Wednesday, November 3, 2010

Lasso selection tools in PSE

Photoshop Elements offers a plenty of ways to select any object and thus allow placing it over some other image or doing selective editing. However for a newbie, the different selection tools remain a mystery. It is initially difficult to understand when to use which tool. Through this tutorial, I will try to capture the use of the first set of selection tools which is the lasso group consisting of Lasso tool, Magnetic lasso tool and polygonal lasso tool. My subsequent tutorial will cover other selection tools as well.

Lasso tool 

Lasso tool is a free form selection tool which allows you to select any irregular shape by just mouse click and move the mouse over the edges of the object. The selection precision through this tool depends on how steady your hand movements are, along with the mouse sensitivity. So if your hand selection is steady and precise, you would get good results. Shortcut key for this tool is L.

This tool is present as highlighted in the toolbar image shown in the image on right.
As you start making the selection you would notice that it is hard to follow the thread edge of the lasso tool icon. So you can turn on your Caps lock key to make this icon appear as a normal cross hair icon which has a defined center.


So once you open the image in Editor, you just need to click on this tool icon and get started with your selection. Once you click and move the mouse the selection boundary will start getting drawn. As soon as you release the mouse, the selection area get closed by a straight line between you initial and final points.

  

So as seen in the image on left. I started my selection from point A across the curve side of the apple. I released the mouse at point B. As soon as I released the mouse, a straight line closed the selection to have an area selected as shown in the image.






For making better and smooth selections, here are the additional options in the top options bar which are provided with this tool :






The Yellow highlighted part of the image has four icons :

1. New selection : This is selected by default. This is for making new selection. If a selection
is already made with this option is selected and you start a new selection, the old selection disappears.

2. Add to selection : If there is some selected area already and you want to add new area to the selection, click on this icon and start the new selection.

3. Subtract from selection : If your selection area has some parts which are un-required and were mistakingly selection, you can choose this option and start selecting the area you want to subtract from the existing selection.

4. Intersection of the selections : If you have an area selected already and you want to have a new selection which has some parts of existing selection with some new area as well, just select this option after you have an existing selection and start selecting the new area.

The Orange highlighted tools in the image above are for smoothing and refining your selection. If none of these options are used, the selection will have jagged edges. This tools are common to other selection tools as well.

1. Feather : This option has a text field in which you can specify the amount in pixels. The value range is from 0-250 px. The large the value, smoother the selection. This edge smoothing method causes the edges of selection to be blurred causing the smoothing of the edges. Hence this method is accompanied with loss of image details across the edges. If the blur is too high, loss of data will also be high.

The effect of feathering is inversely proportional to the resolution of image in DPI. So a higher DPI image will have lesser effect of feather as compared to same feather applied on lower DPI image. Actually the formula is simple. Since a higher DPI image has more pixels per inch hence a 2 px feather will not be that much visible. But in an image where pixel density is low, 2 px feather will be visible very clearly.

Please note that this feather value must be given in advance before making the selection else this option would not be honored. To give feather to an existing selection, you can select the Refine edge button which we shall discuss shortly.

2. Anti aliasing : Unlike Feather option, this edge smoothing option is lossless and subtle. If this check box is checked before making a selection, the jagged selection edges will e smoothened as you go along with your selection. Instead of blurring edges as in case of feathering, it instead adds some gray pixel around the jagged selection boundary making it smooth and giving the squared pixel a curvy effect. So this is highly useful option which one should check with any of the selection tools.
This option is used for distortion less smoothing of edges.

3. Refine Edges : This is the next option in the options bar. As you click the button, you are shown with the following dialog. These options are used to refine the edges once you have already made the selection. The button remains disabled before any selection is present.


The options highlighted in green box are the sliders to refine the edges of the selection. The options in yellow box are for viewing the smoothing effect of the selection in the selected background or mask. The options in purple are for Zooming in, preview and move the image to view a specific area of the image.

You can select any of the icons in the yellow box to view your selection in different backgrounds or if you want to view it as a mask. You can either select lack, red or white background or view the selection as a mask. These options enable you look closely to judge how much refinements are still required.
I have chosen "On Black" which is third icon in the yellow box.


As from the above image, I can make out that my selection boundaries are very jagged, so i need to refine them. So I use the following options to achieve that :

1. The Smooth slider smoothen the edges without rounding the corners. I use it quite often as I do not visualize much destruction with this option. For this image I gave the value around 5.

2. Feather slider is same as the feather text box discussed earlier i.e. it adds the blur to refine the edges. The difference is that using this slider you can add feathering after you have made your selection unlike the option discussed above.

I added a feather of 0.8 for this selection.

3. Contract/Expand slider shrinks or expands your selection boundaries in parallel to your selection edges. You can use the slider to expand or shrink your selection until your selection boundary meets the edges of the object.

