Own An X-T1? For Low Light, Is It Better To Increase The ISO Or Just Underexpose And Adjust In Your Editor?

Indoor test subject under incandescent light; X-T1 w/18-55mm lens; ISO 200; 0.5 sec. @ f/8 (click to enlarge)
This image was properly exposed and shows no appreciable digital noise.
(I threw in the 30 year old Kodak Gray Card just for kicks.  Obviously, it has faded over time.  Auto white
balance was very close but I tweaked it using the ColorChecker Passport grayscale.)

If you own a Fujifilm X-T1, do you know if you will you get a better image by raising your ISO when needed or keep your base ISO and then brighten your image to taste in your image editor?  I was wondering that myself so I decided to find out.  I ran the exact same tests with my Olympus E-M1 which you can find here.

I wanted to test my X-T1 to see what differences I could expect by raising my ISO as necessary for any particular conditions as I normally would or just underexpose the image at ISO 200, then brighten the image in Lightroom.  I set up two tests, one indoors and one outdoors.  I placed the camera on a tripod, turned image stabilization off, put it on manual exposure, set auto white balance, set it for raw file format and manual focus.  I planned on testing ISOs from 200 to 6400, the range in which raw files are produced on the camera.  I don't normally use JPEG format, so I didn't test that file type.

In order to keep this blog post relatively short, I will only address the extreme, comparing ISO 6400 correctly exposed and ISO 200 underexposed 5 f/stops.  The results I saw seem to apply to these intermediate images as well as the extremes.

Disclaimer:  These tests are informal and non-scientific and only apply to my particular sample of the camera and under these particular conditions.  Your camera and/or conditions may vary, so just take the results for what they are as one particular example and not valid for all cameras and all conditions.  I don't have any sophisticated testing instruments.  I can only visually look at the results and assess by what I see.  I'm just a photographer trying to better understand his camera and how it reacts in different situations and want to share what I find.

ISO 6400 correctly exposed; 1/60th sec. @ f/8 (click to enlarge)

This image was 5 stops underexposed then brightened to match the properly exposed image in Lightroom 5.7.1.
The camera was set for ISO 200 but the amount of light present required ISO 6400 (click to enlarge)
1/60th sec. @ f/8

Approximately a 100% crop from the ISO 6400 image properly exposed. (click to enlarge)
No noise reduction applied in camera nor in editing. When comparing these to the same images taken with
my Olympus E-M1 (which I am also testing), I noticed that even with no noise reduction,
there is no chrominance noise present (red/blue/green splotches).  Fujifilm must be applying noise reduction to the 
raw files with the user unable to turn it off.

Approximately a 100% crop from the ISO 200 image underexposed 5 stops (ISO 6400 light) (click to enlarge)
Again, a total lack of the telltale red/blue splotches one would expect to find in an image 5 stops underexposed.
There has to be some sort of raw file manipulation going on that the user can't turn off.  That makes me wonder
if Fujifilm is applying some luminance noise reduction to the raw files also?

As you can see there is very little difference in contrast, color, amount of digital noise, or saturation.  Any minor differences could certainly be matched in your image editor.  The histograms show almost no difference, only a very slight shift in position the midtone area, but not enough to say you are losing or gaining raw data with either technique. Both histograms are solid throughout the tonal range from black to white with no "combing" indicating a loss of data.

Here is the outdoor scene.  It was a heavily overcast day.  The results are similar, however, the 5 stop underexposed image shows a bit more contrast.  Other than that, the results are similar to the indoor scene.

This is the outdoor scene; X-T1 w/18-55 lens; ISO 200, 1/80th sec. @ f/8; auto white balance (click to enlarge)

Approximately a 100% crop from the ISO 6400 image properly exposed (click to enlarge)

No noise reduction applied in camera nor in editing.

1/2500th sec. @ f/8; ISO 6400

ISO 200 underexposed by 5 stops, then brightened to match above in Lightroom 5.7.1. (click to enlarge)
There is a bit of "green" on the bricks that did not appear on the other image as well as a bit more contrast.
Any differences between the two should be able to be neutralized in an image editor.

On both tests, the intermediate ISOs show the same results as the extremes shown here. Both images are almost identical no matter what ISO you set as long as you have identical exposures.

From what I have seen from these brief, informal, non-scientific tests, I can only conclude that there is virtually no difference between properly exposing an image at a high ISO or keeping your ISO at 200, underexposing and subsequently brightening the image in your image editor.  This must reflect how Fujifilm has designed their system. That would explain the ability to process a raw file in-camera as many times as you like and lighten it, darken it, assign various film simulations, sharpness, tonality, etc.

I do wonder why I'm not seeing any of the telltale red/blue/green splotches of chrominance noise in the ISO 6400 files as well as the files that are underexposed by 5 full stops.  I didn't notice this until I compared these files with the same images from the same test for my Olympus E-M1.  I have to believe that Fujifilm is applying noise reduction to the raw files in the same manner that lens corrections are applied.  In either case, the user seems to have no control over the application of these adjustments.  Let me know if I've missed something.  I'm not particularly fond of the manufacturer applying adjustments to my raw files which I cannot control.  I would rather have the plain raw data and let me decide if and what I want to do with it according to my tastes and needs.

You decide if you reach the same conclusions as I have.  I'm sure there are some niggles in differences in conclusions, but overall, the images are very, very close.  I really don't think it makes much of a difference as to whether you set your camera to properly expose at, say,  ISO 3200, 800 or underexpose at ISO 200, then adjust the exposure in Lightroom or another image editor.  

So, don't worry about underexposing your images, go out and enjoy your gear and make some photographs!

I have performed the same tests for the Olympus E-M1 and will post those results in my next blog entry.  If you are interested, check back.

UPDATE:  You can find the E-M1 test and my conclusions here.

Thanks for looking.  Enjoy!

Dennis Mook

Many of my images can be found at www.dennismook.com.  Please pay it a visit.  I add new images regularly.  Thank you.


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