Re: tinting transparency.

[William Robinson <airbaggins yahoo co uk>]

On Fri, 2004-10-15 at 04:08, Elijah Newren wrote:
> On Thu, 14 Oct 2004 14:31:42 +0100, William Robinson
> <airbaggins yahoo co uk> wrote:
> 
> > Also, the reason I want to have a hack at it is that I wanted to see if
> > I can make transparency work as a tint of the background colour with an
> > image (a-la aterm).
> 
> Why isn't
>   Edit->Current Profile->Effects->Transparent background
> good enough?  What are you doing that's any different than that feature?
> 
> 

Yes, I'm aware of this one. I would like an actual tinting filter with
the background colour like aterm has. It looks like gnome-terminal uses
a formula like (for each pixel r, g and b element):

background_color*background_darkness + image_colour*(1.0-background_darkness)

to derive the final background terminal image. But, I haven't yet got my
head around the vte/gnome-terminal code to be sure of this yet. I
understand that aterm uses a formula like (for each pixel r, g and b
element):

tint_colour * image_colour / colour_element_max

I believe the latter is more visually consistent and easier to read
paler coloured text on. It looks more like a coloured sheet of acetate,
a light filter, or a sweet wrapper would, if you put them over your
background image. Where colour elements are just being removed by the
multiplicative method it gives a more natural feel to the transparency,
I feel. I also feel that the mixing slider muddies up the image, where a
pure multiplicative tinting method can preserve the contrasts in a
background image, without sacrificing text readability. I've arranged
some screenshots to try and illustrate the differences:

http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal.jpeg
http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal-2.jpeg
http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal-3.jpeg
http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal-4.jpeg
http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal-5.jpeg
http://pix.hobbiton.cjb.net/bill/screenshots/aterm-vs-gnome-terminal-6.jpeg

Obviously, I'm not requesting/suggesting replacing the algorithm, but a
checkbox in the Effects tab of the Profile Editor to select the
behaviour would be great. 

I'm sorry if my terminology is not entirely accurate. I hope that you
understand what I'm getting at now. Maybe it seems petty, but i find
aterm's multiplicative transparency a lot more pleasant to work with
than gnome-terminals (additive?) transparency. 

What do you think?

-bill