There are many reasons why a photographer or retoucher might need to use a "skin smoothing," technique; reasons that range from a breakout in the days before a wedding, to shooting a beauty image for a cosmetics company.
Skin smoothing is a huge topic, and there are countless different approaches with different reasons behind why people choose a certain approach, but for the purpose of this blog post I'm going to start at the very beginning, and the explain the most popular/currently well known techniques and why a photographer might choose to use them.
Great looking skin on camera starts with the right light. The most flattering light for skin is even, diffuse light.
Because shadow gives shape and directional light will show both the highlight and a shadow of each pore, blemish, scar or wrinkle, thereby making the texture apparent. Since flat light has little to no shadow, the texture of pores or blemishes in the skin can't be seen.
So: soft, diffuse, flat light (filled in shadows) = great looking skin.
Where photographers start running into problems with distracting skin texture on camera is when they use light that isn't for the sole purpose of making skin look great; light is also used to flatter someone's bone structure, create mood, depth or interest in an image. Flat light kills face shape and so most of the time, the light that makes someone's bone structure look ah-mazing (those cheekbones, that jawline!) will also make skin texture and blemishes more evident.
That's where "skin smoothing" comes in.
There are 3 main methods I'm going to demonstrate the results of: Filters, Frequency Separation, and Dodge and Burn.
Each of these popular methods attacks the problem in a slightly different way. Filters blur the skin to remove texture and then add some false, more even texture in it's place, often with some kind of noise or grain. Frequency separation splits the skin information into two layers, a color layer and a texture layer, so that the retoucher can deal with color issues and texture issues each on their own layer without compromising the other information. Dodge and burn is aimed at finessing the light itself by evening out the transitions between the highlights, midtones and shadows that show texture; much like shading does when drawing.
Which method each photographer choses to edit skin has several factors but I'm only going to give the major 3:
1. Personal style
2. How much time there is to work on each shot
3. The purpose/use of the final image
Filters are a valid choice for people who have a heavy workload or need to move quickly through post production and aren't concerned with maintaining accurate or natural skin texture. Time intensive edits aren't always possible for wedding photographers or high-volume shooters who need a quick turn around and decent results, especially if they're getting it mostly right in camera. Clicking an action and masking in a skin effect can take less than a matter of minutes, while de-emphasizing or even completely removing blemishes. Filters can be bought from sites that create Photoshop actions, like Florabella, or in programs that stand alone, like Portriature. The con to this method is that it always destroys skin texture and the three dimensionality of the light, and so can damage the appearance of the subject's bone structure if not used carefully and selectively; so it isn't the kind of technique that can be used for images that need to look natural. You'll never see it used in high-end commercial beauty or editorial work.
Frequency Separation was all the rage for a while, and is now popular among portraitists, too. It's a powerful tool that can make big changes quickly, and is an option for people who have a bit more time to spend per image than high-volume shooters might, or who are working with serious problem skin but don't have a lot of time to edit it. It can make more dramatic, specialized changes than a press-button filter can make, but also requires more time. The problem with Frequency Separation is that is can be over-used very easily and quickly and, as a result, damages skin texture and bone structure, which can make skin look like plastic as well as changing the appearance of someone's face and damaging light quality. Used heavily, it makes the skin texture appear to float above the skin color, and leaves a kind of glow. If it is used selectively and carefully, it can be a serious help to people who need big changes or want a very specific look in a minimal amount of time. This technique can be very handy for glamour or boudoir photographers with a bit of time on their hands to retouch each image, but isn't something you'll see in the high-end commercial or editorial market.
The hard truth is that the most natural looking skin edits also take the most time. This consists of methods the high-end pros have been using for ages: healing/cloning and dodge and burn. It has the most natural results, but also requires the biggest time investment. Dodging and burning a photo to beauty standards, say for a cosmetics campaign, can take hours while dodge and burn for a portrait will only take as long as practice and the area you're working on allow. Dodge and Burn really shines amongst skin editing techniques because it focuses on the root of our ability to see skin texture in the first place: light. It works by evening out the transitions between highlight and shadow, and also has the added benefit of being able to add volume and depth to the image, as well as to emphasize or deemphasize certain areas in the photograph because it focuses on the single element that makes a photograph possible in the first place; light.
There's really no technically right or wrong answer since what technique is chosen depends on the genre, the final use of the image, print size, visual style of the photographer, and so on; but the ultimate, most important thing to know about great looking skin is: it all begins with THE RIGHT LIGHT.
In the gallery below, you'll see examples of each editing technique, followed by close ups for skin texture comparison. I used a beauty image because the results will be the most apparent up close. Be sure to hover over each image and see what technique was used to achieve each effect. Please note: only the actions native to each technique were used to edit, which means that I followed only the steps usual to completing each, so; healing/cloning is a normal part of the dodge and burn retouch process so it was included, yet retouching texture issues when using a filter or action must be done SEPARATE from the action, so isn't included in the example.
***for the best results, click on the image to see the changes in the lightbox***
For my own personal taste, as well as industry standards, Dodge and Burn will always be the way to go. It has the most natural results, the widest application, and keeps the integrity of the skin texture and bone structure of the subject, as well as the light quality.
If you're trying to decide what skin editing technique to use ask yourself: how much time to I have each image? Does the result of this technique fit with my visual style? Does this technique fit within the standards of my chosen genre?
Whichever technique you choose, my advice would be to start off with great light, and then practice, practice, practice, and use a light hand. No one wants to look like a mannequin.
Unless you do...in which case, have at it!