Why does Output_Alpha=on not work in 3.7 when a background{} is specified?

Post a reply to this message

Le 30/12/2011 06:42, Cousin Ricky nous fit lire :
> Why does Output_Alpha=on not work in 3.7 when a background{} is specified?

Interesting question. Confirmed last night (I was thinking about asking
too!).

And it might be related to the kind of camera (I have tried alternative
type of camera (perspective, and other customs), including the same
scene, and for some +UA works, for other it does not. (these are camera
with a mask, like the omnimax one)

Post a reply to this message

Cousin Ricky <rickysttATyahooDOTcom> wrote:
> Why does Output_Alpha=on not work in 3.7 when a background{} is specified?

  I haven't tested it, but does your background have transparency in its
color map? Because I have this faint recollection that it was changed so
that if it has, it would end up in the final image as such (and consequently
if there's no transparency, no transparency would end up in the final
image).

-- 
                                                          - Warp

Post a reply to this message

> Cousin Ricky<rickysttATyahooDOTcom>  wrote:
>> Why does Output_Alpha=on not work in 3.7 when a background{} is specified?
>
>    I haven't tested it, but does your background have transparency in its
> color map? Because I have this faint recollection that it was changed so
> that if it has, it would end up in the final image as such (and consequently
> if there's no transparency, no transparency would end up in the final
> image).
>

Effectively, if I remember correctly, the background now need a filter 
or transmit value to allow alpha transparency.


Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> Effectively, if I remember correctly, the background now need a filter
> or transmit value to allow alpha transparency.

Thanks, that works.  I guess it hasn't made it into the documentation yet.

Post a reply to this message

On 31-12-2011 5:30, Cousin Ricky wrote:
> Alain<aze### [at] qwertyorg>  wrote:
>> Effectively, if I remember correctly, the background now need a filter
>> or transmit value to allow alpha transparency.
>
> Thanks, that works.  I guess it hasn't made it into the documentation yet.
>

It seems not indeed, or not clear enough. In section 3.1.2.4.1 Output 
File Type, the relevant paragraph reads (text put between * * by me):

[quote]
The alpha channel stores a transparency value for each pixel, just like 
there is also stored a value for red green and blue light for each 
pixel. In POV-Ray, when the alpha channel is turned on, *all areas of 
the image where the background is partly or fully visible will be partly 
or fully transparent*. Refractions of the background will also be 
transparent, but not reflections. Also anti-aliasing is taken into account
[/quote]

In highlighted phrase filter and transmit should be mentioned explicitly.

Thomas

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> Effectively, if I remember correctly, the background now need a filter
> or transmit value to allow alpha transparency.

Except that anti-aliasing doesn't appear to work properly.

Post a reply to this message

On 12/31/2011 02:56 AM, Thomas de Groot wrote:
> On 31-12-2011 5:30, Cousin Ricky wrote:
>> Alain<aze### [at] qwertyorg> wrote:
>>> Effectively, if I remember correctly, the background now need a filter
>>> or transmit value to allow alpha transparency.
>>
>> Thanks, that works. I guess it hasn't made it into the documentation yet.
>>
>
> It seems not indeed, or not clear enough. In section 3.1.2.4.1 Output
> File Type, the relevant paragraph reads (text put between * * by me):
>
> [quote]
> The alpha channel stores a transparency value for each pixel, just like
> there is also stored a value for red green and blue light for each
> pixel. In POV-Ray, when the alpha channel is turned on, *all areas of
> the image where the background is partly or fully visible will be partly
> or fully transparent*. Refractions of the background will also be
> transparent, but not reflections. Also anti-aliasing is taken into account
> [/quote]
>
> In highlighted phrase filter and transmit should be mentioned explicitly.
>
> Thomas
>
>
After re-reading the section, I guess a little clarification wouldn't 
hurt. The highlighted section you mentioned has been changed ... also 
found the same "Note" here: 
http://wiki.povray.org/content/Documentation:Reference_Section_5#Using_the_Alpha_Channel

and changed it there too! Thanks everyone.

Post a reply to this message

Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> In highlighted phrase filter and transmit should be mentioned explicitly.

Yes, that would be helpful.  Thanks.

Post a reply to this message

On 12/31/2011 08:23 AM, Cousin Ricky wrote:
> Alain<aze### [at] qwertyorg>  wrote:
>> Effectively, if I remember correctly, the background now need a filter
>> or transmit value to allow alpha transparency.
>
> Except that anti-aliasing doesn't appear to work properly.
>
>
look at the bottom of this section:
http://wiki.povray.org/content/Documentation:Reference_Section_1.3#Anti-Aliasing_Options

perhaps the problem you are seeing can be mitigated by specifying +AG1.0 
which effectively gives neutral behavior ... 2.5 is the default. Haven't 
tried this ... maybe for a shot ;-)

Post a reply to this message