On 23-Dec-2002, Robert L Krawitz wrote:

1) How do I create an image with an alpha channel (and set the value of the alpha channel)? This is specifically so I can test alpha channel handling in Gimp-print. Specifically, I want to move the alpha channel handling (and the color map handling, but that's a lot easier) out of libgimpprint and into the plugin.

file -> new -> fill type = transparent.

2) It appears that thumbnail images (via gimp_image_get_thumbnail_data) always contain an alpha channel (unfortunately, this isn't really what I want for (1)). Is there a reason this is the case, or am I missing something?

Ever convert an rgb image to rgba? All the alpha for every pixel = 1.0. Its probably the same thing here.

Hi,

Robert L Krawitz writes:

1) How do I create an image with an alpha channel (and set the value of the alpha channel)? This is specifically so I can test alpha channel handling in Gimp-print. Specifically, I want to move the alpha channel handling (and the color map handling, but that's a lot easier) out of libgimpprint and into the plugin.

the alpha channel isn't associated with the image. It's part of the layer so you basically create a new image, then create a layer with type=RGBA_IMAGE and add it to the image.

2) It appears that thumbnail images (via gimp_image_get_thumbnail_data) always contain an alpha channel (unfortunately, this isn't really what I want for (1)). Is there a reason this is the case, or am I missing something?

the reason is that the composite buffer in the core always has an alpha channel. The preview is created from this buffer and thus also carries the alpha channel. Actually it should make your life easier since you don't have to write code for the non-alpha case.

Salut, Sven