POV-Ray : Newsgroups : povray.general : image_map & interpolate ? Server Time
6 Dec 2021 12:05:01 EST (-0500)
  image_map & interpolate ? (Message 1 to 3 of 3)  
From: tth
Subject: image_map & interpolate ?
Date: 21 Nov 2021 07:50:49
Message: <619a40a9$1@news.povray.org>
Hello.

I'm looking at interpolate in the wiki, and I've not found the
option for "no interpolate", is there a reason for that ?

https://wiki.povray.org/content/Reference:Bitmap_Modifiers

I'm trying to map a low-res picture as pixel-art.


tTh

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From: William F Pokorny
Subject: Re: image_map & interpolate ?
Date: 21 Nov 2021 09:07:11
Message: <619a528f$1@news.povray.org>
On 11/21/21 7:50 AM, tth wrote:
> 
> Hello.
> 
> I'm looking at interpolate in the wiki, and I've not found the
> option for "no interpolate", is there a reason for that ?
> 
> https://wiki.povray.org/content/Reference:Bitmap_Modifiers
> 
> I'm trying to map a low-res picture as pixel-art.
> 
> 
> tTh
> 

Hi.

IIRC, With official POV-Ray versions, to get no interpolation - with 
image maps - the only way is to not use the interpolate keyword. The 
parser doesn't allow 'interpolate 0' with image maps though this is the 
no interpolation value internally.

POV-Ray is set up inconsistently with respect to the interpolate 
keyword. It sometimes supports a '0' no interpolation mode (ie density 
files) and other places not. The differences in specification method are 
for no reasons I can see(1).

Bill P.

(1) - My playpen povr branch supports 'interpolate 0' for no 
interpolation everywhere.

Aside: There is often good reason to turn off interpolation. Performance 
in development renders and where the image maps are already larger than 
the as rendered resolution being others. In not always supporting a no 
interpolation mode 'value', POV-Ray makes switching between no 
interpolation and interpolation awkward.


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From: Kenneth
Subject: Re: image_map & interpolate ?
Date: 21 Nov 2021 16:55:00
Message: <web.619abf41a3e847a14cef624e6e066e29@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

>
> IIRC, With official POV-Ray versions, to get no interpolation - with
> image maps - the only way is to not use the interpolate keyword. The
> parser doesn't allow 'interpolate 0' with image maps though this is the
> no interpolation value internally.
>

Correct.

I sometimes use POV-ray to re-render animation frames and/or frames extracted
from a video as exact 1:1 pixel reproductions. In such cases, I leave
interpolate OFF-- although, from many tests I've made, it has absolutely no
effect, and can be on or off. Not so with antialiasing though. Depending on the
particular AA settings, there is a very subtle difference in the 1:1
reproduction. At 'higher quality' AA values (and using an exaggerated
'difference' test in an image-editing app to see what occurs) the difference
shows up as what looks like random 'pixel stars.' It's subtle but it's there. So
I turn AA off as well.

For the OP's pixel art idea, I would assume that he is zooming-in on the
image_map to see the individual pixels. Regarding AA, I don't know if it should
be used or not, as I've never tested that particular set-up. I guess it would
improve the *overall* render, if there happen to be actual objects in the scene
as well.


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