Alpha Primer

Besides defining the transparency of an image by selecting a palette color entry you can also define alpha transparency.
Alpha transparency means that every single color pixel has an additional value that defines the opacity of this pixel. This alpha value may range from 0 (completely invisible) to 255 (fully visible). These alpha values are stored in a second layer. If you have a project with alpha then the transparency settings in the main form will turn to:

You can toggle if the color and alpha layers are to be shown or not and which layer you want to edit. Double click on a layer's edit function to switch the other layer off. If alpha is not set to be shown then all pixels are displayed fully opaque.

General Usage

Since Pro Motion is a software to edit indexed graphics based on color palettes, also the alpha layer uses a palette. The palette then containts the actual alpha values. By default a 1:1 relation is used, so that index 0 in the alpha palette uses alpha value 0 and index 255 uses alpha value 255. Depending on the settings for the alpha channel (see project settings) this alpha palette may contain other values, e.g. to match ceratin hardware limitiations for the alpha channel as to be found on GB DS/Nitro or PSP.
Because the alpha layer also has a palette you can use most color edit functions as if you would work with a color palette. But instead of modifying an RGB value you only have an alpha value that is displayed as gray scale from black to white. You may even use gradient filling or color cycling on the alpha layer to have special transparency effects.
By default the alpha layer uses a global palette. That means all frames use the same palette, modifying it in one frame will copy it to all other frames. You can changes this setting using the global palette "G" icon near to the layer controls.

Drawing with Alpha

There are two modes to modify the alpha layer data.
If you Edit (see button for the layers) the alpha layer then you draw directly into the bitmap of the alpha layer as you would do with the color layer. The color palette then turns to contain the gray alpha values. You can select a "color" there and draw it's value into the alpha layer bitmap which will make the corresponding color pixels to be more or less visible.

The other mode is to draw on the color layer while having the alpha layer set to be visible. You can then use an opacity value from 0 to 255 that defines how the transparency of the pixels are to be modified. The larger the opacity value to more opaque the pixels will become with every drawing step. This is the way how common drawing packages work with alpha.

File I/O

Usually palette based images can not be stored with alpha. To get around this problem Pro Motion will save additional files containing the alpha layer data as soon as you use a file type that can not carry alpha data. If you for example store your image as foo.pcx then a second file foo.alpha.pcx will be stored containing the alpha data. On load Pro Motion detects such an alpha file and reloads it into the alpha layer. Same works for animation.
There are some file types that support for alpha, but only if the color pixels are stored as 24Bit image layer, e.g. TGA or PNG. Such files can be stored, but remember that you possibly loose your palette order if you do so, because a color palette can not be stored into such 24Bit files. There is a special option in the project settings that will store the palette data as a separate file to keep it for the next load. But then you must carry this palette file with the image file!

Alpha Primer

General Usage

Drawing with Alpha

File I/O

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