Hello,

Is there a standard method for 'upsampling' 8 bit greyscale images to 16 bit
using MacMegaPov?  I know that POV can read 8 bits and write 16 but without
an imtermediate smoothing step the resultant image isn't any smoother.  I
think what I need is a good old fasioned gaussian blur but am unsure how to
accomplish that within MacMegaPov.  Can anyone advise?

Thanks,

Glenn

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In article <B58C4F35.5F55%gle### [at] isrvcom> , Glenn Greenway 
<gle### [at] isrvcom>  wrote:

> Is there a standard method for 'upsampling' 8 bit greyscale images to 16 bit
> using MacMegaPov?  I know that POV can read 8 bits and write 16 but without
> an imtermediate smoothing step the resultant image isn't any smoother.

A computer screen can only display 8 bits per colour component, which also
limits it to 256 (8 bit) levels of grey.  You will not be able to see the
difference on screen if you use 65536 (16 bit) levels of grey.

16 bit per colour component or 16 bit greyscale for output are only useful
if you plan to post process the image in a program like PhotoShop, i.e. in
order to print it.


     Thorsten

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On Sat, 08 Jul 2000 14:23:06 +0200, Thorsten Froehlich wrote...
> > Is there a standard method for 'upsampling' 8 bit greyscale images to 16 bit
> > using MacMegaPov?  I know that POV can read 8 bits and write 16 but without
> > an imtermediate smoothing step the resultant image isn't any smoother.
> 
> A computer screen can only display 8 bits per colour component, which also
> limits it to 256 (8 bit) levels of grey.  You will not be able to see the
> difference on screen if you use 65536 (16 bit) levels of grey.
> 
> 16 bit per colour component or 16 bit greyscale for output are only useful
> if you plan to post process the image in a program like PhotoShop, i.e. in
> order to print it.

16bit grayscales could be useful for Heightfields, I suppose...

And I suppose that using interpolate 2 or 4 on an image mapped surface 
could get you some more colour depth, but usually it just blurs the 
detail in the image.

Bye for now,
     Jamie.

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> From: jam### [at] dh70qdu-netcom (Jamie Davison)
> Newsgroups: povray.general
> Date: Sat, 8 Jul 2000 15:35:19 +0100
> Subject: Re: Smoothing 8 bit greyscale images
> 
> On Sat, 08 Jul 2000 14:23:06 +0200, Thorsten Froehlich wrote...
>>> Is there a standard method for 'upsampling' 8 bit greyscale images to 16 bit
>>> using MacMegaPov?  I know that POV can read 8 bits and write 16 but without
>>> an imtermediate smoothing step the resultant image isn't any smoother.
>> 
>> A computer screen can only display 8 bits per colour component, which also
>> limits it to 256 (8 bit) levels of grey.  You will not be able to see the
>> difference on screen if you use 65536 (16 bit) levels of grey.
>> 
>> 16 bit per colour component or 16 bit greyscale for output are only useful
>> if you plan to post process the image in a program like PhotoShop, i.e. in
>> order to print it.
> 
> 16bit grayscales could be useful for Heightfields, I suppose...
> 
> And I suppose that using interpolate 2 or 4 on an image mapped surface
> could get you some more colour depth, but usually it just blurs the
> detail in the image.
> 
> Bye for now,
> Jamie.
>

Hello again,

Thanks for the useful information.  However, perhaps my initial post wasn't
very clear.  I'm particularly interesed in image maps being used to modulate
isosurfaces.  So far my attempts have been pretty rough looking. I'm
assuming the roughness is a result of using 8 bit grey scale images.  The
Pov documentaion is pretty specific about the inherent value of 16 bit grey
scale with regard to heightfields.  It seems to me that if a user could
'upsample' and blur the 8 bit images, the resultant 16 bit would be a lot
smoother when applied to an isosurface.  I can't believe the power and
elegance of the isosurface patch.  Even a simple gradient image when applied
spherically of cylindrically to an appropriate isosurface results in
fabulous deformation.  If I can just 'smooth' those images....

Thanks a zillion,

Glenn

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On Sat, 08 Jul 2000 13:00:03 -0400, Glenn Greenway wrote...
[snip]
> Thanks for the useful information.  However, perhaps my initial post wasn't
> very clear.  I'm particularly interesed in image maps being used to modulate
> isosurfaces.  So far my attempts have been pretty rough looking. I'm
> assuming the roughness is a result of using 8 bit grey scale images.  The
> Pov documentaion is pretty specific about the inherent value of 16 bit grey
> scale with regard to heightfields.  It seems to me that if a user could
> 'upsample' and blur the 8 bit images, the resultant 16 bit would be a lot
> smoother when applied to an isosurface.  I can't believe the power and
> elegance of the isosurface patch.  Even a simple gradient image when applied
> spherically of cylindrically to an appropriate isosurface results in
> fabulous deformation.  If I can just 'smooth' those images....

