Making a good Feathered Selection in Photoshop
For those of you who use Photoshop CS and above, making a selection in order to do a localized adjustment to an image, can be daunting particularly as it relates to creating smooth, seamless transitional lines that don't reveal your changes in a hard edged way.
One easy way to accomplish this is to simply use whatever tool you wish to use to make your selection around your object, (ie. .the lasso tool, magnetic lasso, rectangular tool, etc. . ) and then after the selection is made simply type 'q' on your keyboard to enter the 'quick mask' mode.
Where you have made your selection is now surrounded by a red tinted mask. Everything red will be hidden or prevented from being modified by any changes you make. But chances are the edges of the mask are still very sharp and hard edged. If you leave them like this they will show off any changes you make as a hard line of demarcation on your image, particularly if you are making exposure, brightness or saturation changes to the selection.
So what you want to do is feather the edge. With the quick mask still active, simply click on 'filters', 'blur', 'gaussian blur' and set the blur amount to a level that makes your mask edges blur appropriately so that you create a nice long transitional edge to your selection. The advantage of this is that instead of trying to 'feather' your selection blind as you would have to do if you simply used a lasso tool and then tried to set a 'feather' amount on the toolbar, you now have a real-time, visual display of exactly how far your feathering will extend beyond your selection.
Once you have the blur amount looking like you want it, click ok, and then exit the quick mask mode by hitting 'q' on your keyboard once again. Now you will be presented with the famous little marching ants that indicate you are back to your selection. Once there you can adjust saturation, sharpness, levels, contrast, exposure, vibrance, or any one of many adjustments available, to your selection area. You will notice that the soft feathered transitions will make your adjustments seamless and invisible.
You can also hide the selection by simply clicking Alt-H, or Option-H on the Mac, so that you can see your changes without the 'marching ants' getting in the way. To see your selection again, simply click Alt or Option-H once again.
Have fun with this method.
Photo credits: Lightart.