Photoshop - basic image actions

Before doing any action in Phtotshop, you need to select the correct layer to work on.

How to select a layer

1. Use the Select drop down menu and choose all layer OR

2. Click on them in the layers tab.



Once you have selected a layer, you need to choose which part of the image on that layer to work on

How to select a whole image

• Use a selection tool: Click once to select; click again to deselect  OR
• Use a keyboard shortcut: the fastest whole-image selection, is Ctrl+A (Windows) or command+A (Mac).  OR
•  Use menu command: Selection > Select All (or similar - may chancge between versions)

Note: other useful items on the Selection menu: Select None or Deselect (Ctrl/d) that turns off an existing selection.

Use one of these tools to select part of an image:

• Lasso
• Polygonal Lasso
• Magnetic Lasso
• Elliptical Marquee
• Magic Wand
• (and more?)

Note that once you have selected the tool, you can see its options bar - tools have different options.

Properties of the Selection tools 

The Lasso, Polygonal Lasso, Magnetic Lasso tools are hidden in the Toolbox under one and the same icon. The icon on the Toolbox displays the last selected tool. Use the floating menu to choose one of these others. To access it, right-click on the arrow in the lower right corner of the displayed icon.

The Lasso tool 

This is useful for drawing freeform segments of a selection Select the Lasso tool, and set feathering and anti-aliasing in the options bar. (See Soften the edges of selections.), and then use the mouse to draw the border of the area.

The options bar has selectors for a new selection, or

• add to,
• subtract from,
• intersect with

the existing selection.


With the Lasso tool, you can:

• Drag to draw a freehand selection border.
• Switch between freehand and straight-edged selection by pressing Alt (Windows) or Option (Mac).
• Click where segments should begin and end.
• Erase recently-drawn straight segments by pressing the Delete key.
• Close the selection border by releasing the mouse without holding down Alt (Windows) or Option (Mac).
• Optional - Click Refine Edge to adjust the selection boundary.

To use the Lasso tool

• Select the tool
• Click at the first point of the area to be selected using the left button
• Left-click at points around the area, to outline it.

The Rectangular marquee tool

This is used to select rectangular and square areas.

• Activate it by clicking on the icon or select it from the floating window.
• Put the mouse cursor where the corner of an imaginary rectangular should be, and press the left button.
• Keeping the left button pressed, move the cursor to the diagonally-opposite corner
• Release the button.

To select a square area keep the SHIFT key pressed while selecting. But remember that this will also add the new selection to any existing selection.

The Elliptical marquee tool 

This is used to select ellipses and circles.

• Select the Elliptical marquee tool from the Toolbox by clicking on the icon or select it from the floating window.
• Put the cursor at the point where the corner of an imaginary rectangular with an inscribed ellipse should be
• Press the left button.
• Keeping the left button pressed, move the cursor to the diagonally-opposite corner
• Release the button.

Select a circular area by keeping the SHIFT key pressed. But remember that this will also add the new selection to any existing selection.

Alternative: hold the Alt (Windows) or Option (Mac) key while when selecting an elliptical or a rectangular area, and the selection is made from the center to borders, instead of corner to corner.

The Polygonal Lasso 

This is also used to make freehand selections, but the contour of the selections is made up of straight segments. To use it:

• Select the Polygonal Lasso tool
• Put the cursor on any point that is to be part of the outline,
• Click the left mouse button, to mark the first point of the contour.
• Move the cursor an adjoining point of the contour and left-click it: a straight-line selection will be made between the two points.
• Repeat the previous step until the 2nd-to-last point is made.
• Click on the first point (which is also the last point) again to close the contour.

The Magnetic Lasso 
This is also used to make a freehand selection, but you don't have to follow the contour of the object precisely: any object that stands out against the background of the selected area is traced automatically when you move the cursor along the object. To use it:

• Select the Magnetic Lasso tool
• Put the cursor on any point on the edge of the object to be selected
• Hold down the left button and start dragging the cursor along the object. Fastening points will appear as you outline the object and when you make a click. If a one is irrelevant, remove it by pressing the DELETE key and return to the previous fastening point to continue outlining the object.
• Close the contour by joining the first fastening point to the last one by bringing the cursor to the first point or by making a double-click.

The Magic Wand tool 

This elects a consistently coloured area.  The options bar has a place to set the Tolerance - for this, the higher the tolerance, the more colours will be selected with a single click. Valid values are 0 to 255:  0 means only one colour is selected, 2255 means all colours in the image will be selected.

To use it:
1. Select the magic wand tool.
2. Move the cursor to a pixel which must be in the selection and left-click. 
When you do this, an outline ("marching ants") appears around the pixel, and all other pixels in image with a similar colour, within the specified Tolerance value.

These selection tools are efficient due to the flexibility of their usage: you can add to, subtract from or intersect a selection.

• Add by holding the SHIFT key.
• subtract by holding the Alt (Option in Macintosh) key 
• Intersect by holding the SHIFT and Alt (Shift and Option in Macintosh) keys 

 while selecting more pixels with the "same" colour.

Invert a selection

Inverting a selection swaps the currenly selected and unselected areas  (so currently unselected becomes selected)

Use it from the menus, by choosing Select > Inverse.

Hint:  this is the easiest way to select an object which is set against a solid-colored area:  just select the solid colour with the Magic Wand tool, and the use Select > Inverse.

Softening the edges of a selection

There are two techniques for this.

Anti-aliasing smooths the jagged edges of a selection by softening the colour transition between edge pixels and background pixels. Only the edge pixels change, so no detail is lost. This technique is useful when cutting, copying, and pasting selections to create composite images.

Anti-aliasing is available for these tools:
Lasso
Polygonal Lasso
Magnetic Lasso
Elliptical Marquee
Magic Wand


You need to specify anti-aliasing before using the selection tool -  you cannot add it after selection.   Therefore to use it:

1. Select the tool.
2. Select Anti-aliased in the options bar.
3. Select the area to be anti-aliased.

Feathering blurs edges by building a transition boundary between the selection and the surrounding pixels. This may cause some loss of detail at the edge of the selection. 

Feathering is available for these tools:

• Marquee
• Lasso
• Polygonal Lasso
• Magnetic Lasso tool

Feathering effects only show after you move, cut, copy, or fill a selection.   So to use feathering

1. Select a tool.
2. Enter a Feather value in the options bar. (from 0 to 250 pixels)
3. Select the area to be feathered
4. CHECK - IS THIS WHERE YOU NEED TO CUT/COPY AND THEN PASTE?

To define a feathered edge for an existing selection
1. Choose Select > Modify > Feather.
2. Enter a value for the Feather Radius, and click OK.

Issues with feathering:
A small selection made with a large feather radius may be so faint that its edges are invisible and therefore not selectable. If you see the message “No pixels are more than 50% selected,” either decrease the feather radius or increase the size of the selection. Or click OK to accept the mask at its current setting and create a selection in which you cannot see the edges.