I've done a lot of this work in the past and tried enough different methods to be sure that there is no quick way to do it that gives good results. You can have either quick or good, but not both together. I'd love to be proven wrong on this as I imagine I'll have to do a lot more of this work in future.
Manually cut out the subject (with the pen tool, lasso etc.), fill the outside area with white. This is the most time consuming but provides the best results. Works best with head/torso shots as if you're working on a full length shot this method removes shadows which prevent the subject being grounded (they look like they're floating in the air). Hair is very problematic so I often rely on the below method for the hair.
Blowing out the background, i.e increasing brightness contrast until the background goes pure white. This can be done globally if you're lucky, but most of the time the background brightness will shift across your image (due to shadows / light falloff), so the amount of brightening to blow it out will vary. I work around the subject with a selection along the edge of the subject, fading out gently into the subject, and adjust the curves until the background goes white locally, then move the selection on to the next part of the edge. Downsides of this method are that it is still time consuming, can produce artifacts / colour shifts in the edges of the subject, and it only works if the background is fairly bright / even to begin with. Also it can't handle shadows.
Blurring the background. Blurring evens out creases well, and copes with shadows and changes in background brightness. The problem with this method is you can't get too close to your subject(s) without blurring them, so you can blur the large areas but then you often need to do some manual fixing around the edges of the subjects using the above methods.
I know your question specifies "in photoshop", but it really does bear repeating that if you can get this right in-camera you can save a load of work in post. (Obviously, you know this!) I have found this out the hard way :(
I realise that this might not answer your question, nor solve your immediate problem, but it does help to make the site more complete for people researching the problem of getting the background right.
For dirt and smudges, if your background is untextured you can use Filter > Noise > Dust and Scratches. This will remove any defects, of any size you choose, in one go. I would make a rough selection of the background, put into a new layer, run the dust and scratches filter. Then you have the ability to use a mask if you want to be more selective about where you apply, and don't apply, the effect. If you make the layer a smart object you can revise the filter settings if you have over- or under-done the filtering.
For larger patches, use the healing tools (particularly the patch tool). Select an area with a defect, then drag that to a good area. Photoshop will fill the defective area with something that has nice texture and color.
An alternative is to select an area that is good (no defects) and duplicate that into a new layer. Move that over the area that has problems. Cover the new layer with a black mask, then paint in with white, at low opacity, where you want to cover up the defects. This means you end up with all texture and light variations, rather than painting a solid color that will look artificial. You'll need to use an area that closely matches the color and brightness (or apply a levels/curves adjustment to make it match)
Another simple method is to select an area, then Edit > Fill and select Content-Aware. This will remove the defect and attempt to match color, brightness and texture from surrounding areas. This works well in the interior, but may have problems near edges.
If you have wrinkles or folds that are not close to the subject, you can use content-aware scaling to stretch the background (leaving the subject unaltered) so that the areas containing the defects are dragged out of frame.
If you are shooting from the same perspective a lot, so that the defects are in the same position, you can create a mask in photoshop to cover them up, then for future shots, you can create a new layer and reuse this mask, adjusting the new masked layer each time without having to find the defects and figure out a way to cover them over and over again.
As mentioned above. The best thing is to use a clean backdrop. Sometimes I don't have control over the backdrop at all. I use a mix of content-aware, patch tool and spot healing brush tool to clear any marks on the backdrops.
Transform your studio setups with just a few clicks using the power of AI in Photoshop! This step-by-step tutorial will teach you how to seamlessly remove imperfections, wrinkles, and distracting objects from your photos, resulting in flawless and captivating images.
If you want to extend a background, you can use the Generative Expand tool. Generative Expand is another new feature in Photoshop that uses AI to expand images. To use Generative Expand, you will simply need to click on the sides of your image and drag them out.
In this Photoshop Effects tutorial, we'll learn how to quickly and easily create a simple photo studio background in Photoshop which can then be used to make any portrait-style photo look as if it was taken in an actual photo studio, even if it was really taken in your office, your kitchen, your neighbor's backyard, or basically any place other than a photo studio. As with most Photoshop effects, this background works best when used with the right type of photo, so since we're trying to make it appear as if the photo was taken in a portrait studio, it helps if the person in the photo is dressed nicely, hair in place, and sitting in one of those completely unnatural portrait studio poses.
One other thing to keep in mind before we begin... If you're planning on taking a photo to use with this background, try to have the person (or people) sit in front of a plain white background if possible when you take the shot, since that will make it much easier to select them in the original photo when you go to move them in front of this new background we're about to create.
To begin, we need to create a new Photoshop document, so go up to the File menu at the top of the screen and choose New, or use the keyboard shortcut Ctrl+N (Win) / Command+N (Mac). Either way brings up Photoshop's New Document dialog box. Let's use a standard size of 8x10 inches for our new document, so I'll select that from the list of Preset sizes. I also want to make sure that I enter 72 pixels/inch for my Resolution value:
Now, if you know anything about image resolution and print quality, you're probably wondering why I've set my resolution to only 72 pixels/inch, which is far lower than the professional print quality resolution of 300 pixels/inch, and you're most likely thinking that if we go to print this image at only 72 pixels/inch, it's going to look rather horrible, and you'd be right. There's no way we can print our image at such a low resolution and expect it to look good. Don't worry though, we won't be leaving it like this.
The reason we're starting off at only 72 pixels/inch is because we're going to be using Photoshop's Clouds filter to help us create our background, and the Clouds filter is resolution-dependent and only works well at low resolutions. If we tried to use the Clouds filter at 300 pixels/inch, we'd get a whole bunch of really small clouds instead of a few large ones, and we want the larger ones for this effect. I'll show you what I mean in just a moment. For now though, go ahead and create your new document by clicking OK in the top right corner of the dialog box.
We need our background to be black, so press the letter D on your keyboard to reset your Foreground and Background colors if needed, which sets black as your Foreground color (white becomes your Background color), and then use the keyboard shortcut Alt+Backspace (Win) / Option+Delete (Mac) to fill the document with black:
If we look in our Layers palette, we can see that we currently have only one layer, the Background layer. We need to add a new blank layer to the document, so click on the New Layer icon at the bottom of the Layers palette (it's the icon directly to the left of the trash bin):
With the new layer selected in the Layers palette (the currently selected layer is highlighted in blue), go up to the Filter menu at the top of the screen, choose Render, and then choose Clouds. I don't think you'll find too many people who'll claim that Photoshop's Clouds filter gives you anything remotely close to realistic-looking clouds, but still, your document should now look something like this:
The Clouds filter gives you something different each time you apply it, so if you want to experiment with it a little to see different variations of the effect, simply press Ctrl+F (Win) / Command+F several times to re-apply the filter and you'll see a different cloud pattern each time.
Before we continue, just to show you what I meant earlier about how the Clouds filter would give us a different result if we tried running in at 300 pixels/inch instead of 72 pixels/inch, here's what we'd get with it at 300 pixels/inch:
We've added our clouds but they're too intense at the moment. We need them to be much more subtle, so go to the Opacity option in the top right corner of the Layers palette and lower the layer's opacity down to 40%:
We need to merge our two layers together at this point, and we can do that with the keyboard shortcut Ctrl+E (Win) / Command+E (Mac). If we look again in our Layers palette, we can see that two layers have been merged into one:
Let's make the background look a bit more interesting by adding a little texture to it. Going up to the Filter menu once again, this time choose Brush Strokes, and then choose Spatter. When the dialog box appears, enter 10 for the Spray Radius and 5 for the Smoothness, then click OK to apply the filter to the image:
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