Depth of Field Bluring

Whilst digital brings many benefits to image making, control of depth of field is not one of them. Driven on by the consumer demand for high range zooms, an ISO around 200 and a small chip (in most instances) we find ourselves with poor ability to lose backgrounds in a portrait setting. A subject stands out before a blurred background and wide aperture telephoto lenses have frequently been used to great effect. At this point Photoshop CS comes to the rescue and we show here a quickie method of losing your backgrounds from Dave Simm and the use of the Lens Blur Filter from Mike McNamee.

SIMMply speaking - Soft Focus Background

The other day I was looking at a portrait I had just shot and thought, "I'd like to see that background a bit softer looking", then my mind went back to an article I wrote two years ago on that very subject; and there I sat, mulling over in my mind.... "make two duplicate layers, select the middle one, now make a selection round the subject, create a layer mask for the selection and......" Whoa: hold on there, this is Dave Simm, two years down the road and a lot more Photoshop savvy than when he wrote that one... As good as that method was, it was just too involved and labour intensive for quick fixes.There just has to be an easier way.

Adobe Photoshop

Well of course there is and it is just so simple I could have kicked myself for not thinking about it two years ago. As much as I love reading what the Photoshop Gurus would do, there is no way I can figure out their reasoning for wanting to find the hardest way to achieve a very simple result. I don't want to fiddle about with the extraction tool, or the magnetic lasso if I don't have to, so here is how I would perform that task now.

Just as with anything you do in Photoshop, you duplicate the image by dragging the thumbnail down to the "create new layer" icon; with the top layer active go to Filters> Blur> Gaussian Blur and blur the whole image to the level of softness that you want in the background.When the background is sufficiently out of focus click OK to accept the changes.

Photoshop Filter

Now select the eraser and its brush size and edge softness. With a bit of trial and error you can find a value so that you can get round the detail that you wish to be sharp. Stay on the top layer (the out of focus one) and start to erase only the subjects; this lets the bottom layer, which hasn't been affected by the Gaussian Blur, show through.

If you click on the eye next to the background layer, you can see the effect of erasing your subjects from background copy, click the eye again and you will see your new selective focus portrait. Now just before printing, flatten the image, colour correct, add Unsharp mask and save as: with a new name or number.

Photoshop Erase

That's it; that is all you have to do to create a great looking portrait with differential focussing the subjects are nice and crisp, while the background is soft and fuzzy, giving the image an almost three dimensional look. Let me just point out, that this image was wanted for Christmas Cards, which we sell at package prices, i.e. although there is a profit, I don't want it eaten up by computer time manipulating the image. I view greeting cards as add-on sales, which we might never sell if they weren't competitive.

When the client orders an image of 20 x 16" or larger, I may take a closer and perhaps revisit the method I described in paragraph one, but for quick fixes on Christmas cards, wedding candids or any other smaller print application, I don't think you can beat this one.

Final Picture

Photoshop CS Lens Blur

This is a new, sophisticated filter, which mimics the effect created by different types of lenses and lens constructions. There is a difference between true blurring due to depth of field effects and simply slamming in a bunch of Gaussian Blur. De-focussing blur varies around the focal plane, rising more quickly toward the lens and less so as you move away into the distance. The shape of off-axis flare spots mimics the shape and number of petals off a lens aperture diaphragm; the curvature of the blades affects the quality of the out of focus blur spot. Gaussian Blur tends to dull the highlights by mashing the darker pixels with the lighter ones. Lens makers such as Nikon (with its defocusing Portrait lens the AF DC 105 f/2) and Hasselblad (with their Softars) have always recognised the subtleties of blurring by proving these lens with controlled ways of destroying their sharpness. Before and After

For our example we take a recently published image of a triathlete. Note on the original that the triangular road sign and bus stop legend are legible.The shot was taken at 70mm focal length (zoom lens), at the full aperture of f4.5, on a Nikon D70.The depth of field could do with being a little shallower to create more impact than the restricted aperture could provide. The procedure for making an accurate simulation of shallow depth of field is described below and would apply to most other shots composed in a similar way e.g. a bride walking up a path.

