Howard,
Normally speaking ‘portrait backgrounds’ tend to be on a flat vertical plane and therefore at fixed distance from the camera viewpoint.
When this is the case, why would you want variable blurring, which is intended to reproduce the depth-of-field effects of a camera lens when used at large aperture settings?
I don’t think that Martin Evening has explained very well what he is trying to achieve in that tutorial (aside from the fact that you need to get the pdf to see the full tutorial). Forgetting about the main blurred background, the depth map is being applied to the table to give the impression of the foreground being out of focus as well as the background- the sort of effect you might get with a large aperture and very careful focusing. The reflective gradient is used as this gives a mirror-type gradient. The lightest parts of the mask become more out of focus than the darker parts when the filter is applied so the front and back of the table are more out of focus than the middle where the plant is.
As Len says, I can’t see any advantage in applying a depth map to a flat portrait background.
Len and Mick —
I guess I did not explain my situation well; sorry.
I do not wish to apply the Lens Blur on a TRUE studio portrait image, having an artificial backdrop. Instead, the images I’m working on are non-professional snapshots of individuals, where the individual is the main subject — let’s call this the "foreground" — while the background is some unimportant scene, such as a city street, someone’s backyard, etc. While these backgrounds are unimportant, they do, however, have depth/three-dimensionality. Consequently, I believe the Lens Blur filter might provide a better/more realistic way to draw the viewer’s eye away from the background, and to the foreground subject.
You probably understand me now, but I’ll provide one example: I restored a snapshot from the 1950’s of a young lady standing in her backyard. She’s standing on grass; in the background is more grass, some bushes, then a tree, and way in the back are houses. I could simply blur the background, i.e., everything but the young lady. However, I’d like to try the Lens Blur filter, whereby I believe I should be able to achieve an effect that would, for example, leave the grass immediately at the young lady’s feet mostly in focus, but as the eye moves behind the foreground of the young lady, the grass becomes more blurred, the bushes more so, the tree even more so, and the houses in the rear quite blurred.
So you see, I believe my objective is in concert with the intent of the Lens Blur filter. But, as stated in my original post, I have not been able to create an effective Depth Channel/mask.
Help appreciated.
Howard
OK. The basic idea is pretty straightforward. You need to select the background area that you want to apply the filter to and then save that as an alpha channel (go to Channels palette with selection active and hit the second button from left at the bottom).
Then click on that channel so you are looking at a black and white mask in the image area. Then apply a foreground to background gradient to the channel with white and black as foreground and background colours (or vice versa) with the selection marquee still active. This will leave you with a gradation in the channel from white through to black.
When you apply the filter, the white areas will get the strongest effect and the black areas will be unaffected. The grey areas will get an intermediate effect. You will need to experiment with applying the gradient to get your desired effect, perhaps by editing the gradient stops. You could also simply paint on the channel but the gradient will give a smoother effect.
Mick —
Thanks for the help, but I’m still confused with respect to the SECOND of your three paragraphs above.
I, of course, made a careful selection of the foreground image (three girls). I then executed "Select>Inverse", thereby saving the selection of the background. This creates and saves an alpha channel of the same. Then in the Channels palette, because it is a B&W image there are two Channels: "Gray" and "Background". I highlight the "Background" channel.
It is at this point that my experience differs from your instruction. Specifically, the foreground (the three girls) is BLACK and the rest of the image, i.e., the background, is WHITE.
Beyond that, no matter how I "play" with the Gradient tool (black to white, white to black, edge to edge, middle to edge, edge to middle, etc.), I cannot achieve what should (I hope) appear to be an untouched foreground (not to be blurred) and a Gradient radiating out from the foreground to the background.
So, should I give up entirely and simply take up golf, or is there any hope of figuring out how to create a Depth Channel of the type I need?
Thanks for your help.
Howard
I’m not sure what is going wrong. Once you have created the channel you need to use the gradient tool on the channel mask by selecting the alpha channel. Leave the selection active so that you don’t affect the black foreground and then use the gradient tool to change the white area from dark in the near background to light in the far background. This will blur the far background more than the near background.
Then, select the Gray channel (or the layer in the layers palette) and apply the blur to this (perhaps this is where it’s going wrong – you are applying the blur to the mask). If you want to experiment using Gaussian Blur, load the alpha channel as a selection and then apply the blur to the image (not the mask).
When you use the Gradient tool, make sure to set your blend mode to "Multiply" in the option bar on the top of the screen.
I think that is what you are trying to achieve. If not, ask away.
OK Mick and Jonathan, I finally got it to work.
Here’s where I failed in my former attempts to create the "Depth Channel".
1. Foreground/Background being Black/White — Since I "selected" the Background and saved it, my Background alpha channel was "correct" irrespective of whether it was black or white.
2. I correctly highlighted my Background alpha channel and tried all the Gradient Tool formats, but the standard black to white gradient was the proper one to use. I was in "Multiply" mode.
3. The problem was that I IMPROPERLY left the Background alpha channel highlighted when I entered the Lens Blur dialog. Consequently, in the Lens Blur dialog, I did not see the true background of my image, but instead the gradient covering the background! When still in the Channels palette, I should have highlighted the "Gray" channel (this is a B&W image). After doing so, upon entering the Lens Blur dialog my full image was visible.
4. Then in the Lens Blur dialog, from the drop-down window I selected the "Background" alpha channel and applied varying amounts of Radius until the background blur was ok. Note, when earlier applying the gradient, because my foreground subjects (three people standing together) are standing on grass and the background slowly progresses from more grass to bushes to trees to houses in the background, I applied the gradient from the bottom to the top of the image. After applying the blur filter, the grass within a few feet of the subjects’ legs and feet show no blur at all. As the eye moves further back, the blur is progressively greater — which is exactly what I was trying to achieve, rather than a uniform Gaussian Blur.
The only matters yet to figure out are the "Blade Curvature" and "Rotation" functions. At least in the image I’ve been working on, I see no effects of adjusting these sliders.
Mick and Jonathan, again thank you for your help.
Howard
Howard,
To answer your last questions regarding Blade Curvature and Rotation, try the following. On an image with specular highlights (some bright light sources), zoom in, set the iris shape to triangular or square (as that will be more evident) and then adjust the curvature and rotation. Whilst the effect is subtle, it’s also very precise, and on the correct image is pretty impressive. I hope that helps, and I’m glad to hear that you’re all enjoying Lens Blur.
Thanks,
-Bryan
Howard
Glad you got it working. I thought you must have been applying the filter to the mask alright. You can use the same technique for other adjustments and filters such as Unsharp Mask and Gaussian Blur for example.
