What's the proper way to replace a background in a portrait photo

[wienerdog]

I know this is a pretty common technique in Photoshop, but wanted to know if people have recommendations on what is considered the BEST technique to replace a background of a portrait photo with another background?

For instance, how much feathering should I do to my selection of the subject? Should I color-correct with RGB levels on the subject once it's been cut from the background, or adjust the levels BEFORE my selection?

I'm doing some digital shots of people in my office and I would like to replace the bland wall background with a studio-style 'cloud' background.

I did a search on Google but couldn't quite find what I was looking for.

[Drorain]

you'll need to do a selection and mask out the background, you'll have to be pretty thurough though, zooming in as needed, then paint back in to the mask to get the edges you missed. For this you can use a feather brush, try not to make to much of a feather though. Then I would color corrct the layer after you have the background behind it, because as you know from basic color theory, the surrounding colors will influence the look of the person

[PrintDriver]

How many people? Mighta been cheaper to rent, borrow, buy a backdrop...
Water over the bridge...

[wienerdog]

So I guess I can create a new background, which I can probably create with the cloud filter and some blur tool. Then paste the original photo into a layer on top of the new background layer, and then mask out the old background and brush it out. Then do I merge the layers and do color correction? Do I have that right?

[cjoe]

Then do I merge the layers and do color correction? Do I have that right?

Just create a new adjustment layer.

[Ned]

For instance, how much feathering should I do to my selection of the subject?


That depends largely on your image resolution. A 1 pixel feather can be huge or not at all noticeable depending on the resolution of the image.

I generally prefer to make a hard-edged mask, save as an alpha channel, then feather my selection later (either using selection=>feather selection or applying a gaussian blur in quick mask mode.) Also in Quick Mask mode you can easily apply semi-transparent areas by using a grey colored brush. (ie, for clipping water being poured out of a jug, fountain, etc., use a soft brush at maybe 70%-80% black).


Should I color-correct with RGB levels on the subject once it's been cut from the background, or adjust the levels BEFORE my selection?


This all depends entirely on your image. If there's a huge contrast between the selected area and the background, then chances are you should do this before making the selection, as there'll be too much color clipping in just the selected area. If there's not much difference in color range between the background and selection, then you should probably apply the level adjustments on the selection only, to maintain more precise control. It's usually best to adjust each color channel individually, though somtimes using the master channel will maintain the integrity of the picture better.

[urstwile]

I agree with the other contributor here who said it's best to usually start with a hard edged mask and then "airbrush" in the feathering. It's an "al dente" thing. You probably won't need too much around clothing lines, except for shadows, it's more the hair areas that are the trickiest, and the hardest to achieve naturally.

A lot of what you do will depend on (1) what your subject looks like lighting and coloring-wise: are they wearing dark clothes, do they have dark hair, are they wearing light clothes, do they have light hair, etc. and (2) are they going to be on a darker background or a lighter background. For this reason, I'd leave the image in RGB, as it might be you could use some of the lighting effects that are only available in RGB (at least in the version of Photoshop I work in currently, which may be different now).

What I do when I first try to isolate an image from a background, is I adjust my transparency settings to eliminate the checkerboard, and set both foreground and background transparency settings to be a solid that more or less matches the overall background color I'm going for. Granted, you're not going for a solid background color, but this gets you started.

Then start building your selection masks. This is all about the mask, and as was said by a different poster, the paintbrush and airbrush in the mask will be your friends as to the reality of your silhouette against the background. You'll want to constantly increase and or decrease the size of your brush (I've found the shortcut "left bracket" on the keyboard for smaller, "right bracket" on the keyboard for larger to be invaluable with this), and its opacity as you work with the mask, painting and/or airbrushing, particularly in the hair areas. All of these will contribute to your selection.

This is why setting the transparency to a solid close to your final background helps (in my opinion), because you can see a dynamic preview of the effect you're creating. As you edit the mask while looking at the masked image, you'll see right away what's happening.

If possible, always paint at a 100% view, not zoomed out, as the effect of your selection and the feathering can be distorted when zoomed out.

Good luck! It's not the easiest trick to pull off naturally, but it is achievable. Use channels to help you figure out selection edges. They're masks of a sort too, although not selection masks per se, but they can help you make judgment calls. Use gradient masks on adjustment layers where necessary to match the lighting of the new background.

Duplicate layers, it might be certain areas might be easiest to work on separately. Sometimes the dodge and burn tools can also be your friends in this type of work as well. Hopefully you don't have too many images to do, this is an image by image type of project.

Make sure to add some noise and then blur your new background (unless you're scanning something in with a texture)! Makes it look a bit more realistic, like film grain. Otherwise, it'll look all "filtery".

Sorry to be so wordy in this response. :o

[Jason Fraker]

be sure to post the results in the Showcase, so Pixel8 won't get all in a tissy.

[wienerdog]

Thanks for the help folks! I took a series of photos of staff for the company with my 4 megapixel digital camera. I have a good Photoshop technique book I let a friend borrow that I'm hoping to get back this week. I'll consult that as well.

Is there something that's recommended to do to digital photos? I've seen people mention to add a slight gaussian blur to all digital shots, for some reason. Wasn't sure why or where I saw that.

[cjoe]

When (if) you make an alpha channel out of your selection and you have your basic mask down i.e. pure black area and pure white area. Apply the appropriate Gaussian Blur to your alpha channel, then use Levels sliders to fine tune your blur.