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Wednesday, March 08, 2006

Pixels Aren't Just Pixels

by Paul Butzi

Regarding Mike's post "How Many Pixels Do You Need," I agree, but...I disagree.

It is not true that resampling simply "throws away" data, such that a 12mp image resampled to a 6mp image is essentially what you’d get if you had used a 6mp camera to start with.

This is because:

1. When you resample, you can make judgments about what data to preserve. One such judgment is feature preservation—the difference between resampling with "bicubic" and with "bicubic sharper" in Photoshop. That is, it’s possible to preserve detail in the lower rez image which would have fallen below the resolution of the 6mp camera, but was detected with the 12mp camera, and then preserved when the image was resampled.

2. When you resample, you are effectively oversampling the signal. Oversampling allows you to merge multiple samples into a single value—and this has the effect of reducing noise. As a rule of thumb, doubling the sampling rate reduces noise by a factor of the square root of two.

In other words, not all pixels are created equal. An image resampled from a Phase One P45 to the same pixel count as an image that was captured with a 6mp camera will contain more information and less noise, because although the number of pixels are the same, the image from the P45 has higher quality pixels.

In any case, on the larger issue, I agree—enough is enough. I have a friend who’s been doing very strong work with his 6mp Nikon, printing it on his Epson 2200. I swapped him two prints for two prints—getting the better end of the deal as usual. I put those two prints up in the room where I exercise, and I looked at them darn near every day, and they’re half of what convinced me to go ahead and buy an EOS 5D. The prints are roughly 10x15 inches, and they are luscious.

I make large prints, and for a great deal of the work I am now doing, the increased flexibility and speed of use of the EOS 5D I bought last November outweighs the advantage that my Linhof Technikardan 45s has in resolution. The 5D has defects (all of the work I am doing now is essentially landscape work on a tripod, and the camera has some unfortunate design features that make using it on a tripod at or above eye level a hassle), but so far in my life there have been three cameras that lit my brain on fire—the Linhof TK45s, the Leica M6, and the 5D. The rendering of the 5D is so noise-free, with such incredible smoothness and lush tonality…the first work I did with it when I got it was B&W (shot raw, converted to B&W in PS) and I thought I’d died and gone to heaven.

Posted by PAUL BUTZI


Anonymous Wilhelm said...

Subject: 100 year old Live Oak tree in Myakka State Park. Shot 10-15 years ago with the best quality Leica equipment, Panatomic-X film (ISO=32), printed 16x20 with Leica V-35 enlarger onto Agfa Portriga Rapid paper. (Obviously a slight crop required from the 2:3 format).

Same tree shot yesterday from virtually identical viewpoint, same month of year, both shot in mid-afternoon. Olympus E20 @ISO=80, f4.0, camera set to SHQ quality and default (medium) sharpness and contrast. Converted to B&W in PS Elements 2, cropped to match the old image (final image size 4.1 MP), printed on HP 7960 (only prints letter size, so I printed the digital file in four 8x10 segments to match the 16x20 silver print) at 600 dpi onto HP Premium Plus paper. Slight adjustments to contrast and brightness, but no additional sharpening applied.

Result: virtually equal sharpness and visible detail between the digital and the silver prints, when viewed from 12 inches. No "grain" or "noise" visible in either print.

CONCLUSION -- it only takes 4/5 MP to match 35mm maximum quality B&W prints.

7:01 PM  
Anonymous Anonymous said...

But I still want a 20x24 print (of fine landscape detail) of the same quality that I can get from 4x5 film. A 5D or a 1Ds2 won't do it. And I don't want to spend $40k on a P45 + camera. So I still need more (and cheaper) pixels.

In fact, I'd really like to get the quality that I could get of a contact print from an 8x10 neg. We are not yet even close to that!

Josiah Davidson

11:47 PM  
Blogger Joe Henry said...

Concerning the 5D and tripods...check out Really Right Stuff. I have an XPan and their L- bracket tripod mounts are a joy to use.

5:50 AM  

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