Bruce Fraser wrote about the perils of using 100% zoom for capture sharpening photographs. I've written about it, too, in my eBook on sharpening. I've also written about the perils of using 100% zoom for judging noise reduction.

Thinking about the proper zoom for sharpening has evolved over the years. A few years ago, the recommendation was to use 100% zoom. I even had a tip way back when making that recommendation.

Lightroom and Adobe Camera Raw require 100% zoom to view sharpening effects. Now you see many Photoshop notables arguing again for 100% zoom. Jeff Schewe says, if only Bruce fraser has lived longer, he'd agree, too. (Now that Pixel Genius algorithms are used in Lightroom and ACR, of course he does.)

I'd like to invite readers to help educate me. I understand the logic of Bruce Fraser. I'll set it out briefly below.

I remain skeptical of 100% zoom. I haven't seen a compelling case yet for using it. Maybe someone will persuade me that 100% zoom is the proper zoom for judging sharpening. I've been reluctant to sharpen in Lightroom or ACR because they force me to use 100% zoom (or higher).

The Case Against 100% Zoom, Briefly

100% zoom seems like the natural choice for viewing a photograph. Photoshop calls this Actual Pixels.

The problem is that very few monitors have the resolution of the typical inkjet printer, let alone the resolution of images from recent generation DSLRs. If you map each single pixel in a digital photo 1:1 to pixels on a monitor, what you see is an enlargement on your monitor. Use an image from a full frame 35mm camera or a medium format digital back and the photograph is poster-size when viewed on a monitor. This is sure to distort perceptions of sharpness and noise. This is why Bruce Fraser (and others, like Jeff Schewe) argued for a zoom that was closer to intended output size: something like 50% or 25% or maybe even 12.5%.

What you have to be careful about is anti-aliasing effects. Anti-aliasing softens parts of an image to reduce the appearance of jagginess. The recommendation was to use a zoom ratio that combined pixels in even multiples to reduce ant-aliasing and left the photo enlarged at close to the intended output size. For example, a 50% zoom was better than selecting Fit Screen, which might give you a weird zoom and more anti-aliasing artifacts.

The Case For 100% Zoom, Briefly

I have yet to read a solid defense of 100% zoom. I'm a political scientist by training, and we study power (which we define in terms of influence). Adobe has a lot of influence over the digital photography community. It has even more influence over the Photoshop gurus who want to appear at Photoshop World, write for Adobe Press, etc. So it doesn't surprise me that most gurus have already adopted a 100% zoom mantra now that it is required for Lightroom and ACR.

There are advantages to capture sharpening in Lightroom or ACR. These are disadvantages, too. That's a discussion for a different blog entry, however.

What I have not yet read is a solid, logical argument in favor of 100% zoom. The closest I've seem is bluster from Jeff Schewe in a recent thread on Photo.net. He argued that almost everyone now uses digital monitors and they can be used at 100% zoom for sharpening.

I don't know what pollling firm Jeff uses. I am extremely suspicious about the claim that nearly everyone uses a digital monitor. There are still lots of CRTs out there. And digital monitors are not all created equal, either.

I'll take a stab at making a fair argument for 100% zoom and then I'll wait for reader feedback to help me think this through.

First, do not equate CRT = analog and LCD = digital. Many LCD monitor users, perhaps most, use an analog connection from their video card to connect their monitor. Yes, an LCD monitor is a digital device. But, when you use an older video card and an analog connection, you get distortions from the conversion of analog signals to digital. If your LCD monitor has a digital connection, you'll still need a graphics card that has a DVI-I or DVI-D connector and a DVI cable (many LCD monitors come with only an analog cable).

A digital monitor coupled properly to a digital video card will produce sharper images. No question.

1:1 pixel mapping is available on some LCD monitors. It matches the resolution set on a video card to the screen resolution. Each pixel of the video signal is mapped to a single corresponding pixel on the LCD screen. This produces the sharpest possible picture for display. The image is not stretched and distorted by the monitor. This is great for images intended for  the monitor or a Web browser, but is not really a help for judging sharpening or noise reduction for other output devices. If your video card is set for 1,280x720, for example, and the LCD is set to 1,280x800, you're covered with an LCD that supports 1:1 pixel mapping.

Current generation video cards and graphics processors have better capabilities for anti-aliasing. No question. That means more sharpness and fewer artifacts, even with weird zooms.

The problem that remains is the mismatch between the size of the image on the monitor and the size it will appear when it is output.

Let's keep the discussion simple and assume printed output is intended. Let's assume a high resolution fine art print is intended. 300 pixels per inch.

There are monitors capable of 300 ppi. Very few of them. Very expensive. Certainly, most of the LCD monitors out there being used by digital photographers do not approach 300 ppi. Most don't even approach 200 ppi. So, we return to the issue of enlargement. What you see on your monitor is magnified.

The idea behind capture sharpening is to restore the sharpness lost during digital capture. It has to be soft. Sharpening effects compound. If capture sharpening produces any visible halos or crunchiness, you can expect scary artifacts after you apply output sharpening.

An enlargement is going to magnify the sharpening halos. They're going to be more apparent to they eye. From one perspective, this could be helpful. If you want to avoid even the hint of a visible sharpening halo, grossly magnify the image and look for it.

From another perspective, however, you run the risk of under-sharpening. Evidence of a sharpening halo beginning to be apparent in an extreme enlargment might not be detectable at output size. So, if you pull back on the sharpening because of what you're seeing at 100% zoom, you might be leaving image details softer than you otherwise might.

Most digital images have far more resolution than inkjet printers can resolve. Consider, for example, a Canon 1Ds MkIII image. 5616 x 3744 pixels packed in approximately 1 1/2 x 1 inch. That more than 12x the resolution of an inkjet print at 300 ppi and more like 25-30x the resolution of most of the monitors out there, even prosumer digital monitors.

What the Future Likely Holds

Photoshop gurus tend to work with the latest gear. I suspect that many generalize from their own experience and write for other gurus. In other words, for people who also use the latest video cards and video monitors.

Maybe my viewpoint is distorted and I'm the one who is generalizing from my own experience. I'm assuming that most digital photograhers are using monitors that have resolution that is a fraction of what a typical inkjet printer can handle and their video card is a couple of years old

It appears to me that Lightroom and ACR are engineered for display capabilities that are just now emerging. That's a smart choice form a software engineering POV and from a marketing POV. Better to be able to handle cutting-edge technology than disappoint the gurus and very few who already working with emerging technologies.

The digital photography community is broad. There are digital photographers who invest thousands in the best gear and continually replace it with emerging technology. But there are also a lot of photographers out there who are using gear that's several years old. Advice about whether 100% zoom is appropriate will depend on what sort of gear is being used to process the digital photos.

What Do You Think?

I'm still missing the compelling, logical case for 100% zoom in Lightroom and ACR. Feel free to agree. Feel free to make the case for 100% zoom. If the Photoshop gurus are too busy making videos to show off sexy new Photoshop CS4 features like content-aware scaling, let's see if we can think this through together. Go ahead and have at the comment system! :)

Cheers,

Mitch

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