DIS2105: More on Selections in Photoshop

Remember that you can save your selection at any time – if you don’t save it, the selection will be lost when you close the image. The image must be saved as a PSD file in order to save a selection.

• Once your selection has been made, keep it active (marching ants) and go up to the ‘Select’ menu and choose ‘Save selection’

 

• The ‘Save a selection’ dialogue box then opens up. Here you can name the selection.
• In the example below, this is the first selection being saved, so some options are greyed out.
• Once you have named your selection, hit ‘save’.
• If you create another selection, when you save it, you can choose to ‘add’, ‘subtract’ or intersect it with the selection you previously saved.

• Choose the selection you want to work with from the ‘channel’ dropdown, then specify what you want to do from the ‘Operation’ radio buttons.

Selecting edges with the Magnetic Lasso tool



The magnetic lasso tool will automatically create a path a long an edge, detecting changes in contrast to define where that edge is.

1. Open the ‘phonebooth’ image, and try an initial selection of the red phone box using the tool set to its default – click on the first point of your selection (let’s try and select the red phone boxes from the background), then release and drag the cursor around the shape. The magnetic lasso creates a path, following the edge of the phone box, detecting the edge due to the tonal difference between it and the background  – you will notice though, that you hit some problems with the white space behind some of the trees behind the phone box – the tool detects this white space as a similar tonal value and so includes some of the shapes in the leaves. See below (To get this screen shot I had to double click to make my path in to a selection):



2. To undo the previous anchor point, just hit the delete/backspace key. This will eliminate the most recent point. You can repeat the deleting until you are in a position that suits your selection and then continue.
3. The default options for this tool have a setting of ‘width’ set to 10, which you can see in the tool options – in the shot below, I have reduced this to 4 px:


4. 
The width refers to the area that is taken in to consideration by the tool when the path is being made – obviously, the higher this number is, the more potential there is for error if you are trying to make a selection against a busy background. Having a smaller value here means you have to be more precise in your dragging around the shape though.
5. To see the size of the area being taken in to consideration by the tool, hit the caps lock key and move the mouse very slightly. To reduce or increase the size on the fly (you may want to increase and reduce several time as you make your selection), use the left and right curly brackets respectively {} – The same way we reduce brush size.
6. You can also add your own anchor points with this tool – just click when you need your own point and release the click when you want the tool to do the work
7. While using the magnetic lasso, you can also click the mouse on a point and hold down option to revert to the plain lasso tool. Clicking the mouse on a point and then hitting option once will revert to the polygonal lasso tool. Click and release with the mouse to return to the magnetic lasso.

Image Transparency Selections

When you have a layer that contains transparency (ie, your object is floating on the grey and white checkered background), you can easily load a selection of the object by apple/control clicking on the thumbnail image of that object in the layers palette – note that this will not work unless you click right on the image in the layers palette, rather than the layer name.

Image Luminosity Selections


Using the Channels palette, you can make selections based on the luminosity of the tonal values of the image. This can then be used to create a variety of effects, for example, creating a split toned image.

1. Open the image called ‘Landscape, then open the channels palette
2. If you hold down apple/control and then click on the thumbnail image of the RGB layer in the channels palette, you will select the brightest areas of the image, and partially select the less bright areas
3. This is hard to visualize with the marching ants – so, to see this selection better, let’s make a mask and save it as a channel
4. With the selection still active, click the ‘Save selection as channel’ icon at the bottom of the channels palette – it’s the icon that looks like a grey square containing a white circle – you will then see what looks like a grey scale image, but what it really is, is a representation of the selection, where white is the fully selected area, black is the fully de selected area and grey is the partially selected pixels in between.
5. You can use this selection to alter the shadows or hilights of the image, or you can add a split tone, simulating what can be done with a lot more time and some chemicals in the photographic dark room.
6. To add the split tone, you first need to convert the image to black and white. To do this, go back to the layers palette, then go Image/Adjustments/Black and White.
7. Now go back to the Channels palette and you will see that eventhough the image is now black and white, it still has the three RGB channels – the colour has been removed, however the tonal values are still there.
8. Select the image hilights in the image by command/apple clicking on the RGB channel – this is where we will add a tonal variation.
9. Back in the layers palette, click the ‘New Adjustment Layer’ icon at the bottom of the palette – choose ‘solid colour’ from the options that appear.
10. This opens the colour picker – choose a warm yellow colour.
11. To now put a tone in to the shadows, reselect the selection of the hilights you just used, by going Select/Reselect. To now select the shadows, all you need to do is invert this selection – go Select/Inverse – the shadows are now selected.
12. Now, back at the base of the layers palette, click the ‘New Fill or Adjustment layer’ icon and choose solid again. This time, choose a very dark purple colour from the picker.
13. You can then edit the opacity of the adjustment layers to get the desired effect.