POV-Ray : Newsgroups : povray.general : a note about using Output_Alpha Server Time
29 Feb 2024 19:25:21 EST (-0500)
  a note about using Output_Alpha (Message 1 to 6 of 6)  
From: Kenneth
Subject: a note about using Output_Alpha
Date: 12 Feb 2023 09:25:00
Message: <web.63e8f56a640da1fb9b4924336e066e29@news.povray.org>
The documentation at     3.2.4.1 Output File Type   says,
"Note: In version 3.7 alpha handling for image file OUTPUT has changed.
Effectively, the background *now requires* a filter or transmit value in order
for alpha transparency to work properly...The philosophy of the alpha channel
feature in POV-Ray is that the background color should not be present in the
color of the image when the alpha channel is used..."

So even for quick tests of using Output_Alpha (or +ua) to make a .png
alpha-channel render, I have always dutifully added at least a
background{rgbt 1} statement to a scene-- because I thought at least *something*
was required there.

But if there is no background *at all* in a scene, Output_Alpha can be used by
itself and still work correctly. Duh.

I must have been mis-reading the docs all this time...although the 'requirement'
statement is a bit misleading, IMO. Or a little tidbit of clarifying info was
overlooked.

You would think that, at *sometime* in the past, I would have made a mistake
writing even a simple scene and discovered this little fact by chance. But no.
:-(

Anyway, I learned something new...today!


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From: Bald Eagle
Subject: Re: a note about using Output_Alpha
Date: 12 Feb 2023 10:00:00
Message: <web.63e8fe61a721fd51f9dae3025979125@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:

> But if there is no background *at all* in a scene, Output_Alpha can be used by
> itself and still work correctly.

Having gone over this topic quite a few times in the past, that was the way that
I currently understood it - _NO_ background.
searching for "transparent background" yields:
About 419 results


It has been suggested that we ought to have a "sticky note" section of the
forum, where we can have useful things posted and whole archives - Mike
Williams, Friedrich Lohmueller, etc.  Dunno if we have a FAQ or what state it's
in.

Anyway, in the absence of that, I usually write often-used and often-forgotten
code snippets into my own directory in the Insert Menu.
Because working code examples always trump any documentation. (at least in the
short term)

Perhaps it would be useful for folks to start a new thread on their favorite
code snippets, and we could assemble them into a nice little .zip file of text
documents in a Frequently Used Code Compilation.  Then it would all be right
there in a handy drop-down menu.


Because sometimes even we long time users need to reference
Frequently Used Code. QED.


- BW


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From: Kenneth
Subject: Re: a note about using Output_Alpha
Date: 12 Feb 2023 10:40:00
Message: <web.63e90760a721fd59b4924336e066e29@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
>
> Having gone over this topic quite a few times in the past, that was the
> way that I currently understood it - _NO_ background.
> searching for "transparent background" yields:
> About 419 results

Duh. :-(

I didn't even bother doing a search-- 'cause I thought I had discovered
something Earth-shattering, ha. Or that someone *may* have mentioned it in the
distant past-- maybe once-- but that it was buried in some obscure post. Mea
culpa.
>
>
> It has been suggested that we ought to have a "sticky note" section of the
> forum...

... or stuck to my monitor...along with 1000 others...
>
> Anyway, in the absence of that, I usually write often-used and often-forgotten
> code snippets into my own directory in the Insert Menu.

A fine idea-- as is your encyclopedic spreadsheet. I have a tendency to find
these things out while working on an 'unrelated' scene or idea...side-tracked,
in other words...but then my new-found 'eureka' tidbits of knowledge remain in
gobs of scene files where they began :-(  But I DID make a demo scene of THIS
little tidbit :-D

Now it's 420 results...


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From: Kenneth
Subject: Re: a note about using Output_Alpha
Date: 12 Feb 2023 11:05:00
Message: <web.63e90ccba721fd59b4924336e066e29@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
>
>
> ...I usually write often-used and often-forgotten
> code snippets into my own directory in the Insert Menu.

The big question everyone wants to know is...do you ever sleep??!

With all the neat and complex things and ideas that you come up with, I figure
that there must be multiple copies of Bald Eagle situated throughout the world,
all working massively in parallel. The Nvidia Networked Bald Eagle GPU!

However you do it, don't change! ;-)


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From: Bald Eagle
Subject: Re: a note about using Output_Alpha
Date: 12 Feb 2023 13:10:00
Message: <web.63e92aada721fd51f9dae3025979125@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
I have a tendency to find
> these things out while working on an 'unrelated' scene or idea...side-tracked,


Me too.

I just accidentally founf that you can include a file just by using the name
without the extension.  :)


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From: Bald Eagle
Subject: Re: a note about using Output_Alpha
Date: 12 Feb 2023 13:20:00
Message: <web.63e92cc1a721fd51f9dae3025979125@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:

> I just accidentally founf that you can include a file just by using the name
> without the extension.  :)

AND, since I can't write any code the correct way THE FIRST TIME, I had somehow
converted all of the color_map indices to a NAN, but somehow POV-Ray rendered
the scene anyway!

I wonder if it took all of the color values and just spanned them across the
default 0 ... 1 span...  really weird, but really interesting.

(just change the max function for the remapping to min so that it's always 0 ...
0)


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