Saturday, October 2, 2010

F300EXR – Review Part 19 – Smearing test part 1

Smearing is something the new Fujis do quite aggressively. The EXR cams do it with abandon when shot at L size, but it is much rare at M size … still, you can stimulate it by reducing contrast until the camera thinks it is looking at noise. Then it will smooth away all the detail for you …

How can you reduce contrast?

  1. Shoot things from further away … the smaller the details, the less they look like details and the more they look like grain (noise)
  2. Shoot things with uniform colors … contrast requires a change in tone or color
  3. Shoot in low light or soft light … contrast increases as light increases (ever try to read something in near dark?)
  4. Underexpose … if you deliberately or accidentally allow less light to the sensor, the camera will see less contrast
  5. Increase ISO …. the noise injected into the image tends to reduce the contrast of the actual data

There are probably other ways to reduce contrast, but these are the obvious ones. So, the corollaries are probably worth noting. I.e. how do you increase contrast and thus the crispness of your images?

  1. Get close. The HS10 smears like mad from a distance … but fill the frame and things start to look nice.
  2. Shoot subjects with inherent contrast.
  3. Increase light. Add light (flash) if you have to. (Note: At some point too much light makes things look harsh, as with midday sunlight.)
  4. Expose to the right, but don’t overexpose because that tends to lower contrast in the highlights :-\
  5. Decrease ISO … keep noise at bay

I decided to run a test that would attempt to simulate a low contrast subject at distance and simultaneously show the effect of underexposure.

First, I tried the infamous Jamaican dollar test. Show from 15 feet in low light.

0 EV

DSCF0221_0ev[1] -1.33 EV


The difference is pretty obvious, although less so on my out of whack TN panel. Obviously, details like the dark area around the head become almost uniform to the eye … but the question is when they become uniform to Fuji’s noise reduction algorithms?

Here is a set of crops … the left side is a set of exposures of increasing underexposure and the right side is the same crops equalized in exposure by dialing exposure up in ACR6. Click through for full sized 100% crops.


One side effect that I was not aware of is that the contrast increases in the adjusted crops. Pulling up an image from a severe underexposure results in a harsher image than you get by exposing properly. This could make a real difference in the quality of the iage, further strengthening the argument for getting the exposure right … learn your meter!

The main observation with these is that the low contrast detail, which includes the area surrounding Sir Bustamante’s head and the almost white flower petals, is compromised pretty badly by the time we reach the –1.33 EV underexposure. Edges of higher contrast detail – BANK OF and ONE D are good examples – are also looking a little compromised.

Obviously, these details are pretty small … but imagine them repeated across the frame as a field of like-colored foliage or lots of repeated edges. They would become noticeable as being rather degraded. I think that’s a bit of what we see every day in images posted to the Fuji forum.

The bill test leaves something to be desired though. Even the low contrast details are pretty large, so how about we try something a little different. The paint brush test seemed like a good idea. I happened to have three paint brushes lying around, so off I went.

Here is the 0EV image

DSCF0227_0ev_OOC[1] Click through to see the superb details in this one. But even here at 100 ISO we can see some compromise in the tips of the brush on the right. EVen though there are individual strands there, they are the same color and contrast is not very high so they are starting to bunch up. This is a classic issues with Fuji cameras and hair … or fields of foliage from a distance.

Here is what –2EV looks like


Here is what –2EV looks like when equalized to 0EV

DSCF0233_2ev_equalized[1] That’s surprisingly good. There is more latitude than you think in these little EXR cameras. But the areas where colors are similar are actually under attack here. And ISO as at base, so there is nowhere to go but down.

The crops again …


It is obvious even at the 400px wide blog version that things are deteriorating as the underexposure gets more severe. But it is hard to see the extent of the smearing from the crops presented this way. So here is a set of three crops … 0EV in the middle, –1EV on top and –2EV on the bottom. All equalized to 0EV … and what we see is that there is definitely smearing of the areas where contrast is low to start with. So apply this to any foliage shot where the light is low and you can start to imagine what will happen …


Again, you must click through to the larger version to really see the effects of underexposure.

Bottom Line

A little underexposure is safe … and even warranted when you want to saturate colors a little more. But if you underexpose by 1 or more stops, you are going to see a lot of extra shadow noise (see the final image above) and a lot of extra noise reduction destruction …

I will repeat one of my primary suggestions for learning to nail exposures here: read John Shaw’s Field Guide to Nature Photography …

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