For this image, I contacted it by a value of -11.


Magnetic Lasso tool


It is an intelligent lasso tool(free form selection) with edge detecting capability. So it reads the color brightness change information along the edges and then the tool keeps sticking to the edges automatically as you move the mouse.
As you click over any edge of the object and start moving the mouse across the edge, it automatically detects your edges and follow the edges precisely as you move the mouse making the selection quicker.

It keeps adding anchoring points to the selection across as you move the mouse. In case if any inappropriate anchor point gets introduced in you selection, you can undo each anchor point by pressing Backspace key. Esc key will completely remove the selection.



To switch between different Lasso tools, you can press Shift+L. Same tip for this tool as well. You should turn on Caps lock key while making selection as it brings the cross hair icon for the selection instead of the thread part of the tool icon which is difficult to follow while making selection.

For a closed selection one should double click in the end where start and end points meet. With a single click, one can start the selection and move across the edges so that the selection line is drawn automatically with this tool and anchor points are also drawn. One can also introduce more anchor points to give more sharper selection by single clicking in between while moving mouse.

As shown in the image above, the points on the selection curve are the anchor points which define the selection.

Here are the options for magnetic lasso tool in the options bar :


The options highlighted in yellow box are same as described above for Lasso tool which are there to mark a new selection, add to an existing selection, subtract from an existing selection or get the intersection area of two selections.
The options marked in Orange box are there to control the smoothing of the selection and to decide how fast and accurate we can make our selection to be. The options Feather and Anti-aliasing are same as we described in Lasso tool. 

Width defines the radius of the cross hair cursor. The bigger the radius, the faster is the selection. However if the object to be selected and the background have lower contrast, it is advisable to keep the radius small for magnetic lasso tool to detect the edges efficiently. The value of this radius ranges from 0-256 px.

Contrast value in the Orange highlighted box decides how much sensitive our selection brush is with the contrast between our object and the background. So for low contrast between the object and the background, we should keep the percentage value of Contrast field to be low which would tell out tool to intelligently understand this input and work precisely for detecting edges. However if contrast is high, we should keep this value high to tell our tool to work faster as it does not have to make any deep calculations for detecting edges.

The text field Frequency defines the density of the anchor points. So for a sharper and precise selection, more anchor points can be drawn. The range of this option is 0-100. So if I specify the value as 100, here is how my selection would appear :


The value of Frequency should not be very high as it starts giving very jagged selection. Default value is 57 which works almost appropriately.

The tool in the green highlighted box is to control the pen pressure on the tablet (I have not used this option as I do not have a tablet).

Once you have started the selection using this tool, you may not be able to go to the options bar and change the values as required since it would disturb the selection. So one has to use the shortcuts to dynamically change the options in the options bar. (,) comma and (.) period are used to increase and decrease contrasts.

Magnetic lasso tool works very well most of the time when there are good contrasts between the object and the backgrounds. In case of contrast as well, it works well if the above parameters are set accordingly for low contrast like low width and low contrast value. However in cases when there are selections like selecting hair or fur or any specific colored objects etc where other tools work better which we would cover in other tutorials.

Polygonal Lasso Tool


This tool can also be found in the Lasso tool flyout menu below Magnetic Lasso tool. Once can select Shift+L to switch between this tool and other Lasso tool.

It is also for free form selection of any object or area when straight line edges are required. You can start your selection with single click which gives a start point, second click draws the straight line selection line which in turn connects to the third click with the other selection line.

To give an example of where I used it in one of the demos is when I had to clone the hay bundle as shown in the polygonal selection to its left.



I created a duplicate layer of the image(Control+J), then selected the grass bundle with the polygonal lasso tool as shown and then using the Move tool from the toolbar and move it to the area whre I need the clone.



As you can see from the image above, I have been able to clone the area as required.

Once you have made the selection using any of the selection tools, what else can you do with the selection?

As you can see from the image above, I have been able to clone the area as required.

- One can select "Layer via Copy" and create a separate layer of the object selected and edit that layer as required. One can hence independently edit this object layer as required. Like converting to black and white or enhancing colors of the objects etc.
- One can right click and "Select inverse" to select the areas apart from current selection and create a "Layer via Copy" from right click to create a separate layer of the background and edit the background as required. Like blurring the background or painting the background with a gradient etc.
- Create a copy of the background image. Select the area using any tool and use move tool to move this area to somewhere else in this image or some other opened image in Editor.
- Transform the selection via right click options and place it at necessary location in the same or the different image.




9 comments:

  1. What you have described under "Intersection" is actually the union of the two selections. Only the part that is common to both selections will be included.

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  2. Thanks for this, Vaishali, I found it very helpful.

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