Photoshop

Layers

A photoshop document is composed of layers. In the layers window the layers are listed in order. Layers conceal the layers beneath them, but because of the alpha channel, lower layers can nevertheless contribute to the final image.

hiding: In the layers window the eye icon can be toggled to show or hide a layer. Hiding a layer reveals what is beneath it.

naming: Photoshop assigns names to layers, but this names can be changed by double clicking on the name in the Layer window. When there are lots of layers, it can be challenging to keep track of what each layer contains. Photoshop puts small images in the layer window, but assigning meaningful names is also a big help. Hiding layers with the eye icon is sometimes a quick way to figure out what is in a layer.

opacity: Each pixel has an alpha channel, but also the opacity of the entire layer can be adjusted. Select the layer in Layer window. At the top of the Layer window the opacity is displayed. Adjust it using a slider or by typing in a new value.

deleting: A layers can be deleted. Highlight the layer in the layer window and click the thrash icon, or drag it to the trash icon, or right click the layer in the layer window and select Delete Layer.

duplicating: A layer can be duplicated by right clicking it in the layer window and selecting Duplicate Layer…. Alternatively the layer can be dragged in the layer window down to the "Create a new layer" icon.

blank new layer: Pressing ⇧⌘N or clicking on the "Create a new layer" icon creates a blank new layer. It is inserted above the layer that currently selected.

new layer from pasting: Pasting into the canvas with ⌘V or Edit | Paste puts the copied pixels in a new layer above the layer that is currently selected.

new layer from vector tool: The type tool and the various shape tools create vector images instead of pixel images. The images are always placed in a new layer.

rasterizing a layer: If you try to draw on a layer with vector graphics in it using one of the pixel manipulation tools, such as the brush tool, eraser tool, fill bucket tool, you will see the no symbol when you move the pointer over the canvas. The graphics in the layer can be converted to pixels with Layer | Rasterize | Layer.

grouping layers: to group layers, select them in the layer window and use ⌘G or Layer | Group Layers. The layers must be adjacent. To ungroup layers, select them and use ⇧⌘G or Layer | Ungroup Layers. Notice that the component layers can be expanded or contracted by clicking the angle toggle in the group layer name. The group layer can be given a name.

merging layers: to merge layers, select them in the layer window and use ⌘E or Layer | Merge Layers. Often it is better to group than to merge, but use of some tools such as the eraser tool or fill bucket tool might require you to merge pixels to single layer.

background: When an image is opened in Photoshop, it is placed in a locked layer called the background layer. It is necessarily the bottommost layer—new layers are added above it. The opacity cannot be changed from 100%. Changing the name of the layer from "Background" to something else converts it to a regular layer. Usually one will want to duplicate the background layer to edit it, since it is useful to preserve the original image.

Paths

The pen tool and its variants are used to draw paths.

Paths appear in the Paths window, which is often a separate tab in the same pane as Layers window. By itself drawing a path puts nothing in the final image. At the bottom
are the icons "Fill path with foreground color" and "Stroke path with brush".

The pen tool is harder to use than its variants. You can practice using the pen tool at http://bezier.method.ac/. If you want to draw a polygonal path with the pen tool, click on each of the vertices without dragging.

The curvature pen tool can be used to create a smooth curve by clicking at points along the curve without dragging. To create a polygonal path, double click at the points.

Selecting

quick selecting: The quick selection tool is used by clicking and dragging. A single contiguous region will be selected. One can select an additional disjoint region by making sure the "Add to selection" button is selected and then clicking and dragging again. One can select the "Subtract from selection" to remove from the area that is already selected.

selecting subject: In Photoshop CC 2018, the menu item Select | Subject was added, which attempts to select the subject in a photo. If it doesn't do a perfect job, the selection can be modified with the quick selection tool.

selecting with magic wand: The magic wand tool selects a contiguous area which has the same brightness—the V of the HSV—of the selected pixel. Like the quick selection tool, there are buttons for adding and subtracting from the selection.

deselecting: Use ⌘D or Select | Deselect

inverting: Invert the selected region with ⇧⌘I or Select | Invert. The visual distinction between a selected region and its inverse is subtle. One of them will put selection boundary markers on the boundary of the image.

drawing a selection: the lasso tool or the pen tool can be used. The pen tool and its variants enable selecting a region with smooth borders precisely. These tools create a path which can be converted to a selection region by clicking the "Load path as selection" icon at the bottom of the Paths window when the path is selected.

using a shape to select: the rectangular marquee tool and the elliptical marquee tool can be used to select rectangles and ellipses. Hold the shift key while dragging to select a perfect square or circle. When you are finished dragging to determine the size, the tool converts to a mode which allows you to drag the selected region to a new location.

copying: once a select region is created, select the layer to copy from and type ⌘C or Edit | Copy.

auto-selecting: the move tool can be thought of as performing a selection. By default it selects everything in the topmost layer with a visible pixel at the point selected. If the "Auto-select:" dropdown is changed from "Layer" to "Group", the move tool will select the topmost group with a visible pixel at the point selected.

Masks

clipping masks

Select a region in the canvas. Select a layer in the Layer window. Click the "Add a mask" icon at the bottom of the Layer window. If a path was used to create the selected region, the tooltip text for the icon at the bottom of the Layer window is "Add a vector

adjustments

To convert a color image to black & white, select the image layer and then click:

Color | Adjustments | Black & White

To only convert a portion of the image, one could select that portion of the image with the marquee or lasso tool. However, usually it is more appropriate to select the region with the quick selection or magic wand tool.

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