High ISO Noise; My Secret To Minimizing It

This is the small test setup I constructed a few days ago to test how exposure affects digital noise
at high ISOs.  I tested my Fujifilm X-H2S, X-T5 and Nikon Z7II.  All of the files can be found,
full size, on my website, here. Read on for more details. (click to enlarge)
Fujifilm X-T5; 16-55mm f/2.8 lens @ 35mm; 1/10th sec. @ f/8; ISO 12,800 (overexposed by 2 stops)

In my last post, here, I asked the question, "Can we now take digital noise off the table when we are considering buying a camera?"  Since I brought up the topic of digital noise, I thought I would continue with the topic.  I have discovered the secret to minimizing digital noise at ISO 6400 and even ISO 12,800.  Maybe higher but I never expose with higher ISOs than those and almost never with ISO 12,800.  What is the secret?

In a word, "overexpose!"  If you can, if its possible with your subject, it is at all feasible, overexpose your high ISO image file to place your histogram as far to the right as you can.  We've called that 'expose to the right' or ETTR.  With moderate and low ISOs I no longer think ETTR is necessary but at high ISOs, it works wonders in reducing digital noise.

I know with some subjects pushing your exposure to the right might not be feasible, after all why are using such a high ISO, but if you can push your exposure at least one stop and sometimes even two stops over what your camera is recommending, digital noise will be greatly minimized.  More than you may realize.  Also, remember, your histogram is showing you a JPEG rendition of your exposure so when you think it is all the way to the right, you still have some latitude to not clip your highlights.

About a 100% crop from above showing the digital noise.  This was overexposed by 2 stops and
then corrected by moving the exposure slider to the left in Lightroom.  On my website, here,
I have uploaded all of the X-H2S, X-T5 and Z7II images, full size, unedited except with
minor corrections as described below, to illustrate my points in this post.   (click to enlarge)

What you never want to do when shooting with high ISOs is to have to brighten your image or move the exposure slider to the right when editing, in other words, you never want to underexpose it.  In fact, ideally you want to have an image that is too bright and you want to have to decrease brightness in Lightroom or another editing program.

If you have to brighten your image in your editing software or move the exposure slider to the right, you are, in effect, raising the ISO of your exposure.  For example, if you have your camera set for ISO 3200 and in Lightroom (or whatever you use) your image is a bit too dark and you move the exposure slider to the right to +2.0, what you have done effectively is raise your ISO to 12,800.  All that noise now appears.  Not just in the shadows, but everywhere.  Overexposing it, effectively lowers the ISO and the associated noise.

I currently use three different digital cameras.  My two primary cameras are the Fujifilm X-T5 and X-H2S.  My alternate camera is a Nikon Z7II.  The two Fujifilm cameras have the latest and greatest versions of sensors and image processors but the Nikon is a few years old now and Nikon has introduced a new sensor and new image processor.  So, the Z7II isn't the latest and greatest.  But that doesn't matter.  If you push your exposure as far right as you can, even noise in the older sensor cameras can be significantly reduced.  I am amazed at how well the X-T5 handles digital noise when I expose my files using ETTR.  An APS-C sensor with 40mp shouldn’t be this good.

One technique I use to make this easier, again it won't work with all subjects, is to turn on bracketing and make one exposure at the settings the camera recommends, one stop more than the camera picks and the third two stops more than the camera recommends.  Some cameras, including my three, will allow such bracketing sequences.  If you don’t want to set bracketing at one stop increments, try 1/2 stop increments and make 5 exposures.  In this way, you always have a choice if you accidentally clip your highlights with the brightest exposure.

On my website, here, you will see all of the test images I made the other day, with all three cameras, set at ISO 6400 and ISO 12800, showing normal exposures, underexposures and overexposures.  I renamed the files by which camera and what exposure was used.  That is in the lower left corner.  They are full sized JPEGs, unedited with the exception of a very minor white balance adjustment and normalizing the brightness if they were under or over exposed.  There has been no  additional noise reduction added in any of the image files, only the default color noise reduction that is applied by Adobe upon import.  No additional sharpening has been applied either.

Finally, all of this is not such a critical issue any longer as we have the new artificial intelligence (AI) based tools to reduce excessive noise while keeping the fine detail that previously was wiped out with aggressive noise reduction.  Still, the less noise the better the file.

This is a really good time to be a photographer, isn't it?

Join me over at my website, https://www.dennismook.com.  

Thanks for looking. Enjoy!  

Dennis A. Mook  

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