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> I wouldn't believe it but I see the banding in my reder (3.6.1)
> as well. A color analysis via gimp showed that the color
> of neighbouring bands differ by just one value step (8 bit: 1 step
> 1/255). This means that a smooth gray gradient with closed one color
> fields cannot be achieved with 24bit colours.
More precisely, it can't be achieved with 24-bit RGB. There are colour
bases in which 24-bit precision is easily enough to get a smooth
gradient.
--
There may come a time The open palm of desire,
When I will lose you, ]http://surreal.istic.org/[ The rose of Jericho,
Lose you as I lose my sight, Soil as soft as Summer,
Days falling backward into velvet night; The strength to let you go.
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> More precisely, it can't be achieved with 24-bit RGB. There are colour
> bases in which 24-bit precision is easily enough to get a smooth
> gradient.
Even more precisely, a smooth *grey* gradient. Sorry for the inaccuracy.
I noticed it as soon as I pressed send. :-(
--
There may come a time The open palm of desire,
When I will lose you, ]http://surreal.istic.org/[ The rose of Jericho,
Lose you as I lose my sight, Soil as soft as Summer,
Days falling backward into velvet night; The strength to let you go.
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Hall nous apporta ses lumieres en ce 2005-07-31 11:26:
> using pov-ray 3.6.1 for windows on windows XP...
> Should I be seeing the banding produced in this minimal scene file?
> (Is this a limitation of POV's precision, or a bug? banding is stronger in
> original bmp of picture)
>
> camera { location <-4,4,-4> look_at <0,0,0> right <1,0,0> up <0,1,0> }
> light_source { <1,1,-1> color rgb 1 }
> plane { <0,1,0>, 0 pigment{color rgb 1} }
>
> and result....
>
>
>
>
I don't see any banding, display set at 32 (24) BBP.
Switching to 16 BBP and I dee very distinct and distracting banding. Back to 32 BBP!
Alain
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Are you sure this isn't a what-his-name optical illusion? A mach band. The
one where the mind adds color banding. Have you taken the low bit image
into a manipulation program and run the eyedropper over it, to make sure
the bands are real?
-s
5TF!
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"Hall" <tre### [at] ww-interlink net> wrote in message
news:42eceda8@news.povray.org...
> using pov-ray 3.6.1 for windows on windows XP...
> Should I be seeing the banding produced in this minimal scene file?
> (Is this a limitation of POV's precision, or a bug? banding is stronger in
> original bmp of picture)
>
> camera { location <-4,4,-4> look_at <0,0,0> right <1,0,0> up <0,1,0> }
> light_source { <1,1,-1> color rgb 1 }
> plane { <0,1,0>, 0 pigment{color rgb 1} }
>
> and result....
Are you running an ICC profile on your monitor?
If you are seeing *colour* bands (such as slightly red, green, or blue hues when
compared with neighbouring bands) in this greyscale image (even after you
desaturate it, or convert it to a pure greyscale image, in a paint program), it
could be because you're running an ICC profile for your monitor and, in the
process of changing the output signal to make it match a specific response
curve/black point/colour temperature, is introducing slight variations in the
output hue. Thus a specific output level like RGB 128, 128, 128, could become
129, 128, 128, causing one band to appear slightly red, while the one next to it
at RGB 127, 127, 127 could be changed to 127, 128, 127, making it appear
slightly blue. This can also introduce (if the profile isn't accurate) larger
than normal steps in the lightness of bands.
Check your colour management to see if a profile is enabled - if it is, try
disabling it, restarting, and checking if the bands are gone (or aren't as
significant).
Lance.
thezone - thezone.firewave.com.au
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"Lance Birch" <-> wrote in message news:42eda11f$1@news.povray.org...
<snip>
> at RGB 127, 127, 127 could be changed to 127, 128, 127, making it appear
> slightly blue.
Err... green. :)
Lance.
thezone - thezone.firewave.com.au
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Hall wrote:
> using pov-ray 3.6.1 for windows on windows XP...
> Should I be seeing the banding produced in this minimal scene file?
> (Is this a limitation of POV's precision, or a bug? banding is
> stronger in original bmp of picture)
>
> camera { location <-4,4,-4> look_at <0,0,0> right <1,0,0> up <0,1,0> }
> light_source { <1,1,-1> color rgb 1 }
> plane { <0,1,0>, 0 pigment{color rgb 1} }
>
> and result....
What monitor do you have? Some old/cheap LCDs only do interpolated 18-bit
colour rather than true 24-bit. If it's quoted as being able to display
16.2 million colours, it's 18-bit, true 24-bit is 16.7 million colours. On
this pattern the interpolation your monitor is doing might be more visible.
Have you tried doing a gradient in another program, like powerpoint?
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Hall wrote:
> using pov-ray 3.6.1 for windows on windows XP...
> Should I be seeing the banding produced in this minimal scene file?
> (Is this a limitation of POV's precision, or a bug? banding is stronger in
> original bmp of picture)
Fredrick's got it right. The banding is natural for this kind of image
at 24-bit precision, as you effectively only have 8 bits of pure gray to
work with.
Outputting at 48 bits and then dithering down in another app (probably
GIMP or Photoshop) should help reduce the banding; it will also make
your image a bit grainy, but it shouldn't be visibly so. Alternately,
introducing more noise or color to the scene, or adding noise in
post-processing, should eliminate the banding.
-Xplo
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"scott" <sco### [at] spamcom> wrote in message news:42edd2f4@news.povray.org...
> Hall wrote:
> > using pov-ray 3.6.1 for windows on windows XP...
> > Should I be seeing the banding produced in this minimal scene file?
> > (Is this a limitation of POV's precision, or a bug? banding is
> > stronger in original bmp of picture)
> >
> > camera { location <-4,4,-4> look_at <0,0,0> right <1,0,0> up <0,1,0> }
> > light_source { <1,1,-1> color rgb 1 }
> > plane { <0,1,0>, 0 pigment{color rgb 1} }
> >
> > and result....
>
> What monitor do you have? Some old/cheap LCDs only do interpolated 18-bit
> colour rather than true 24-bit. If it's quoted as being able to display
> 16.2 million colours, it's 18-bit, true 24-bit is 16.7 million colours.
On
> this pattern the interpolation your monitor is doing might be more
visible.
> Have you tried doing a gradient in another program, like powerpoint?
>
>
I see this banding on the two computers we have---both are using crt
monitors and are running in 32 bit (true color mode)....
In PSP when doing a pure gray gradient, the banding is also visible....but
when doing pure red or blue or green, the banding is not visible.
I agree, as was said by some others, this is a limitation of the 24 bit
nature of true color displays...will stick to using more color in pictures
from now on...if I ever get a system capable of 48 bit color display, then I
will try working with pure greyscale pictures again.
hexhall
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> I see this banding on the two computers we have---both are using crt
> monitors and are running in 32 bit (true color mode)....
> In PSP when doing a pure gray gradient, the banding is also
> visible....but when doing pure red or blue or green, the banding is
> not visible.
> I agree, as was said by some others, this is a limitation of the 24
> bit nature of true color displays...will stick to using more color in
> pictures from now on...if I ever get a system capable of 48 bit color
> display, then I will try working with pure greyscale pictures again.
You could turn the contrast down on your monitor :-)
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