Selecting through the Alpha channel
When stacking layers, Autograph builds a selection map based on both the position of each element in the stack from bottom to top, and each layer’s Alpha channel. This allows you to select the elements you actually see in the Viewer, without worrying about layer bounding boxes and transparent pixels that might prevent you from selecting a visible element. Clicking within the Viewer will go through the Alpha channel of each layer to eventually reach a pixel with an opacity higher than 0.5, and select the corresponding layer.
This selection takes into account transparency after applying modifiers such as a Color Difference Key, used to remove a green screen.
When you move your mouse over the Viewer and the cursor enters an area of this selection map, a flash appears on the layer that will be selected if you click it. A yellow outline defines the selected layer(s). It’s possible to add new layers to the current selection by pressing the SHIFT key and clicking on them.
Blending modes and selection map
The Alpha channel is not the only factor used when creating the selection map. The layer blending mode used also defines areas through which the click can pass through.
In the following example, a dust image without an Alpha channel is added to the top of the stack in Screen mode. The dark parts let you see the rest of the stack while the brighter parts hide it.
The Screen mode considered the black parts as transparent and Autograph takes this into account when creating the selection map. So it’s possible to click through these disappearing black parts to select lower layers in the stack. This selection is accurate to the pixel. By moving your mouse over the parts of the dust where the relative transparency is higher than 50%, you can select the dust layer by clicking it.
Selecting based on bounding boxes
For layers containing very thin elements such as text, the transparency-based selection may not be very convenient. Autograph provides a selection mode based on layer bounding boxes instead, which is available in the top bar of the Viewer.
This selector contains two modes:
- Select with Alpha channel (default)
- Select with bounding box
In this second mode, the selection map is made from the full bounding boxes, without checking transparency.
In order to select layers more easily, especially those hidden behind others, you can also rely on the Visual stack.
Connecting to the Timeline
When hovering over a layer, it lights up in the Timeline at the same time so you can see its position in the stack.