Oops, he mentioned the 'I' word...

Sorry, I play with POV primarily through Moray, so I haven't needed to 
wrap my brain around isosurfaces yet.

As far as smoothing greyscale bitmaps goes, do you have access to 
Photoshop or Paint Shop Pro, or the GIMP?  Any of those should be able to 
apply a gaussian blur to the images and save the resulting image out with 
a greater bit depth.

Bye for now,
     Jamie.

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Glenn Greenway wrote:
> very clear.  I'm particularly interesed in image maps being used to modulate
> isosurfaces.  So far my attempts have been pretty rough looking. I'm
> assuming the roughness is a result of using 8 bit grey scale images.  The
...
> fabulous deformation.  If I can just 'smooth' those images....

In fact, using "interpolate" 2 or 4 into your image_map statement will
do what your are seeking for, and even better, since instead of 65000
levels, you will get virtually infinite levels.

Fabien.

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Thorsten Froehlich wrote:
> 
> ...
> A computer screen can only display 8 bits per colour component, which also
> limits it to 256 (8 bit) levels of grey.  You will not be able to see the
> difference on screen if you use 65536 (16 bit) levels of grey.
> 
> 16 bit per colour component or 16 bit greyscale for output are only useful
> if you plan to post process the image in a program like PhotoShop, i.e. in
> order to print it.


Hmmm... Hmmmm... Hmmmmm....

Are you really sure about this ?

I thought that most of today's monitors can show as 
many different levels of grey (monochrome) as the 
graphics adapter (video card) can produce. 
This is because they are analogue.

(There are of coarse limitations. Because the 
bandwidth of the monitor's electronic, phosphor and 
optical parts is limited. Another limiting factor
is presence of noise; both electrical and "optical".)

And yes; if the D/A-converter(s) on the video card
are only 8 bit (RGB: 3*8bit = 24bit), then max 256
different monochrome levels can be produced by it.

But if one for instance has a video card with 3 
D/A-converters, each with 12-bits, then it could 
produce 4096 levels of grey.


Tor Olav
--
mailto:tor### [at] hotmailcom
http://www.crosswinds.net/~tok/tokrays.html

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Thanks again for your input,

However, I've tried Photoshop and interpolate options to no avail.  Perhaps
I'm missing something substantial but even my height fields look banded, as
do my isosurfaces.  What I really want to do is sketch out my image map in
Photoshop then use it do displace isosurfaces or height fields:
unfortunately the rendered images show considerable banding.


Any other thoughts,

Glenn

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Jamie Davison wrote:

> As far as smoothing greyscale bitmaps goes, do you have access to
> Photoshop or Paint Shop Pro, or the GIMP?  Any of those should be able to
> apply a gaussian blur to the images and save the resulting image out with
> a greater bit depth.

Be forewarned: I don't think the standard current version of the GIMP
supports 16-bit greyscale.  There is a 16-bit version of the GIMP (i.e.
16 bits for each of red, green, blue, alpha) being developed for the
film industry (with some subsidy), since they're the ones chiefly
interested in that sort of color depth at this point.  Eventually that
functionality will be merged back into the main branch of GIMP
development.  The 16-bit version is referred to as Hollywood GIMP.  It's
home page is http://film.gimp.org/index.html.  I haven't had a chance to
play with it yet, but I did some looking into this at a time when I
wanted a 16-bit heightfield.

-Mark Gordon

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"Glenn Greenway" <gle### [at] isrvcom> wrote in message
news:B58D18EA.5F71%gle### [at] isrvcom...
|
|  What I really want to do is sketch out my image map in
| Photoshop then use it do displace isosurfaces or height fields:
| unfortunately the rendered images show considerable banding.
|
| Any other thoughts,

There just aren't any 16-bit image "editing" programs far as I know, except
for Mark Gordon mentioning the Hollywood Gimp which is (good) news to me.
Fractint can output 16 bit fractal images, but no control over them like a
hand-drawn picture.
There's a chance you could use your 8-bit image in a image_map pigment on a
plane and then focal blur it with very fine settings.  Sorry if that's been
said already.  Then just output using 'hf_grey_16 on' in the
'global_settings'.  Obviously not a perfect solution.

Bob

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