 4-5 stops, but most of the colors and details are there. Now compare the result to sRAW – the difference is again very noticeable. And JPEG is yet again not able to deal with such changes in exposure, resulting in a darker image. Here, one could argue that the JPEG output actually looks better than sRAW, particularly when comparing the grass area close to the center of the frame.
Now let’s see what happens if we underexpose images heavily by -5 stops, then attempt to recover the data in post:
This is where I got confused when looking at the above shots. I could not believe that JPEG actually looked better than sRAW! At first, I thought that I did something wrong on the camera, so I went back and re-shot the scene. When I compared my first attempt with the second, the results were the same. I then tried to recover the same details, but this time in Nikon’s Capture NX-D to see if anything would come out any different. Below is what I found out.
sRAW Shadow and Highlight Recovery: Nikon Capture NX-D
When I compared how Nikon’s Capture NX-D software rendered the same image, I was very surprised – the result was very different compared to what ACR did. Take a look at the same -4 EV comparison, this time rendered by Capture NX-D:
The sRAW format is visibly worse than RAW, but not as bad as it was before, which shows that Adobe Camera RAW is simply not ready to work with this format. Capture NX-D renders the sRAW file much better and the difference is quite obvious.
What about underexposing by five stops and recovering? See the results for yourself:
Looks much better! Now the output is very comparable to that of the JPEG file. When looking at pixel-level data, the sRAW and JPEG contain visibly more noise than RAW files.
This was an interesting study, because it showed what sRAW can and cannot do when compared to RAW and JPEG files. If your intention is to be able to recover white balance, the sRAW format has a definite advantage over JPEG as demonstrated in the first part of the article. Although there is definite loss of colors, you can recover most of the data when altering white balance, which is good news. Hence, if you want to have smaller RAW files and have the flexibility to change white balance, the sRAW format seems to be a viable option.
However, when it comes to recovering information from shadows and highlights, the sRAW format must be used with caution. First, you should not be using Adobe Camera RAW (Photoshop and Lightroom) for sRAW file conversion, since the Adobe RAW engine ends up heavily under-exposing images and losing more data in highlights, as demonstrated above. Capture NX-D clearly does a better job, but the software is very buggy and has its own set of problems (for example, recovering a normal 14-bit RAW file in ACR yields better results compared to NX-D). Second, you need to carefully evaluate the above image samples and decide if you are ready to potentially lose some of that valuable data that can be vital when recovering shadow and highlight details. The sRAW format seems to be somewhere in-between JPEG and RAW – it is not as bad, but definitely not anywhere as good as what a RAW file can yield.