The original bread image we have was shot on a plain background, but needs to be clipped so it can be used on any background. At the same time, we want to keep the natural shadow, since adding a drop shadow is less realistic and harder to keep consistent with the lighting of the shot. [Click tutorial images to view them at full size]
1. Clip Starting Image
Here is the original image. Start by creating a regular clipping path around the product. Don't mask it just yet – save the path so it's readily available a little later.
2. Review the RGB Channels
Find the color channel with the strongest shadow. This is typically blue or green. In this case, we'll pick up the blue channel since it will use less severe curve adjustments to wash out the background.
3. Duplicate the Blue Channel and use curves to wash out the background
To avoid confusion, rename the duplicate channel to something like "Shadow Channel". Make sure this channel is the active channel for the next steps: Use curves to wash out the background. The histogram generally gives a good indicator of where the white point needs to be to ensure that the background is white (255).
The idea here is to get pure white around the product and its shadows and not necessarily get a fully white background. Try to avoid really severe curve adjustments in order to keep the shadows more natural. Dark spots/blemishes can be erased if needed.
Edging the curve slightly down ill darken the mid tones to correct for the lighting that occurs when you set the white point:
4. Blur the channel
Use Gaussian Blur to slightly blur the channel. It'll help smooth the shadows, and drop out some unwanted textures. At this point, you can retouch any crumbs or undesirables that might fall in the shadow. It doesn't take much blur, somewhere between 1 and 3 pixels will get proper smoothing.
5. Invert the channel
Invert the image (⌘ + I). If you don't, you will fill the background instead of the shadow in the next couple steps. Crucial. (Though if you miss it, you can always Select > Inverse when the time comes).
6. Create shadow layer and white background layer + mask product
Keeping an untouched copy of your original layer is standard practice in non-destructive editing so you can revert to it if needed. Create an empty shadow layer – this is where you'll paste the shadow from the alpha channel. Also create a white background for visibility. The order should be:
Also in this step, pull up the clipping path you made in the beginning and mask the product to hid the original background.
7. Select contents from shadow channel, fill into shadow layer
Head to the alpha shadow channel you made, and load it to a selection (⌘ + Click the layer icon).
Back in the Layers panel, make sure your empty shadow layer is active, and fill the selection with your shadow color (in this case, 100% black).
(Note: it won't look like the shadow is selected, but don't sweat it – Photoshop just isn't showing the marching ants on such a faint selection).
8. Adjust opacity of the shadow and remove or blur out edges
Reduce the opacity of the shadow as needed. At 100%, the shadow may look unrealistic and too strong against the a pure white background. If you're using a background other than white, set the shadow's blending mode to Multiply.
The Gaussian Blur from earlier has blurred the shadow outside the edges of the product. The mask of the product is also pretty tight. There are a few things you can do about this. For a soft edge, simply blur the shadow around the edges. If you want to remove it completely, erase or mask out the edges of the shadow.
Thanks to Dave Haas for teaching me this process :)