Archive for September, 2008

High ISO Black and White

Yesterday we got the remnants of hurricane gustav here in central illinois. It rained most of the day, and after dinner Lily, Lucy, and I decided to go for a walk in the rain.

Running in the rain

Running in the rain

I find myself gravitating towards grainy high contrast black and white pictures. There’s just something about them that I enjoy. Don’t get me wrong, I find the smooth tones of a well done monochrome wonderful as well (as in the latest Lens Work).

I’ve been noodling with an old Pentax K-1000 and some Ilford Super XP2 film lately. While I enjoy using the camera, the quick turn allure of digital is omnipresent. Plus, I did just get a new camera.

Greenway sign

Greenway Sign

So, off we went in the rain. It wasn’t raining very much. Just a sprinkle really. I had to push to ISO3200 equivalent just to be shooting at around 1/125, f4. But, the black and white conversions effectively hide the chroma noise, and I like the grain look of the luminance noise. I have not applied any noise reduction, but will probably end up trying that later this weekend.

Walking home after the rain

Walking Home After the Rain

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Please don’t feed the animals

We took the family up to Wisconsin to spend labor day with my wife’s family at the lake. Since I had my new toy, I wasn’t shy about taking pictures.

The kids went tubing, we had a mini-Olympics, and generally got to bum around with cousins.

My favorite picture of the weekend:

From Labor Day, 2008

Please don’t feed the animals

I’m sure they don’t mean us, right?

Also, the medal ceremony from one of our Olympic games:

From Labor Day, 2008

Medal winners

You can see one unhappy contestant, camera right. Eventually all the kids won a medal, I think.

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Reduce, reuse, recycle

Crumpled Cans

Crumpled Cans

Not too much going on today. I had hoped to make it out to Busey woods and see what I could find. But, mother nature had other plans for me. The heavens opened up and rain came down in torrents.

While warming my lunch I happened to see our can recycling box.

I’d like to think that this somehow speaks to positive recycling. The cans are sitting in a repurposed box, waiting to be recycled. But, I suppose that the darker message is that we’re using all of these natural resources and this is what it’s come to. Crumpled cans sitting in a used box.

Food for thought.

ADC response of a Canon 40D

This past Thursday I upgraded my camera. I had been shooting with a Canon Digital Rebel XT for the past two years, and while it’s served me well, I had an itch and decided to get the 40D.

While I was cruising around the web, drooling at different cameras, I ran into a web page (I can’t remember how I got there) that suggested a method to determine (in a somewhat crude fashion) the dynamic range of the sensor in a digital SLR.

The technique suggested is really simple. Using your fastest lens, take a picture of a neutral subject (white, grey, etc). Keep the aperture at wide open and set the shutter speed such that you are exposed as bright as possible without an overexposure warning. Then, keeping the same shutter speed, stop down by full stops. The histograms will show where the camera is digitizing the luminosity info from the sensor.

I did this for my new camera and found the results rather interesting. Note that the “highlight tone priority” was turned off, and ISO 100 was used for all exposures.


Composite histogram for exposures with an aperture ranging from f/32 to f/2.8

The sensor / ADC is not linear.

If it were linear, then you would see (within whatever standard deviation) a histogram value step down by half for every stop of down of the aperture.

The histogram counts for the given aperture values:
(F-stop :: Histogram Median)

f/32  :: 7
f/22  :: 15
f/16  :: 31
f/11  :: 55
f/8   :: 109
f/5.6 :: 153
f/4.0 :: 206
f/2.8 :: 241

While the first few lower entries appear to be linear, the higher values are decidedly not.

Using Excel, I plotted the median values and then did a trend line to approximate the type of curve that would best fit these results.

Picture 1.png

Curve fit of the observed histogram median results

While the curve fit shows a power based curve seems to fit, it sort of appears to be two different linear lines to me. But, it’s hard to say just looking at it.

Certainly from a technical standpoint, there’s no reason why the ADC has to be linear. While most are linear, having programmable reference levels wouldn’t be that hard to do.

My conclusion: I’m not sure. I believe that the composite histogram itself is telling. The “Expose To The Right” idea does not seem to be correct. The original idea was that the linear ADC (sensor + ADC, of course) would mean that after the highlights, you would immediately lose half the information. The histogram seems to say otherwise.

Does this mean that the end results from the ETTR are bunk? Probably not. But, it does seem to indicate that there isn’t nearly as much to be gained from the approach of controlled over-exposure.

Though I have not collated results for the “highlight tone priority,” I can say that there seems to be a shifting of the “sample points” from these results.

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