• A layer is basically transparency stacked on top of one another
• Layer features are available in Layer Panel @ top right which is also dockable
• When you open a image, a new layer will be created. Everything you will do on GIMP is doing through layers
• By default, this layer does not have a transparency on it. To add transparency, in the Layer Panel:

# Add transparency to image
Right click > Add Alpha Channel

◇ When you erase something off the image, you can see the checker board items and this represents transparency in your image
• The numbers of layers that you can use depends on the amount of your system memory
Stacking Order: The layer on the top will be displayed over whatever layer is below it
• To keep the layers intact, save the image as .XCF (GIMP native format)
Layers can be of different sizes. They're not always the same size as the composition. The size of a layer is indicated by orange and black dotted lines
• To make the layer the size of the entire composition

# Re-size layer to size of compoition
# From pull-down menu
Layer > Layer to Image Size
# or
Layer > Scale Layer


Add a New Layer

• There are several ways to add a new layer to an image:
◇ Click icon “Create New” at the bottom of the Layer Panel


◇ Open another file, drag and drop the file into the Canvas
◇ Copy and Paste an image into another image


The Layer Panel



Transform Lock

• Group the layers together so that when you use a tool like Scale tool, you can apply the scale all layers that are grouped. Also good for animating gifs
• To minimize quality loss when using transform tools, use interpolation NoHalo / LowHalo

# Reduce quality loss (Transform tool)
Tools Options > Interpolation > LowHalo
# or
Tools Options > Interpolation > NoHalo


Opacity Slider

• Adjust transparency of the layer


Layer Mode

• Available in 2.10 and above. Drop down dialog
• Layer mode is used to create blend mode so the layer on top can blend with the layer(s) below
Layer Mode Examples
◇ Soft Light
▪ Add layers in Orange creates warming effect. Blue creates cooling effect. and use Layer Mode “Soft Light”. You can adjust the effect with Opacity Slider as well
◇ Screen
▪ Get rid of all black pixels or the darker pixels. A quick way to get rid of the black background


Lock Features

• Lock the layers so you can't edit them. Different from Transform Lock
• Found in Layer Panel
◇ Icon “Lock Pixels”: can't paint
◇ Icon “Move Lock”: can't move the layer
◇ Icon “Lock Alpha Channel”: block editing of alpha channel (transparency) e.g. can't user eraser to erase the layer


Layer Group

• Click and drag multiple layers into a layer group
• Good for Web Page design
• Can add its own Layer Mask and Layer Mode to a Layer Group
Layer Mode: try "Overlay"


Layer Mask

• Allows you non-destructively (reversible) edit a layer
• Can be applied to Layer Group as well
◇ Make changes apply to certain part of a image
◇ Make blending & fading effects with Gradient


White creates opacity
◇ Use Black Paint tool on white Layer Mask: Show layer below
◇ Use White Paint tool on white Layer Mask: Show current layer


Black creates transparency
◇ Use Black Paint tool on white Layer Mask: Show current layer
◇ Use White Paint tool on black Layer Mask: Show layer below
◇ Useful, used frequently
◇ Before using this option, use selection tool, when complete, hit enter
◇ Select this option and your selection will be shown in foreground while the rest of the layer below will be shown
Grayscale copy of layer
◇ Creates semi-transparent effect


Quick Mask


• A type of layer mask
• How to use:
◇ To activate Quick Mask, click the square icon at the bottom left corner of the Canvas or use shortcut key shift-q
◇ Use paint tool to select an area (red is the unselected part)
◇ Click the square icon again to turn it off
◇ Add Layer Mask “Selection”


Differences with PhotoShop

• Unlike PhotoShop, GIMP does not contain adjustment layers, which means the image adjustments are typically made directly on your image layer
• Unlike PhotoShop, GIMP will move any layer that you're hovered over, not just the active layer