How can I approximate 'soft focus' digitally?

Question

In a previous question about soft lenses, it was suggested that much of the current practices regarding soft focus involve selectively soft focusing certain parts of the image and mattdm suggests its not as simple as a little blur.

What digital methods exists to give a selective approximate soft focus to photographs?

(I'm open to answers in Lightroom, Photoshop, and the GIMP.)

Answer

I think there's two separate parts to this; first, how to replicate the effect of a soft focus lens in software, and second, how to do what Jay notes in your other question is common practice in modern portrait photography: selective softening.

How to replicate soft focus due to spherical aberration

There's several techniques for this. First, here's a sample image (a photo of my daughter):

And here's that image with a simple gaussian blur.

_{Following the suggestion in the comment below, I've replaced the original examples with versions where I turned the sliders up a little higher than I had originally, so the effect is more apparent. It could be even more dramatic, but this is as un-timid as I could make myself go.}

I found a pretty decent tutorial for one approach here: Soft-Focus Emulation in Photoshop. In summary, the process is:

1. Create three layers, each a duplicate of your image.
2. Apply a light gaussian blur to the top layer, and set it to be mostly transparent.
3. Adjust the curves middle layer to be quite bright. Apply a much wider gaussian blur to this layer. Set this to "Overlay" blend mode. (Soft Light would probably also work.) And, set the opacity to mostly (but not all) solid. The tutorial uses adjustment in Adobe Photoshop for this, which is a nice approach for experimentation.
4. The linked tutorial doesn't say this, but I found that it's nice to make a final adjustment to curves to get the overall brightness back in line.

I found this technique to be a bit tedious in Gimp, due to the lack of adjustment layers; you end up recreating and destroying the middle layer over and over again as you work to get the right effect. Anyway, a sample result:

Another common technique:

1. make duplicate layer and apply a high-pass filter (as with sharpening, but with a moderately-high radius)
2. invert that layer, and choose Overlay or Soft Light blend mode.

This is a lot simpler, and produces nice looking results with many images, although I think it's less technically similar to what a soft focus lens does. Result:

And finally, a third simple technique based on Stan Rogers's answer. The steps here are based on Gimp; the actual details should be similar in Photoshop.

1. Create a duplicate layer.
2. Add a Layer Mask to that layer, based on a grayscale copy of the layer. Immediately apply the layer mask. This creates a layer where dark tones are more transparent but which is otherwise identical to the base layer. (There's probably a better way to do this... comments welcome.)
3. Apply a moderate gaussian blur to this layer. This creates the "ethereal halo" blur. Set the layer to Lighten Only blend mode, and adjust the layer opacity to taste. You can also leave it in the Normal blend mode for a different effect, or try Overlay or Soft Light.

Result:

For comparison, I think it's handy to open each of these in its own tab and flip back and forth: orig blur 1 2 3.

Selective Softening

For the second overall part to the question, I think generally a more simple approach is used, where one simply makes a blur layer and then erases the blur to varying degrees in areas where more sharpness is desired. (With no curves adjustment layer.) But that's not an area where I've done much work, since it doesn't fit with my own style and preferences.

However, since I wrote this answer, I've tried it a little bit, and can happily remport that yes, using one of the above approaches in combination with selective erasing might yields nicer final images than a simple blur layer. If you have an image where you really want to post-process for this effect and have it look good, that's probably the thing to do.

Huge Disclaimer

This isn't really my thing. I'm more comfortable with the play-with-a-soft-lens-see-what-it-gets me approach. (For example, I enjoy attempting portraits with a zone plate, even if I haven't really gotten great results yet.)

Check more discussion of this question.

How can I capture a really soft-looking baby portrait?

Question

What techniques/lenses/settings can be used to achieve really soft-looking photographs like this:

http://christieadamsphotography.com/blog/?p=2711

I've got an older Canon Rebel XT with a few relatively inexpensive lenses (50mm fixed, 28-135mm, and the kit lens).

I'm particularly interested in achieving the look where only the central features of the face are in focus and the other parts of the face and background are blurry.

Answer

You'll want a large aperture lens with a medium telephoto distance to replicate her photos. She lists her equipment in an interview and she appears to do a lot of her work with a 50mm f/1.4 and an 85mm f/1.8. Those are going to give you the look of the photographer you linked - in terms of the shallow depth of focus. But she is using a full frame camera, so you're going to have a tough time replicating her very shallow DoF shots on your cropped sensor Rebel.

If you're really digging her look and trying to replicate it - throw out any flash and artificial lighting - she's a natural light photographer. She bills herself as such and doesn't list any flash equipment among her equipment. She'll be using diffusing material or naturally diffuse light to create that soft light (soft light is the term for the long falloff off her shadows on the subjects). Think bed sheets, big windows with translucent blinds, cloudy days, shade from trees, etc. That soft look is a partly large aperture and partly soft light.

If she's doing Photoshop to make it softer (which it doesn't really look like she is much to me), you can try reducing clarity as @Steve Ross mentions or try one of the digital soft focus techniques here.

Baby photography (one of the big specialties of that particular photographer) is kind of a whole other world, so there's a bit more than just the right equipment. You'll need to be flexible, patient, have a plan - but be willing to adapt. Newborns have particularly splotchy skin so that's one reason you see alot of black and white there. Cute outfits and hats work to help 'deal' with some of their features that may not be quite in normal proportions yet.

Check more discussion of this question.