gradient bands

gradient bands

Post by Peter Cartwrig » Fri, 06 Sep 2002 08:02:13



The gradient produced in GIMP is perfect.  But when exported as a jpg
for example the bands appear as in other photoeditors. I there some
way of curing the problem?
 
 
 

gradient bands

Post by Dave Near » Fri, 06 Sep 2002 18:23:14


On 4 Sep 2002 16:02:13 -0700, Peter Cartwright said:

Quote:> The gradient produced in GIMP is perfect.  But when exported as a jpg
> for example the bands appear as in other photoeditors. I there some
> way of curing the problem?

You could try saving your jpeg with higher quality? Although jpeg
shjould save gradients pretty well, there being no edging effects
to worry about...

Are you sure you're not saving the gradients as .gif or some
other indexed type? Indexing a gradient is always hard because
(by it's nature) there are lots of colours in the gradient - often
more than the 255 limit for gifs. So you get a banding effect,
where a number of colours quite close together get merged into
one colour, and the gradient looks like a step function or
something.

Does this help?

Cheers,
Dave.
--
           David Neary,
     E-Mail: bolsh at gimp dot org
CV: http://www.redbrick.dcu.ie/~bolsh/CV/CV.html

 
 
 

gradient bands

Post by Orrin Edwar » Fri, 06 Sep 2002 22:47:27



> The gradient produced in GIMP is perfect.  But when exported as a jpg
> for example the bands appear as in other photoeditors. I there some
> way of curing the problem?

I'm also looking for a solution to this problem. Gradients produced in
The Gimp and in POVRay both show banding when viewed in XnView, my
'slide show' program.

Orrin - www.orrin.org/
Linux by SuSE... a world without Windows

 
 
 

gradient bands

Post by Orrin Edwar » Sat, 07 Sep 2002 08:33:40



> On 4 Sep 2002 16:02:13 -0700, Peter Cartwright said:
> > The gradient produced in GIMP is perfect.  But when exported as a jpg
> > for example the bands appear as in other photoeditors. I there some
> > way of curing the problem?

> You could try saving your jpeg with higher quality? Although jpeg
> shjould save gradients pretty well, there being no edging effects
> to worry about...

> Are you sure you're not saving the gradients as .gif or some
> other indexed type? Indexing a gradient is always hard because
> (by it's nature) there are lots of colours in the gradient - often
> more than the 255 limit for gifs. So you get a banding effect,
> where a number of colours quite close together get merged into
> one colour, and the gradient looks like a step function or
> something.

It's not how the file is saved, but the rendering of the file by the
other program. I took a jpg with a smooth gradient made with POVRay
and tested it in some other programs... all running on the same
x-server/KDE/Linux system.

The Gimp - Nice smooth gradient
Opera 6.03 - Nice smoth gradient
Netscape 4.76 - Banding
XnView 1.25 - Banding
ImageMagik - Banding

Orrin - www.orrin.org/
Linux by SuSE... a world without Windows

 
 
 

gradient bands

Post by Marc 'BlackJack' Rintsc » Sat, 07 Sep 2002 20:02:46



Quote:> It's not how the file is saved, but the rendering of the file by the
> other program. I took a jpg with a smooth gradient made with POVRay and
> tested it in some other programs... all running on the same
> x-server/KDE/Linux system.

> The Gimp - Nice smooth gradient
> Opera 6.03 - Nice smoth gradient
> Netscape 4.76 - Banding
> XnView 1.25 - Banding
> ImageMagik - Banding

That sounds quite strange. You aren't using an 8 or 16 bit graphic mode?

If your X is running in 24 or 32 bit graphic mode I would like to see such
a jpeg image.

Ciao,
        Marc 'BlackJack' Rintsch

 
 
 

gradient bands

Post by Peter Cartwrig » Sun, 08 Sep 2002 03:44:53



> I'm also looking for a solution to this problem. Gradients produced in
> The Gimp and in POVRay both show banding when viewed in XnView, my
> 'slide show' program.

> Orrin - www.orrin.org/
> Linux by SuSE... a world without Windows

I had a look through the GIMP User Manual and saw a gradient..with
bands. So I believe it's the program and not my computer.  If anyone
thinks they can change my mind in this, please post a link to a simple
gradient of several hundred pixels.

Peter

 
 
 

gradient bands

Post by Orrin Edwar » Sun, 08 Sep 2002 05:51:28




> > It's not how the file is saved, but the rendering of the file by the
> > other program. I took a jpg with a smooth gradient made with POVRay and
> > tested it in some other programs... all running on the same
> > x-server/KDE/Linux system.

