Just to get it on record:  Specifying --no-interpolate-imagery as a "global" 
switch fixed the issue.

-B



-----Original Message-----
From: [email protected] 
[mailto:[email protected]] On Behalf Of Brad Colbert
Sent: Thursday, September 26, 2013 12:39 PM
To: OpenSceneGraph Users
Subject: Re: [osg-users] VPB adding noise to imagery

Hi folks,

I tried --RGB-16 and I get the same effect.  There is some kind of sampling 
going on and it's hard to tell what it is.  The same pattern is in all color 
channels.

Any ideas?

-B



From: [email protected] 
[mailto:[email protected]] On Behalf Of Arthur Bogard
Sent: Thursday, September 26, 2013 12:11 PM
To: OpenSceneGraph Users
Subject: Re: [osg-users] VPB adding noise to imagery

I've found that RGB-16 solves my issues, but not RGBA

On Thu, Sep 26, 2013 at 6:39 PM, Brad Colbert <[email protected]> wrote:
Hi Robert,

Maybe I'm using the wrong switch?  From my email below "the target has 
compression disabled using -RGBA."

Does this need to be specified after each -layer # switch?

-B



From: [email protected] 
[mailto:[email protected]] On Behalf Of Robert Osfield
Sent: Thursday, September 26, 2013 11:27 AM
To: OpenSceneGraph Users
Subject: Re: [osg-users] VPB adding noise to imagery

HI Brad,

My guess is that it's an artefact of using OpenGL/ST3C compression that the OSG 
uses by default to keep the tile sizes.  You can disable compression when doing 
the VPB build by choosing an RGB output format.  Run osgdem --help to see all 
the options.

Robert.

On 26 September 2013 17:39, Brad Colbert <[email protected]> wrote:
Hi folks,
 
We are building a database using an additional texture layer as a height field. 
 I'm finding that the image stored in database is coming across with what 
appears to be 1bit noise.  A constant image of say, 125 / 255 after going 
through VPB is coming out with some values of 124 / 255.  The pattern looks a 
bit like quantization noise but we are setting --disable-error-diffusion just 
in case and the target has compression disabled using -RGBA.
 
Does anyone in OSG land have an idea where I can look to see what is causing 
this?
 
I'm attaching captured images where I've applied the same stretching formula.  
One is from the rendering of the database and the other is from Mathcad, where 
I loaded the source image and displayed it with the same stretch.  The database 
image capture shows the "speckles" where as the source image does not.
 

 

 
 
-B
 
---
Brad Colbert
Renaissance Sciences Corporation
(480) 290-3997
 

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