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Old Jul 3, 2004, 2:30 PM   #1
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I really like the Lens Blur filter in PS CS. It does a much better job of blurring backgrounds than a simple Gaussian Blur.

I've added two images to this post. The first is a simple JPG directly from the RAW file. It is an image of a white iris from Leu Botanical Garden in Orlando, FL. I used a Canon 10D camera, a Kirk Dual Macro Flash Bracket, 2 Canon 550EX flashes, and a Canon 180mm "L" macro lens.

As you can see, I pretty well nailed the exposure. I used f/32 for maximum DOF because I wanted to get the iris sharp from petal tip to petal tip. Unfortunately, f/32 also allows a lot of background detail.

I cropped the image to 4:5 aspect ratio. Duplicated the background layer. Converted the image to 8-bits, since the Lens Blur filter is 8-bits only.

For the reduced DOF, I started with a mask of the white flower. I used the red channel to make the mask. It took all of two minutes to generate the mask, save it as an alpha channel, and clean it up with the brush tool. Then I inverted the mask and applied a 1 pixel Gaussian Blur to soften the edges of the mask.

The settings for the Lens Blur filter were:
(1) use the alpha channel as the depth map source
(2) 240 as the Blur Focal Distance
(3) "Invert" check box checked
(4) Hexagon iris shape with 75 for radius and 0 for curvature and rotation
(5) Brightness 20 and threshold 255 for specular highlights
(6) Noise 5, Gaussian distribution
(7) "Monochromatic" checkbox not checked.

The second image shows the final result. You can also see it temporarily on my home page (http://www.thelightsrightstudio.com). I added my new gallery print edge effect to the image. I'm in the process of renovating my galleries, and one of the changes is to use this new gallery print look to my Web images.

The background is much less distracting. I get the benefit of maiximizing DOF for the white iris while narrowing the DOF behind the iris in a way that looks very similar to the bokah I expect with my 180mm "L" macro lens.

Comments are welcome!

Cheers,

Mitch





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Old Jul 3, 2004, 7:19 PM   #2
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Hi,

very interesting experience!

It would be good tosee both pictures with Lens Blur and Gaussian Blur to compare. Where it can be watched?

Now I'm going to your homepage to learn...

Thanx!
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Old Jul 5, 2004, 8:22 AM   #3
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To get a similar blur, you need 20 pixels of Gaussian Blur. That requires that you contract the selection quite a bit and then feather it or blur it. I made several iterations, trying to avoid an obvious halo from the blurring.

With the Lens Blur filter, you get none of that. As I said, I simply applied a 1 pixel blur to the alpha channel of the background around the flower. Then I used that mask, which was pure B&W pixels, as the depth map for the source. That applied the same blur throughout the background.

On other images, when I wanted the blur to grow as objects were in front or behind the subject, I used a gradient as my depth map. White is considered in front of subject. Black is considered behind the subject.

It's a great filter!

Cheers,

Mitch
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Old Jul 6, 2004, 6:46 AM   #4
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Thanx a lot!
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Old Aug 1, 2004, 9:17 PM   #5
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I added a tutorial to my site today that describes how to use the Lens Blur filter to reduce DOF in your images.

http://www.thelightsright.com/Digita...pthOfField.pdf

Cheers,

Mitch
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