Feathering blurs the edges of a selection. The amount of blur is depends on the pixel value you set in the Feather box. The higher the pixel value, the further the bluring edge. This will result smooth cutting effect on the selected object.
This option force ratio on your selection. 1:1 is always perfect square, and 1:2 mean the height is always 100% greater than width.
This option force the selection always made in stated size. This is useful in many Web graphic design project.
Subtract from selection
Add to Selection
Let's talk about these 4 little icons , start from the left is New Selection, Add to selection, Subtract from selection and Intersect with Selection.
New Selection reset the marquee selection everytime you drag the mouse on the image. Add to Selection merge your previous selected image area with your current selecting image area, while Subtract from selection remove portion of your previously selected image area. Finally, Intersect with Selection will chose only the previously selected image area and intersect with your currently selecting image area, only the image area within the intersect area with be remain selected.
See the following sample selection. The sample on the left created with Add to Selection and the sample on the right created with Subtract from selection. Note that you can quickly access the Add and Subtract from selection function by holding Shift or Alt key. Where holding Shift key turn your marquee selection to Add and holding Alt key will turn your marquee selection to subtract mode.
Making elliptical marquee selection is no different from rectangular marquee selection. You can use Alt key to make the elliptical marquee selection from the center of the object. You can also make a perfect round circle marquee selection by holding Shift key while dragging the mouse.
To move, rotate or resize the elliptical marquee selection. Simply right click on the elliptical marquee and click Transform selection. The rest is similar to Rectangular Marquee selection.
Why make marquee selection?
Marquee Selection allow us to isolate portion of image for later image editing. When portion of image is selected, it can be apply filter effect, cut and paste into new layer, move, transform and painted independantly from the rest of the image.
To access the Marquee Tool, Press M. By default it will select Rectangular Marquee Tool, press Shift+M again it will change to Elliptical Marquee Tool. You can also access these tools from Tools Palette.
If you want to drag your selection from center outward instead of corner to corner, hold ALT key and drag the mouse from the center of the object you want to select.
If you want to make a perfect square rectangular marquee selection, hold Shift key while drag the mouse. Note that this can be combine with ALT key to make a perfect square marquee selection from center.
Note that you can refine you marquee selection by transforming the marquee selection. Right click on your marquee selection and select Transform Selection
You might notice there is a Free Transform option located above Transform Selection. It is for transforming the actual pixel content of the selection on the active layer, for transforming the marquee selection itself, select Transform Selection.
The following transformation control will appear around the marquee selected image area.
To move the marquee selection, simply drag within the transformation control. To resize the marquee, simply place the mouse cursor to the edge of the transformation control and drag it. To rotate the marquee, place the mouse little further from the corner of the transformation control until you see the mouse cursor change to rotate icon.