GoalExplain layers and masks using sheets of tracing paper and paper cut-outs.
New words
layer · one transparent sheet in a stack that makes up a picturebackground · the bottom layer, behind everything elsemask · a cover that hides parts of a layer without erasing themtransparent · clear enough to see through
Explanation
Photo editors use layers. Imagine sheets of tracing paper piled on a table. On the bottom sheet you draw a desert: that is the background. On a sheet above it you draw a camel. On the top sheet you draw the sun. Where a sheet is empty you see through it to the sheets below, so together they make one picture. The great thing is that each sheet can be changed alone: move the camel, and the desert stays safe. A mask is like a paper cut-out laid over a layer. It hides the parts you cover and shows the parts you leave open. Hiding is not erasing: the picture is still under the mask, so if you made a mistake you can uncover it again. Blending two pictures often means putting one above the other and masking the parts you do not want. Steps differ in each program, so ask your teacher; here we understand the idea.
Worked examples
Sheet
What is drawn
top
a bird
middle
a tent
bottom
a green field
Stacking. The bottom sheet is a green field, the middle sheet has a tent and the top sheet has a bird. Looking from above you see all three together as one picture.
move only the top sheet→bird flies higher→tent and field stay
Changing one layer. Malak wants the bird to fly higher. She moves only the top sheet. The tent and the field do not move. If all the drawings were on one sheet she would have to redraw everything.
A mask. A paper cut-out with a round hole is laid over a photo of a street. Only the part in the hole shows. When Youssef lifts the paper, the whole street is back, so nothing was erased.
Class activity
Paper blend. You need two sheets of tracing paper or clear plastic and coloured pencils. On one sheet draw a background, for example the Nile at sunset. On the other draw something that does not exist there, for example a giant balloon. Lay the second sheet over the first and look at the blended picture. Cut a paper mask to hide a part of the balloon, and lift it again to show that nothing was erased.
Practice
1
What is a layer?
One transparent sheet in a stack that makes up a picture.
2
Which layer is the background?
The bottom layer, behind everything else.
3
Why is it useful to draw each thing on its own layer?
You can change one thing without changing the others.
4
A mask hides part of a layer. Is that part erased for ever?
