About selecting pixels
A selection isolates one or more parts of your image. By selecting specific areas, you can edit and apply effects and filters to portions of your image while leaving the unselected areas untouched.
The easiest way to select pixels in your image is to use the quick selection tools. You can also select areas of a certain shape with the marquee tools or use the lasso tools to make a selection by tracing an element in your image. It’s also possible to make selections based on a range of colors in an image. There are commands in the Select menu to select, deselect, or reselect all pixels.
In addition to pixels, vector data can be used to make selections. Use the pen or shape tools to produce precise outlines called paths. Paths can be converted to selections.
Selections can be copied, moved, and pasted, or saved and stored in an alpha channel. Alpha channels store selections as grayscale images called masks. A mask is like the inverse of a selection: it covers the unselected part of the image and protects it from any editing or manipulations you apply. You can convert a stored mask back into a selection by loading the alpha channel into an image.
Note: While paths can be converted to selections, selections can also be converted to paths.
About layer clipping masks
A clipping mask is a group of layers to which a mask is applied. The bottom most layer, or base layer, defines the visible boundaries of the entire group. For example, suppose you have a shape in the base layer, a photograph in the layer above it, and text in the topmost layer. If the photograph and text appear only through the shape outline in the base layer, they also take on the opacity of the base layer.
You can group only successive layers. The name of the base layer in the group is underlined, and the thumbnails for the overlying layers are indented. Additionally, the overlying layers display the clipping mask icon.
Note: You can link the layers in a clipping mask so that they move together.
About adjustment and fill layers
An adjustment layer applies color and tonal adjustments to your image without permanently changing pixel values. For example, rather than making a Levels or Curves adjustment directly to your image, you can create a Levels or Curves adjustment layer. The color and tonal adjustments are stored in the adjustment layer and apply to all the layers below it; you can correct multiple layers by making a single adjustment, rather than adjusting each layer separately. You can discard your changes and restore the original image at any time.
Fill layers let you fill a layer with a solid color, a gradient, or a pattern. Unlike adjustment layers, fill layers do not affect the layers underneath them.
Adjustment layers provide the following advantages:
Nondestructive edits. You can try different settings and re‑edit the adjustment layer at any time. You can also reduce the effect of the adjustment by lowering the opacity of the layer.
- Selective editing. Paint on the adjustment layer’s image mask to apply an adjustment to part of an image. Later you can control which parts of the image are adjusted by re-editing the layer mask. You can vary the adjustment by painting on the mask with different tones of gray.
- Ability to apply adjustments to multiple images. Copy and paste adjustment layers between images to apply the same color and tonal adjustments.
Adjustment layers have many of the same characteristics as other layers. You can adjust their opacity and blending mode, and you can group them to apply the adjustment to specific layers. Likewise, you can turn their visibility on and off to apply or preview the effect.
Because adjustment layers contain adjustment data rather than pixels, they increase file size far less than standard pixel layers. If you are working with an unusually large file, however, you may want to reduce file size by merging adjustment layers into pixel layers.