Challenge

Challenge #1

Lesson/Challenge/Puzzle Number One: A Big Deal

Digital Photography is not like film photography, except that plenty of people shoot film and immediately digitize it so they can play with it in digital form. The lenses, f-stops and ISO notions are common to all photography, so those don't count in this challenge either.

Your task is to rebel against the status quo and discover what the puzzle is all about. Once that is done, the practical result of it will join your growing digital photographic awareness in a very useful way. Then the challenge will be this: "Do I use the new found information or not? Or perhaps only use the knowledge at certain times?"

The resolution to this is not earth shattering, but it's not a calm walk in the park, either. You'll know when you know. But the Lesson/Challenge/Puzzle/Test is named aptly and the result of knowing its secret may help you immensely when the chips are down.

What's really going on with the images below? Roll your mouse over the images and some form of change will happen. Not all changes are the same, but all are related.

The question is this: What, exactly and precisely, is the root difference between example 1 (no mouse over) and example 2 (mouse over) in these shots?

Each shot is cropped directly out of a two layer stack of imagery and presented here for examination at full scale from that stack.

Crop #1:

Of course, you can see shadow movement between layers, showing that these are from two images shot at slightly different moments and you can see that the color and tonality differences between the two are microscopic, suggesting close, if not identical exposures.

Subtle other differences are in the images, too, but what do they imply?

Crop #2:

By now you might have guessed that these are crops out of the same image, eh? In fact, they are. The Digital Rebel at an optimum f-stop has enough depth of field to pack things from sixty feet to infinity, even when working at maximum zoom. And again, motion from shot to shot reveals that time has passed between images. But it was only a few seconds. Shadows like the telephone pole on the roof show that. So what big, hairy difference could there be between these two shots? Compression? Nope.

Crop #3:

Lots of motion here, but very little extra real clue. Detail in the upper left is consistent from shot to shot and although some leaves seem sharper than others, the mystery deepens. You will, no doubt, run through all the usual suspects and come up empty.

Follow up question: The images below show a far more major difference. It's due to a similar, but not exact-same condition that exists above. If you can truly see what the difference between these shots is, it may help you define what the difference between the shots above is.

Crop #4:

This site is not known widely to the digital photography community. It's a new thing, just a baby. So before we get to Lesson #2, we'll let this one sink in for a while.

In January, 2004, the answer will be given. If you think you really, really know what the answer(s) is to the above puzzle, drop me a line. Perhaps you will be among the list of those whose ability to see, analyze and define with digital clarity.

Honestly, if I hadn't dreamed up this puzzle/challenge/lesson, I don't know what my own reaction to it would have been. Good luck.

--Peter iNova (peter.inova@mac.com)

Answers, already

Ready? Sure you are. And now for the Big Revelation: The top three crops are from the same frame, but of course a second frame is revealed in the rollover. The difference between the frames is...

Here's what the difference is NOT: Not a difference in compression, f-stop, ISO, focus, sharpening, contrast, colorimetry or RAW vs. Compressed. It's the same lens, the same camera and the same exposure in each. The clue should be "Notice how different they are NOT." Because differences are minor. About the same amount of difference between shooting the scene at f/5.6 and f/11 as far as sharpness goes, but that can't be IT because the f-stop was the same for both shots.

The Big Difference was this: One was shot at Full frame size, 3072 x 2048 pixels large, while the other was shot at Medium frame size (2048 x 1360 pixels) and enlarged in Photoshop up to the size of the full frame. Bicubic interpolation was used, but no post-enlargement sharpening was added to the one labeled Crop #2 and only a tiny amount of Unsharp Masking was added to Crop #1 and Crop #3. This showed up as 0.3 pixels at 87%, for those of you who use Photoshop's Unsharp Mask tool. Just a tiny tweak to the finest contours without introducing artifacts.

What's the point of all this? It should be obvious by now, especially when you consider how LITTLE extra you get out of shooting with the largest frame size. Don't get me wrong, you do in fact get something extra with that biggest frame option, namely the maximum detail, but if you shoot that large frame at f/5.6 or f/16 and higher, you've lost all your advantages. Your picture will be "diffraction limited" and there's no way you're getting more detail onto that chip when the lens has been prevented from resolving more detail by Ma Nature and her cup of Physics.

One Big Benefit from shooting with the Medium frame size is this: you get to store about 50% more images per megabyte on your CF card. Meaning that your card goes farther and you get more opportunities to find that perfect shot. Photography is a game of moments, if you think of it that way, and the more moments you collect, the better your chances of bagging the Big One that Didn't Get Away. Or POTD*, whichever comes first.

Crop #4

About that fourth shot. I cheated. Just to throw you off--and to make things more interesting--it's a same-size, pixel for pixel comparison between a Nikon Coolpix 5700 (a 5-megapixel camera) and the Rebel with the Kit lens. After much wrangling, the same size image was forced to cover the same pixel count with both cameras so you could see directly how much detail each format of lens/chip acquires per pixel. But I think I'd have to repeat this test a few times to draw major conclusions. Both cameras were on tripods, both were shot at ISO 100 set for Daylight white balance. The crop here is at 100% so we would expect a certain amount of softness. The Nikon image (slightly darker/bluer and seen only with the mouse rolled over the frame) seems to reveal a bit of camera movement, and that's possible since the tripod was a lightweight and the camera was tripped manually.

What's it tell us? By and large the conclusions seem to be this: Canon is getting a LOT out of every pixel. More color differentiation, longer tonal scale and lower noise. Apparently more detail, too. And with 512 more pixels in the image width, same-size images from the DR would be 20% more detailed on a same-size print, all things being equal, but with perhaps 30% more native detail per pixel, that might actually show up as around 50% more detail than the very capable 5-megapixel capture.

Not science, just experience. Anyhow, I'm enjoying this camera A Lot.

-iNova (January 15, 2004)

*POTD is Picture Of The Day in many web contests.

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