Photoshop Manual: Lasso Tool using Quick Mask

The Lasso Tool can be used for a loose, general selection or for a very precise selection.

For this part of the Photo Shop tutorials, open image number 05.jpg and select the Lasso Tool from the toolbox.
The cursor changes appropriately.
Draw a loose selection around the goldfish, as illustrated.
Beginners often find the Lasso Tool a bit tricky at first but practice soon pays dividends.

To help make the selection accurate, we'll use the Quick Mask Mode.
Click once on the Quick Mask Mode icon in the toolbox.
A red mask appears inside the selection. Red is the default colour but as it is a bit similar to the orange of the fish, it would be more convenient to have a colour which gives a better contrast.

Double-click on the Quick Mask Mode icon. Click on its colour box to bring up the Color Picker where you can choose a strong blue colour. It should still be distinguishable from the blue water. Click OK.
The Quick Mask Options palette now displays the chosen blue. Leave the opacity at 50%. Click OK.
The mask on the image is now blue and
it is easier to see the fish's outline.

Select the Brush and choose a hard brush from the top row in the Brushes palette. We'll use 100% hardness here and put on a feather afterwards. The colour boxes in the toolbox will now be black and white and as we are going to erase we want white to be on top.If white is not on top, then press X.
Zoom in on the image to increase its magnification.
A quick way to increase the view to 100%
is to double-click on the Zoom Tool in the toolbox.
Carefully use the Brush to erase the blue mask along the edge of the fish. For large open areas, a large brush is useful, but a smaller brush is required for small tight corners.
A shortcut to increase the Brush size by one step is to press the square bracket key, ].
Pressing the other square bracket key [ reduces the brush size by one step.
If the erasing brush goes over the edge of the fish, press X, which reverses the foreground and background colours. Then paint back in that part of the mask.
When the whole edge is accurately outlined, just the fish will be covered by the mask.
Select Standard Mode in the toolbox or press Q and the 'marching ants' will surround the fish.
Choose Select > Feather and a feather of 1.
Press F7 to show the Layers palette. We'll put the fish on a new layer by going to Layer > New > Layer via Copy.
Go to Select > Deselect. The fish is now its own transparent layer above the background.

Photoshop Manual