3) Resizing and Cropping

Image Resize: changes the size of the selected image.

Image Size: how much storage space the image consumes.

Dimensions: the height and width of the image.

Fit To: options to set the image to common dimension presets (e.g. A4, 4 x 6 inches)

Width & Height: change the height and width based on the number of pixels (pixels can be changed to other units of measurement via the drop-down menu)

Resolution: change the pixel per inch (PPI) resolution of the image.

Resample: image interpolation when rescaling the image. (i.e. when upscaling an image, an algorithm "adds" extra pixels to unknown areas based on the estimated values of existing pixels). It is recommended to leave resample on Automatic.

Canvas Resize: changes the size of the canvas in the document.

Current Size: the amount of storage space the canvas currently consumes; also includes the current dimensions.

New Size: the amount of storage space the canvas will occupy after the changes to the size is applied. The unit of measurement can be changed from centimetres to other measurements via the drop-down menu.

Relative: how much to add or subtract from the canvas relative to its current size.

Anchor: changes the anchor location of where the canvas is resized from.

Cropping

Select the Crop Tool (C) on the toolbar or press C.

Once the Crop Tool is selected, anchor points will appear in the corners and along the edges. Clicking and dragging these anchor points will move the crop. Areas within the crop border will remain, meanwhile, anything outside will be trimmed.

Before applying the crop, ensure that Delete Cropped Pixels is unchecked so the crop can be changed later if needed and is non-destructive.

4) Working Non-destructively

Smart Object

Smart objects allow nondestructive scaling, filter effects and camera raw edits to be applied to a layer while preserving the source content of the layer.

Right-click on a layer and select Convert to Smart Object to change the layer into a smart object.

An indicator that a layer is a smart object is the icon that appears on the layer's thumbnail.

Transform and filters can now be applied without affecting the source image.

Newly applied filters will be linked to the layer and listed under Smart Filter. Double-clicking on the filter in Smart Filter will allow the filter to be adjusted.

In the example screenshot below, a Gaussian Blur has been applied to the smart object layer.

The Smart Filter can be used as an ordinary mask to nondestructively select where the filter effects are applied to the layer.

Working on Separate Layers

Working on separate layers allows for flexibility in adjusting or redoing edits that have been made in the past. If mistakes were made, it allows the designer to make changes instead of restarting from scratch.

For example in the image below, the edits which cover up and remove the log are placed on a separate layer from the image source.

Original image:

Original image with another layer on top with edits that cover up the log:

Use Adjustment Layers

There are two ways to add filters to images in Photoshop which is via the menu (Image > Adjustment > Filters) or in the Adjustment Panel.

Menu (Image > Adjustment > Filters)

Adjustment Panel

Once an adjustment is added to a layer via the Menu, the adjustment is permanently applied to it, it cannot be changed again. However, when an adjustment is added to a layer via the Adjustment Panel, the adjustment is added as a layer. This allows designers to select the adjustment layer in the Layers Panel and make changes later.

In the image above, an exposure adjustment layer was added from the Adjustment Panel and has created a new layer. At the top of the image, the exposure settings for the adjustment layer can be tweaked.

Note: Adjustment layers will affect every layer below it in the layer stack. If you want the adjustment layer to only affect the layer below it, use a clipping mask.

6) Selection and Masking

Quick Selection Tool

Select the Quick Selection Tool (W) from the toolbar.

Left-clicking on the canvas will create "marching ants", which is a checkered border that highlights which areas of the canvas is selected. Every pixel that is within the marching ants border will be a part of the selection.

Hold Alt/Option and left-click on the areas of the canvas you would like to deselect/exclude from the selection.

Lasso Tool

Select the Lasso Tool (L) from the toolbar.

Hold left-click and drag around the area of the canvas you would like to select. Releasing left-click will end the lasso.

Rectangle Marquee Tool

Select the Rectangle Marquee Tool (M) from the toolbar.

Hold left-click and drag over the area of the canvas you would like to select, release left-click to end the marquee tool.

Masking

Masking allows you to select which parts of the image to show or hide.

Important: Black = hides, white = shows

Click on the Add Layer Mask icon in the Layers Panel to add a mask to the selected layer.

A layer mask will look like this:

Using the Brush Tool (B), paint on the mask to hide or reveal parts of the layer.

Note: make sure that you have the mask selected when painting on it. The mask will have a border overlay around the thumbnail indicating that it's selected. As shown in the image below.

In the example below, I've painting black on the mask to hide parts of the image.