Adding background blur in PS?

marlinspike

Is there some quit and dirty way of adding some blur to everything in a photo that isn't the subject? (PS CS2)

LiquidAir

Depends on what you mean by quick and dirty. Here is the strategy I use:

1. Duplicate the background on to a second layer.
2. Create a mask for your subject on that layer.
3. On the background, clone out the edges of your subject. You need to clone out enough that when you blur the background your subject won't bleed into the background.
4. Now blur the background layer.

This process can be easy or difficult depending on the shot.

wxwax

It's very difficult to make it look natural. Blur doesn't abruptly start and stop. it goes through a transition, from near to far. Trying to replicate that well enough to fool the eye is a real challenge.

As you might be able to tell, I've tried and failed.

marlinspike

I actually want a quick transition.

LiquidAir

wxwax wrote:

It's very difficult to make it look natural. Blur doesn't abruptly start and stop. it goes through a transition, from near to far. Trying to replicate that well enough to fool the eye is a real challenge.

As you might be able to tell, I've tried and failed.

I usually use this technique when my model is too close to the muslin which is a fairly common problem in my tiny studio. For environmentals where the backround has depth I don't even think about trying to simulate lens blur.

colourbox

Photoshop has a Lens Blur filter that's specifically designed to simulate lens blur, down to using a mask to simulate depth of field and options for aperture blade shape, but I've never tried it.

marlinspike

LiquidAir wrote:

Depends on what you mean by quick and dirty. Here is the strategy I use:


2. Create a mask for your subject on that layer.
3. On the background, clone out the edges of your subject. You need to clone out enough that when you blur the background your subject won't bleed into the background.

Ok, I apologize for an idiot, but I don't know what those two steps mean. How do I create a mask for my subject, and I know the clone too but what do you mean by clone out the edges?

EDIT: I figured out how to make the mask, but I still don't know what you mean by clone out the edges.

Thanks,
Richard

jfriend

A background blur tutorial

marlinspike wrote:

Is there some quit and dirty way of adding some blur to everything in a photo that isn't the subject? (PS CS2)

I don't know of any ways to blur the background that don't involve a fairly careful selection or mask of the foreground object. If the foreground object is nice and distinct, that can be quick. If it isn't easy to mask/select, then it will take awhile.

Here's a brief tutorial on 3 different ways to blur the background I did more than 2 years ago. At the time I was using Elements and was more of rookie on post processing, but anything you can do in Elements, you can do in CS2 so it should give you the general idea.

The way I do it today is a modified version of method #3.

• Make a copy of your image in a new layer.
• Select the foreground object with whatever selection tools you want to use on the top layer.
• Save the selection.
• Do a slight feathering of the selection to make the edge not quite so sharp (perhaps only 0.5 pixels).
• Cut out the foreground from the top layer so that layer is transparent.
• Lock the transparent pixels so they won't be impacted by the next step.
• Blur the background on the top layer.
• If the background should not be uniformly blurred, then use a mask on the top layer to block some of the blur. If you want the blur on the ground to fade from nothing at your subject to full blur in the background, you may wan to use a gradient mask to achieve this.
• You could be done at this point. Sometimes, you need to tweak the edge of your blur layer. If you accidentally got some of your subject in the blur, you can try to just erase or mask it on the middle layer to let the subject from below show through. If that doesn't work because the subject is caught up in the visible blur and that's too obvious, then you can't easily fix it. You'll have to restore the top layer, load your saved selection, tweak the selection to not include pieces of your subject and go again from there. If you missed some of the background and it's not blurred, then you'll have to go back to an unblurred layer, tweak your selection and go from there.

In my experience, this is not a simple operation and it is hard to make it look natural. It's way, way easier to shoot at f/2.8 and let physics take care of the blur for you. I shoot all outdoor sports at f/2.8 or f/4 for this reason.

davev

Depending on the photo, (seeing it would help) you could try smart blur.
Filters>blur>smart blur.
I've used it on some photos and have had good results.
Obviously I have reprocessed this shot, but for the most part, the only real change is the smart blur. No masking was done.

without smart blur


with blur

rutt

I struggled with this a few years ago, and the result was a great old thread. I've learned a lot since then, but I've never improved on my understanding of this particular topic, especially once I learned this.

pathfinder

John,

I wonder if any of us thought to look at Andy's sticky at the top of this forum under Extract Tool?

The red bud thread you linked to is right there!!

Kudos to you and Andy!

rutt

Actually I sort of lied. I have sort of learned more than I knew a few years ago about this topic. See: this and this.

I don't want to mislead anyone. You can't do this in Photoshop, you need Mathworks or similar. To quote Dr. It, PhD:

Dr. It wrote:

That is really cool, but how the heck do us normal humans use that theory in
photoshop?

Man, this math is hard!

Nik, the Russian math professor, also took a look and wasn't exactly volunteering to write the Photoshop plugin.

Me, I'm glad to have the reference. Maybe we can outsource the work to India or fund a startup of MIT grad students.