Advanced Graphics Editing Tutorial: Selections and Masks

Selections

We can use selections to isolate the edits that we make and to cut parts of an image out. Most image editing software has multiple ways to select. 
pixlr selection tools 

First is the Marquee tool. We can use it to select various shapes in an image, a rectangle or ellipse. The various options are

  • Constraint: 
    • No restriction: draw any rectangle you like
    • Aspect ratio: choose the proportions of the rectangle, Width:Height, like 4:3
    • Fixed size: choose the pixel dimensions, Width:Height, like 600:100
      Note: this is not like the crop tool's output size constraint.
  • Feather: this allows for hard edges, no feathering, or soft edges, feathering is greater than zero. Feathering allows the selection to fade out on the edges.

Next is the Lasso tool. We can use this to make custom shapes.

Last is the Magic Wand tool. It uses a fancy algorithm to select similar pixels.

  • Tolerance: 0 to 255. 0 selects only identical pixels and as you increase to 255 the pixels are less similar. 255 selects all.
  • Anti-alias: smooths the edges
  • Contiguous: connected
  • Tutorial Page Links to an external site.

Other selection options are available from the Edit menu.

  • Select all: selects the entire image
  • Deselect all: selects nothing
  • Invert Selection: switch to whatever was not previously selected
  • Select pixels: like select all but ignores and any transparent selection of the layer

Often, you must use select all or deselect all to do any editing outside of a selection. 

an image of a dog a transparent image of a dog a selection outside of a dog a dog, inverse selection, colorized a dog masked 

Here is an excellent video on using the different selection tools and options in the Pixlr Editor:

Pixlr Editor Selections Links to an external site.

Masks

Masks are a more sophisticated way of editing within a layer. A mask is a special kind of selection, gray scale images that represent selections. Masks give us more options for creating and editing these selections. Although they are a bit trickier than selections, they give us a bit more power. When masking, the paint brush tool allows you to paint visibility and the eraser tool allows you to paint invisibility.

You can create a layer mask in Pixlr from the Layers menu or the Layers window. Although you can make a mask in any layer, we often make a copy of the layer first. One benefit of a layer mask in Pixlr is that it saves the selection for reuse.

Pixlr Layer Mask Window screenshot of an image mask

Here is an excellent video tutorial on using Masks in Pixlr Editor. Please check it out.
http://ww2.kqed.org/education/2015/04/16/using-layer-masks-in-pixlr-editor/ Links to an external site.

You can consider Pixlr a scaled down version of Photoshop. The following article, although about Photoshop, has some great lessons about layers:
http://designshack.net/articles/graphics/a-complete-beginners-guide-to-masking-in-photoshop/ Links to an external site.