Layers, Channels, Transparency

[anon_private]

(02-03-2017, 06:08 PM)Ofnuts Wrote:

(02-03-2017, 05:45 PM)anon_private Wrote: Thank you for responding. You say

Quote:'The alpha-channel is a fourth image component (besides the R,G,B ones) that controls the opacity of the pixel. You don't choose a color to be transparent. A pixel is transparent because its alpha value is 0, whatever the R,G and B values. A pixel can also be partially transparent if its alpha is less than 1.

If I cannot choose to make a colour transparent. How would I make the background transparent?

If you want to delete a specific color and replace it with transparency, two completely equivalent techniques:

1) Colors>Color to alpha and pick up the color of the background

or

2) Bucket-fill the image with the background color after setting the bucket-fill tool in  "Color erase" mode

Both techniques require an alpha channel in the layer: Layer>Transparency>Add alpha channel

Both techniques have a side effect, if there are parts of your subjects with colors close to the color of the background, they
will become (partially) transparent as well. So before applying the above techniques you can restrict their action to the background and also
to the very important anti-aliasing pixels:

- using the wand, select the background
- Select>Grow by two pixels so that the selection includes the border pixels
- Apply Color-to-alpha or Color-erase as above.


Thank you.

After making adjustments to an image can I view it as it would be seen on a webpage, or, must I upload it to a site to complete the test?

Best wishes

Ps. I am using gimp 2.8.10 under kubuntu (14.10). Would you advise installing version 2.8.20, or, is there little difference between the programmes? My pc is a Dell Dimension E520, 1GB RAM, Pentium D (2.7GHz).