The basis for soft-masking is a professional image editing software such as Photoshop, which offers the possibility to clip tricky elements like hair, fur or smoke with the aid of an alpha channel and masks.
The Process of Soft-Masking
A professional editor always uses masks to preserve the original image during the editing process. Once the mask is deleted, the original image is restored. Often alpha channels are used for soft-masking as they can store additional information about the transparency or saturation of an image.
After creating the alpha channel, the area that shall be preserved is coloured in white. The are that shall be removed, is coloured in black. In order to capture all details, it is helpful to enlarge a section of the picture at the transition zone between the element that shall be preseved and the background that shall be removed. Now, within this enlarged section, the editor uses an appropriate brush to paint the object in white –right up to the sensitive area, e.g. hair. On the opposite site one does the same with black. So as to complete the clipping of the hair, the level adjustment (tonal correction) is used. The result can be examined by moving the black and white areas. In case, the result isn't satisfying yet, final corrections have to be made by adjusting the hardness and diameter of the brush. A soon as the editor is happy with the results, he repeats the process with other sections until the whole fringe is edited.
Thereupon, the whole graphic is painted to create a complete mask that can be clipped in the next step. The selected element is now surrounded by a dashed line in the alpha channel. Finally, the layer mask is added to the original image.
Like this, even the trickiest element of an object can be clipped precisely without losses.