I have been asked by several people how-to do a Photoshop Isolation over white effect, to help stop QA rejections for stray Isolation.
We took an image in a studio with a set of cheap studio lights from EBay, the backdrop was just a king-sized white flat sheet, hanging from the wall and draped over a chair.
This diagram shows the setup, we had the background metered at f11 and the subject f8, this was the best we could do with the lights we had.
First open the Image in Photoshop and check for focus (sharpness) and general composition, in our example we are happy with this image but the background is not clean so we can make a start.
From the Main Menu we choose Layer > New Adjustment Layer > Levels.
We automatically get the Levels dialog box appear, under the Histogram there are three sliders, slide the left (Black) slider to the right, this will expose the areas we need to clean, as you can see the background was not as white as we thought there is a lot of cleaning up to do, even on nice white backgrounds it is worth checking this way.
We now need to select the Dodge Tool with a setting of Highlights and 10%, as we want to remove some large areas first so we choose a large brush (300) this will be used for the first pass.
From the Menu Window > Layers (F7) Select the layer called Background, then using the Dodge tool remove the larger areas of discoloured white, carefully work as close to the image as you can.
Once you have done as much as you can, reduce your brush in steps size (30-10) and then View > Actual Pixels, now you can work the detail, you can even change to 5% or use a finer brush, take as many passes as you need reducing the brush or Exposure, but only practice will prove your best workflow.
As you can see we finished with a size 10 brush, when you are happy with the Image, from the Window > Layers, select the adjustment layer (Layer 1) right mouse click and delete this layer, you are left with the background image, nice and clean, save as new image jpg quality 12 and you are finished.
And here is our image all finished, with a nice white background with no stray areas.