A Image or layer mask is the use of masks so that only certain parts of the image are shown. For example, a shape would be drawn in the base layer this is known as the mask (the layer right at the bottom) after that all layers and images placed above that layers would only show the portions of the image that fall within the area of the Mask and the parts of the images that are outside of the mask would be hidden this is known as a clipping set.
Image Masks can be used to create very powerful visual effects, from techniques such as image blending to stylizing texts. Image Masks can be used to make some bold statements. Image blending refers to the use of two source images which are blended into one. Stylized texts use fonts and textboxes as the mask, so the text is in the base layer and the images are placed over it. All images placed on it afterward take the shape of the text at the base of the image. This can be further improved by adding a different background than that of your clipping set and from the use of alpha channels.
Alpha channel masks allow control of transparency and color over a selected area, as alpha channels are a channel rather than an actual selection on the image, the mask itself can be saved to the image for future use or for use on a different image. Alpha channels are a more accurate masking method then image mask or layer mask, which is used when the background is complex or noisy (i.e. jungle or extreme lighting). As Alpha Channel mask require more time so it’s more expensive than other similar services but provides a better quality.
Another form of masking is the Image Mask which is used for transparent masking and hair or fur masking this is used when intricate work needs to be done to remove or crop an object out of its back ground It is considered a more advanced level of clipping mask, as it works in a similar method but this method is more adapted for images that have many gaps that would be impossible to clip individually.
Clipping Mask vs. Layer Mask
Layer Mask is a one to one masking service, which means a single mask is applied to a single layer. Although masks can be replicated on other layers it will ultimately mean that each layer has its own mask, whereas a Image mask has a one to many masking style, which means that a single mask can be applied to many layers.
So in a layer mask each layer in the image has a separate mask so although the result may appear to be the same as that of a image mask, a layer mask requires much more time to perform and is also denser in terms of file size. In a image mask as a single mask can be applied to multiples layers, the process is achieved much faster and the file size is smaller than that of a layer mask.