> > The Gimp - Nice smooth gradient
> > Opera 6.03 - Nice smoth gradient
> > Netscape 4.76 - Banding
> > XnView 1.25 - Banding
> > ImageMagik - Banding

> That sounds quite strange. You aren't using an 8 or 16 bit graphic mode?

> If your X is running in 24 or 32 bit graphic mode I would like to see such
> a jpeg image.

> Ciao,
>    Marc 'BlackJack' Rintsch

The laptop that I use for slideshows is probably 16 bit graphic mode
since the X info page says something about 16 planes for the depth of
the window but it's LCD driver is limited to that. Yet even though it
is 16 bits, some software show a smooth gradient while others show
bands. Since my last message I have found that both Kongueror and
KView in the KDE package displays the gradient as smooth.

A sample image with a gradient is http://www.orrin.org/widls31.jpg

Orrin - www.orrin.org/
Linux by SuSE... a world without Windows

 
 
 

gradient bands

Post by Marc 'BlackJack' Rintsc » Mon, 09 Sep 2002 04:34:16



Quote:> The laptop that I use for slideshows is probably 16 bit graphic mode
> since the X info page says something about 16 planes for the depth of
> the window but it's LCD driver is limited to that. Yet even though it
> is 16 bits, some software show a smooth gradient while others show
> bands. Since my last message I have found that both Kongueror and
> KView in the KDE package displays the gradient as smooth.

> A sample image with a gradient is http://www.orrin.org/widls31.jpg

Looks okay here even in XnView. But I'm running X at 32 bits per pixel.
Maybe Gimp and KDE apps are dithering the image on 16 bit displays!?

Ciao,
        Marc 'BlackJack' Rintsch

 
 
 

gradient bands

Post by Marc 'BlackJack' Rintsc » Mon, 09 Sep 2002 04:34:18




Quote:> I had a look through the GIMP User Manual and saw a gradient..with
> bands. So I believe it's the program and not my computer.

Which program? And in what format was the GUM? Online or Paper?

Quote:> If anyone
> thinks they can change my mind in this, please post a link to a simple
> gradient of several hundred pixels.

http://www.spline.de/~bj/gradient.png

and

http://www.spline.de/~bj/gradient.jpg

Ciao,
        Marc 'BlackJack' Rintsch

 
 
 

gradient bands

Post by Peter Cartwrig » Mon, 09 Sep 2002 23:30:35



Quote:

> http://www.spline.de/~bj/gradient.png

> and

> http://www.spline.de/~bj/gradient.jpg

> Ciao,
>    Marc 'BlackJack' Rintsch


Quote:

> http://www.spline.de/~bj/gradient.png

> and

> http://www.spline.de/~bj/gradient.jpg

> Ciao,
>    Marc 'BlackJack' Rintsch

If you're seeing a smooth gradient and I'me not and I'me not.  It must
be my 16 bit monitor after all.  Still mystified though why  in that
case gradients are smooth before being exported.
 
 
 

gradient bands

Post by Orrin Edwar » Tue, 10 Sep 2002 04:31:18




> > http://www.spline.de/~bj/gradient.png

> > and

> > http://www.spline.de/~bj/gradient.jpg

> > Ciao,
> >       Marc 'BlackJack' Rintsch


> > http://www.spline.de/~bj/gradient.png

> > and

> > http://www.spline.de/~bj/gradient.jpg

> > Ciao,
> >       Marc 'BlackJack' Rintsch

> If you're seeing a smooth gradient and I'me not and I'me not.  It must
> be my 16 bit monitor after all.  Still mystified though why  in that
> case gradients are smooth before being exported.

With regard to the image at the URL above.... In Netscape I see
banding and in Opera and Konqueror I see a smooth gradient. From what
I can determine, The Gimp produces a smooth gradient but some other
software renders it poorly!

Orrin - www.orrin.org/
Linux by SuSE... a world without Windows

 
 
 

gradient bands

Post by Marc 'BlackJack' Rintsc » Tue, 10 Sep 2002 21:30:21




Quote:> If you're seeing a smooth gradient and I'me not and I'me not.  It must
> be my 16 bit monitor after all.  Still mystified though why  in that
> case gradients are smooth before being exported.

Both are smooth for me (24/32 bit). The "mystery" about gradients seem to
be smooth in some applications like Gimp and KDE apps even on 16 bit
displays is dithering. Here's a 4x zoom of a gradient in XnView and Gimp
on a 16 bit display:

http://www.spline.de/~bj/16bit_gradient.png

Ciao,
        Marc 'BlackJack' Rintsch

 
 
 

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In 16 bit (thousands) video mode, all gradients are going to look crappy -
make sure you work in 24/32 bit (millions) mode.

Did you turn on dithering for the gradient - that will reduce the banding
effect by adding a little bit of noise.

Chris


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