A layer's blend mode specifies how it is blended with the layers below it. To change a layer's blend mode, click on the respective layer and then open its Properties (via the Layers menu, the Properties button, or by double clicking the layer). The following dialog will be shown:
Not all blend modes are easy to understand in classic or intuitive terms, and because of this we recommend that you experiment and make use of the forum for asking questions and getting tips.
For this discussion the following two images will be used for the background layer and for the 1st layer that is placed on top of the background layer:
In the discussions below, the term composition will be used. This refers to the result of blending all of the layers below the current layer being discussed. The "final" composition is what you see on the screen while working with the image. However, for this discussion we need to refer to the composition as it is being composed, layer by layer.
This is the default and standard blend mode. Each pixel in the layer is blended with the composition depending on its alpha value.
Each pixel component's intensity is multiplied with the pixel value in the composition. The result of using this blend mode is always pixels that are darker than the original. White pixels have no effect and are thus effectively transparent.
Each pixel's color intensity is added to the intensity of the pixel values in the composition. This will always brighten pixels in the composition, except for pixels that are completely black which will be effectively transparent.
This blend mode has the effect such that dark pixels are made darker. Lighter pixels must be blended with other lighter pixels in order to remain bright.
This can be thought of as the opposite of Color Burn. Lighter pixels are kept light, whereas darker pixels must be blended with other dark pixels in order to remain dark.
This blend mode can be used for adding shiny objects or areas of light.
This is the reverse of the Reflect mode: it works the same as swapping the layer positions and using Reflect.
This is a combination of Screen and Multiply depending on the intensity of the layer pixel. For darker colors, this acts like Multiply. For lighter colors, this acts like Screen.
The counterpart to Additive blending. The layer pixel's intensity is subtracted from the composition pixel's intensity resulting in darker colors. Since this can produce a negative intensity, which is not possible to display, the absolute value is used. Thus, both "white minus black" and "black minus white" will both produce white. This is quite often useful when using the Clouds effect.
At first glance this seems similar to Difference, but it actually produces the opposite effect. Instead of making colors darker, it will make them brighter.
The lighter pixel of either the layer or the composition is used.
The darker pixel of either the layer or the composition is used.
This can be thought of as the opposite of the Multiply blend mode. It is used to make pixels brighter, with black being effectively transparent.
This is short for "exclusive OR", which is an advanced blending mode that is primarily used for image analysis and not for drawing or image composition.