Thursday, June 2, 2011

Ex. 24 Sharpening for Print

Sharpening has been a process I have wrestled with since I first started dabbling with Digital Photography.  My early cameras were typically 3-5MP (my first was VGA! -1024x780 = 0.8MP) and had pretty basic optics.  At the time the images were still considered very good and a big improvement of film based point and shoot, however, sharpness left a lot to be desired.  As a result I found myself doing two things to the images, first applying an overwhelming amount of contrast and secondly over sharpening.  This created punchy, but not terribly refined images.

As time has passed I have backed away from this stance, looking for a more refined finish to images. Two things have helped in this process, the first is the improvement in workflow tools, with much better control over sharpening, in my case I use Lightroom and find the sharpening tool more than sufficient for my needs.  Secondly my cameras and particularly optics have improved.  My latest DSLR, the 21MP Canon 5D Mark II coupled with a high quality prime lens produces images that are pretty much Pixel sharp out of the camera.  Of course this requires careful control at shooting to avoid Dof blurring or diffraction, caused by too low or too high an aperture.  However, the result is that I use far less sharpening in my final output, placing greater reliance on careful management of contrast and colour to emphasize detail in images.

Sharpening, does have a use, in particular when preparing images for web.  In this case I frequently use the sharpening option in the Export dialog of Lightroom.  This is not necessarily the most accurate, however, for large numbers of images where I am not attempting to achieve the ultimate quality I find it more than adequate.  As the text suggests, the degree and refinement of sharpening depends on where the image is headed, for Flickr defaults are fine, for an A3+ print headed for the gallery wall I would be far more circumspect.

The subject also influence sharpening, a portrait needs far greater care and management of the process to avoid adding graininess to the skin when trying to sharpen hair detail. An underwater image of a spiny creature is completely different and can have a far greater application of sharpening, indeed it probably needs it.  Water softens images.

Turning to this exercise, as suggested I have selected a portrait as the target for the sharpening:

This image combines hair detail, eye detail, skin and large amounts of negative space, hopefully a good candidate for the tests.   The image was captured using a 135mm prime lens set at f/8 and using studio lighting.

First of all I have imported the image into Lightroom and applied a number of contrast and colour adjustments.  I have then made 4 virtual copies of the image and applied differing degrees of sharpening.  As with most advanced editing tools Lightroom offers many parameters to the sharpening process, creating a 4-dimensional space of possible options.

To keep things things simple I have left all settings at the default and simply used the "Amount" slider to change the degree of sharpening, setting it to 0, 50, 100, and 150, spanning the full range of adjustment.  When sharpening an image for final output I would also adjust the Noise Reduction and masking to avoid graininess in the image.  As such this is a very simple approach to sharpening, but should serve to illustrate the different impact of sharpening settings.

After adjusting the images in Lightroom, I exported them as 16 bit Tiffs and loafed them into CS4 for printing.  At this stage I enlarged each to 100% and took screen grabs of the area around the eyes to allow a comparison of the impact on the screen:





The unsharpened image is visibly softer than the image with 50 set as the amount of sharpening.  At 100 the sharpening is starting to become too strong and is creating too much texture in skin, at 150 this effect is quite unpleasant.  Another affect of sharpening beyond 50 is a progressive lightening of the hair as the tool creates greater light-dark contrast.  This was not an expected effect for me, but is logical once I think about it.  It is interesting that the sharpening tool can also impact the contrast and colour of the image, food for thought.

Moving now to printed versions, the first question is what a full size print is.  This ambiguity is not untypical of the text in the course manual, but is not a problem.  I have printed two sets of images, the first a group of 4 prints on a single A4 sheet, so roughly 15x10 cm, and then 4 individual full size A4 prints.  I could have printed up to A3+, but that would have been both expensive and probably pointless.

First of all the print size makes a big difference, the 10x15cm prints exhibit very little difference, without knowing in advance which were sharpened I would struggle to know which is which.  At A4 there is a visible difference in the prints and again I find the lower sharpening setting of 50 to be the most satisfying visually.

What have I learned from this?  First of all the degree of sharpening very much depends on the size of the print, a small 10x15cm print cannot resolve much detail in any case, whilst an A4 print allows much closer inspection, A3 would be even less forgiving. I do not think this is a question of screen versus print, but a question of at what resolving power will the photograph be examined.  Factors outside the photographers control such as from what distance the image will be viewed will affect the apparent sharpness of the image. 

Secondly when working with a portrait the amount of sharpening must be very carefully managed, too much and the skin can lose its smooth quality, however, use of the other sharpening parameters such as Masking can mitigate this, as can use of the noise management tools.

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