Photoshop Effects: Creative Focus with Lens Blur
Photoshop Effects and Photo Effects at Photoshop Essentials.com
Step 3: Select The Brush Tool
As I mentioned, we're going to be painting on our new alpha channel with white to create our Depth Map, and to do that, we need the Brush Tool, so select it from the Tools palette:
Step 4: Lower The Opacity Of The Brush To 50%
With the Brush Tool selected, go up to the Options Bar at the top of the screen and lower the brush's Opacity to 50%:
When creating our Depth Map, any areas we leave as pure black in the alpha channel will have the blurring effect applied to them at full strength. Any areas we paint with pure white will not have any blurring applied to them at all, and any areas we paint with some shade of gray will have blurring applied to them at various strengths depending on how close that shade of gray is to black (full strength blurring) or white (no blurring). By setting our brush to 50% opacity, this allows us to slowly build up areas of blurring and non-blurring as we paint on the alpha channel, instead of just saying "I want 100% blurring here and 0% blurring here" with nothing in between.
Step 5: Turn The RGB Channel On
Currently, our image is filled with black, which makes it a little difficult to see what we're painting over in the image, so let's fix that. While still in the Channels palette and with "Alpha 1" still active (you know it's active because it's highlighted in blue), click inside the empty box to the left of the "RGB" Channel at the top. When you do, you'll see the eyeball icon appear inside the box (it will also appear in the empty boxes of the Red, Green and Blue channels since, as I mentioned earlier, the RGB channel is just the composite of the other three channels), which tells us that the channel is now visible:
With the RGB channel visible, if we look back at our image, we see that it is no longer filled with solid black. Instead, it's overlayed with red which allows us to see our image underneath:
Don't worry, our image is not actually covered in red. We're still looking at the alpha channel, not the image itself. The red just makes it easier for us to see what we're doing. The areas overlayed with red at full strength (which at the moment is the entire image) represent areas filled with pure black on the alpha channel. As we paint with white on the alpha channel with our brush, which we'll do in a moment, we won't see white appearing in the image. Instead, the red will begin to disappear in the areas we paint over, as if we're erasing the red with our brush, revealing more of the original image in those areas. The less red there is covering an area, the less blurring will be applied there when we go to use the Lens Blur filter.
If we were to paint with white with our brush set to 100% opacity, we would be completely removing the red from any area we paint over, which would mean that no blurring at all would be applied to those areas, while 100% blurring would be applied everywhere else, giving us an "all or nothing" situation. But since we've lowered the opacity of our brush to 50%, the more times we paint over the same area, the more white we'll be adding to that area on the alpha channel and the more the red will disappear in that area in the image. This gradual build-up of white on the alpha channel (and gradual lessening of the blurring effect applied to the image) is what gives us so much control with the Lens Blur filter, much more than we could ever get using the Gaussian Blur filter, at least not without using a layer mask (although technically, the Lens Blur filter's Depth Map and a normal layer mask are really the same thing, but we'll save that for another tutorial).
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