Fuji X-Trans ISO Noise vs Film Grain

― Terry PratchettHogfather

Photography 101: The Exposure Triangle

You know all about the exposure triangle right?  Exposure is determined by three factors the aperture of the lens, the shutter speed and how sensitive the film/sensor is.  Aperture and shutter speed are common to both film and digital cameras, they dictate the amount of light reaching the film/sensor.  The aperture is the size of the hole letting in the light, the shutter speed is how long the film/sensor is exposed to that light.  This is why doubling your aperture halves your shutter speed and vice versa – to achieve the same exposure.  The third side of the triangle is how sensitive to light your film/sensor is.

So we’ve reached the point where we have light hitting the sensor we just need to measure how much in order to generate an image of light and dark.  If you can make your sensor more sensitive then you can operate it in lower light or with a faster shutter speed/smaller aperture.  However, your sensor has a sweet spot known as the base ISO – on Fuji X Trans cameras that is ISO 200.  The only way to make the sensor more sensitive is to turn up the gain on the electronic photo detectors, that’s equivalent to turning up the volume on a quiet sound source, it gets louder but it gets distorted,  Signal to noise ratio worsens, that’s why we call it noise.

In a film camera the sensitivity is determined by the speed of the film stock referred to as ASA and equivalent to digital ISO.   In black and white film the blacks are clumps of silver halide that have reacted to light, the faster (more sensitive) you want the film to be larger those clumps have to be in order to react quickly.  The larger the clumps of silver halide the more coarse the grain of the film kind of like an analogue signal to noise ratio.  OK, it is somewhat more complicated than that, but without going into optical densities and logarithmic transmission co-efficiency you get the point.  Higher ASA/ISO mean more grain in the photo.  Reacting to light and going black? Yep that’s why the image is a negative.

So there really is an equivalence when it comes to digital noise and film grain they are both products of increased sensitivity.  The digital sensor has a huge advantage though, it has technology on its side.  Electronic photo detectors get smaller and smaller so megapixel counts rise, signal processing algorithms improve to filter out more of the noise.  Film is stuck with chemistry and physics and as a wise man once said, you cannae change the laws of physics.

How Much Have Things Improved?

Consider this picture of my wonderfully photogenic son.

Film image of a boy looking into the camera, image demonstrates a lot of grain/noise.
Nikon F100 and Nikon 50mm f/1.4 G at f/1.4 Ilford HP5 Plus 400ASA

This was taken using Ilford HP5 Plus ASA 400 film the blurb on the Ilford website says:

ILFORD HP5 PLUS is a high speed, fine grain, medium contrast black & white film making it an excellent choice for journalism, documentary, travel, sports, action and indoor available light photography.

Nominally rated at ISO 400, HP5 PLUS produces negatives of outstanding sharpness and fine grain under all lighting conditions.

Fine grain.  It says that twice.  Go on, really look at it, right click it and open it in new tab or window, pixel cluster of silver halide peep it.  I dare you.

Consider also this picture of my son taken more recently, he now rarely looks up from his iPad.  This is at ISO 4000 not 400 like the film image, we are talking more than 3 stops less light on an APS-C sized crop sensor not full frame 35mm.  Honestly, it really is ISO 4000, ask in the comments and I’ll send you the RAW file.

Boy in monochrome looking down at an iPad, image shows almost no noise
FujiFilm X-T1 1/110 Sec @ f/2.0 ISO 4000 (Fujifilm XF 35mm f/2)


Even pixel-peeping it is hard to see any noise on the properly exposed areas of his face and the noise in the shadows is very subtle.  There are orders of magnitude more detail in the digital image despite there being more than three times as much light available in the film image.  How far have we come?  A VERY long way.  We haven’t just come a long way since film was the only option we’ve also improved the quality of the noise in our images hugely since the early days of DSLRs.

The word “usable” pops up a lot in reviews and discussions about high ISO performance.

“Noise creeps in around ISO 1600 but images are usable even at ISO 6400”

Usable for what exactly?  Printing?  What proportion of your images have you ever printed?  Don’t get me wrong, I love printing my images and holding them in my hands.  You can appreciate and evaluate them in a completely different way compared to onscreen images.  But I have 35,000 images in my Lightroom catalog and I would estimate I have printed no more than 500 or so of them – that’s less than 1.5%.

What’s the Real Difference Between Noise and Grain?

The grain (or analog noise?) is random, but random in a distinctive way, so distinctive in fact that there are numerous places you can download grain maps of different film stocks to apply to your digital images.  I believe Fuji use three different grain maps in the in-camera Acros simulation amongst other dark magic and processing.  Making your digital images look like film is big business.  So people seem to want the grain but they don’t want the noise – remember all that “usable” stuff?

Does Noise Really Matter?

I would suggest it matters a lot less than people think, I actually like the noise in the digital image above, I routinely dial in ISO 4000 when I am shooting in monochrome on my X-T1 just to get that effect.  The film image is also a print about a metre high on my wall, so that one is definitely usable 🙂

There is precious little noise in images from X-Trans sensors but what noise there is can really serve to enhance the feel of an image, don’t be hating on the noise, think of it as digital grain and learn to love it.