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Sunday, December 11, 2011

Give Your Photos a Dreamy Haze Simulating a Diffusion Filter

You've just finished tweaking a great photo of yours: you think it's great but you feel it's missing something. You think that the image conveys a feeling of peace and relax and that it would really benefit from that dreamy haze you've often seen in somebody else's portraits. But you don't know how to do it.

One of the commonly used tools to achieve to give that look and feel to an image is a diffusion filter. Dreamy wedding pictures or studio portraits (such as newborn babies') are probably done that way.
The problem is:
  • You need such a filter.
  • You need a lens which you can put that filter on.
  • You need to carefully plan such a shot in advance.

Fortunately, it's not difficult to simulate such an effect in post production: you only need a photo editing tool with basic filters and layer support (such as Adobe Photoshop, Adobe Photoshop Elements or The Gimp). In this blog post, we're using a technique that's particularly suitable to portrait photography. If you're trying to tweak some landscape image, however, I suggest you take a look to the blog post about the Orton effect and see which technique best suits your image.

Beware: as usual, this isn't an advice not to try and get things right out of the camera.

The Basics

To simulate the diffusion pattern provided by a diffusion filter, we're going to blur the image with a blurring filter. The blurred image itself isn't sufficient, because you're going to lose too much detail. Instead, we'll blend it with your original image to achieve the diffusion effect.

The original image we'll use in this tutorial is the following:

Original Image

I don't think this image needs an additional dreamy look and feel: in fact, this is the final post processed shot and I'm keeping it as is. However, I chose it because it's a good candidate to show you some problems you may encounter on the way.

The first thing we'll do is duplicating the background layer:

Duplicate Layer

The next thing we'll do is blurring the new layer using the Gaussian Blur filter. The rule of thumb we discussed in the blog post about the Orton effect still holds: you need to use a blur radius sufficiently wide to blur the image while preserving overall detail. In this case (the image size is 4208x3264 pixels), I'll use a 30 pixel radius to achieve the following blurred effect:

Blurred Layer - Radius: 30 px

As you can see, the image is blurred but overall detail is not lost: in the eyes, for example, you can clearly see the iris edges and most of the features of the kid's face.

Now we're ready to blend the two layers. Depending on the image, we're probably going to use one of the following blending modes:
  • Screen.
  • Overlay.
  • Multiply.

If you recall the discussions on the previous blog posts, these three blending modes act differently on the image:
  • Screen will produce a brighter image, since it brightens a pixel according to its brightness.
  • Multiply will produce a darker image, since it darkens a pixel according to its darkness.
  • Overlay will both Screen and Multiply the image, according to a pixel brightness, producing a more contrasted image and preserving highlights and shadows.

As a rule of thumb:
  • Assuming the exposure of the image is already correct, we're going to use the Overlay blending mode.
  • If your image is a bit underexposed, it may benefit from using Screen instead.
  • If your image is a bit overexposed, it may benefit from using Multiply instead.

As usual, you've got to try and decide yourself. In this case, since I'm happy with the image exposure, we'll use the Overlay blending mode. The result is:

Final Result - Layers Overlaid
You can clearly perceive the diffusion pattern and the dreamy haze it shed over the image.

Fine Tuning

This is just the beginning. In this case, I find the image is much too dark now. The quickest way to fix it is modifying the overlaid layer opacity. This is the result setting its opacity to 80%:

Overlaid Layer - Opacity: 80%

Beware that setting the opacity too low will also remove the dreamy haze: in this case, I usually won't go below 80% and would try to fix the image exposure by fixing the original layer instead.

Using the same technique, you can control the quantity of "blur" that you're going to add to the image.

Obviously, you could also add an additional layer below the blurred one and fix exposure on it. You could use an adjustment layer, if available, or just use the Screen blending mode to raise the image exposure. The following picture is the result of 3 blended layers (from bottom to top):
  • The original.
  • A copy of the original, using the Screen blending mode and 50% opacity.
  • A copy of the original, gaussian blurred, using the Overlay blending mode.

Three Layers

But The Image Is Over-Saturated

The biggest problem of the images we're producing, however, is not exposure: it's color saturation. This is a common problem when using some blending modes such as Overlay. Raising the contrast of an image, in general, will boost color saturation as a side effect. This may be good in some kinds of photography, such as landscape, but it may be bad in others, such as portrait photography. A more saturated flower may look good but... do you notice the orange hue of the kid's hue in the final images we got so far? That's something you should always try to avoid. Ultimately, this is the reason why I chose this image for this tutorial.

Fortunately, this is again very easy to fix. Assuming once more that we're happy with the initial image color saturation, I usually reduce the saturation in the blurred layer until I'm happy with it. If the photo editing tool that you're using supports adjustment layers, this is really easy: just add a saturation adjustment layer and play with it until you like the result. If your editing tool does not supports it, you're going to use the Saturation tool back and forth until you're happy with it.

However, especially in portrait photography, I usually convert the upper layer to black and white, thus removing all of the color saturation from the overlaid layer. Once more, depending on the tool you're using, you may also be able to achieve better results fine tuning the black and white conversion. Adobe Photoshop, for example, lets you adjust the RGB channels intensity during the conversion:

Abode Photoshop Elements - Black and White Conversion Window

If you're not happy with the result, you can tweak the channel intensities. Depending on the image, I'm usually pushing up or down the red channel intensity until I like the end result.

This is the final image, using a black and white blurred layer:

Final Image - Black and White Blurred Layer Overlaid

It's far more natural, even if still very contrasted.


We've seen how you can use very simple layer manipulations to achieve a variety of effects. So far, we've only used the Screen and Overlay blending modes, and there's a world of possibilities for you to discover.

As a rule of thumb, you've also seen as the Overlay blending mode affects your image contrast and color saturation. Although I recognize that "punchy" images may look appealing at first, I don't really like excessive color saturation in portraits and I always end up with cooler images. That's just a matter of taste, however.

Also, I find that the dreamy haze best suits less contrasted and brighter images.

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