1. The athlete was outlined using the magnetic Lasso Tool [1].This was quite a good cut-out but a little ragged in places, so it was adjusted in Quick Mask mode. [2,3,4].The more accurate selection was then saved as an alpha channel and named "Athlete Sharp Mask" (because it was sharp and hard edged).

Example

2. The Athlete Sharp Mask was duplicated and blurred

3 pixels using Gaussian Blur. This alpha channel was then named Athlete Blurred Mask. This procedure was to provide a more gradual transition between blurred and original image, later on. 3. Now a gradient mask is required which mimics the intensity of sharpness fall off either side of the focal plane - in other words the mask needs to be fully protective (i.e. solid black) around the athlete, but fall away to the front and behind i.e. the mask gradually feathers from black to white (a white mask equals a transparent mask). To do this the Gradient Editor is activated and set up as shown [5] i.e. 90% dense on the extreme left, 100% dense at 14% from the left; then gradually transitioned to clear (white) at the right hand side. Positioning of the controls is a bit of a guess. The rectangle "with a roof" controls the density of a point and the diamond slider controls the location of the mid point of the mix between the density points. The change of blurring as you move away from the plane of focus is hugely complex, depending upon the usual culprits like aperture, focal length, and format to which must be added the shape of the residual lens aberrations and even the shape and quality of the aperture stop itself (which is where we came in, with the Softar!). In truth, as long as the blurring increase gradually, the observer will be fooled, especially if the masking is accurate around the main subject. Once the gradient tool is set up, a linear gradient is dragged from the bottom to the top of the image [6] on a new Alpha Channel 1.

4. The "contents" of the Athlete Blurred Mask are now added to Alpha Channel 1.This is done by Ctrl-clicking Athlete Blurred Mask (in the Channels Palette) to load it onto Alpha Channel 1 [7]. It is then filled with black [8]. Later this will completely protect the athlete from the effects of the lens blur filter. This Alpha Cannel 1 is then renamed "Composite Mask".

5. The Lens Blur Filter is activated (Filter>Blur>Lens Blur) and then the "Composite Mask" is selected to provide the depth map [9].

6. There are many refinements to be made for absolute realism. For example the barriers by the athlete's left hand should be sharp, but the background behind them should be blurred. We made this refinement by adding a black shape of the barriers to the "Composite Mask", renaming it "Composite Mask REFINED" and then selected that to provide the depth map. Note that although this portion of the mask is quite crude it is adequate for the job [10].

Postscript

If you are now confused by the two options set out in this feature, lets Simmplify for you. If it is a quicky for a card, the web or a small image, go for the Dave Simm method. If you are looking for an advertising image, a portfolio image or a competition entry, the 20 minutes to do the job using graduated masks is well worthwhile. Your other option is to buy that 85mm f1.8 jobbie you always hankered after as a youth!

We have not described all of the settings in the Lens Blur dialogue. These change the shape of out of focus iris flare spots, number of blades and curvature. If you make a gradient on an alpha channel and then click on the image the Blur Focal Distance is activated and the blurring is adjusted around that point. You can control the dulling of highlights by dropping the Threshold and altering the Brightness to taste. Finally you can add back noise to overcome the smoothing of the blur filter (which can make the image look a little unreal if left without noise). The Photoshop Help file is vague on this topic but for registered users the Adobe studio web site (studio.adobe.com) provides additional guidance. We found little help in any of the manuals and books at our disposal. Overall the technique we described above, which does not use all the whistles and bells, seems the best approach!

Example

Photoshop

Photo Quote: It is my intention to present - through the medium of photography - intuitive observations of the natural world which may have meaning to the spectators. - Ansel Adams