I'm producing a CD based website for someone who has given me a number of
bmp files generated by POV-Ray 3.1 for windows. The website has to be
viewable in a minimum of 16 bit high color, at 800 x 600 resolution and be
viewable in internet explorer 3.0 from microsoft. Naturally image quality is
important but it is also important to deliver the images effectively via a
web browser interface.

The problem I have is that in order to view the images in internet explorer
3.0 (which does not support bmp or png file formats) i'm converting the
original bmp files to the jpg file format. With a low compression ratio the
loss in image quality is acceptable. However when i drop my machine's color
depth down from 32 bit true color to the required minimum of 16 bit high
color I get color banding or concentric circles on the images.

I've tried using various image manipulation techniques to reduce the color
depth without effecting the image quality too seriously, but nothing seems
to get rid of the color banding or concentric circles without completely
destroying the pictures. I've also had a play with POV-Ray (since i've been
given the original files too) but nothing i've tried (including changing the
render settings and ini files) seems to work.

I have access to a large collection of image manipulation software such as
photoshop, paintshop pro etc, but nothing there seems to work either.

Please help, it's driving me nuts!

Thanks
Paul

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The easiest thing to do is to switch to 16-bit mode, view the image in
an image viewing program capable of dithering to 16-bit (such as
ACDSee or IrfanView or others) and taking a snapshot of the dithered
image.


Peter Popov
pet### [at] usanet
ICQ: 15002700

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In article <38b01ab1@news.povray.org> , "Paul" <ran### [at] freenetcouk> 
wrote:

> I'm producing a CD based website for someone who has given me a number of
> bmp files generated by POV-Ray 3.1 for windows. The website has to be
> viewable in a minimum of 16 bit high color, at 800 x 600 resolution and be
> viewable in internet explorer 3.0 from microsoft. Naturally image quality is
> important but it is also important to deliver the images effectively via a
> web browser interface.
>
> The problem I have is that in order to view the images in internet explorer
> 3.0 (which does not support bmp or png file formats) i'm converting the
> original bmp files to the jpg file format. With a low compression ratio the
> loss in image quality is acceptable. However when i drop my machine's color
> depth down from 32 bit true color to the required minimum of 16 bit high
> color I get color banding or concentric circles on the images.

I would suggest a requirement change from 16 bit to 24 bit color.
Browsers are not designed to be high-quality image viewers and the only
reasonable quality for an image will be available with 24 bit color. After
all a browser is not a WYSIWYG tool.
To view images on systems with less than 24 bit color, I would suggest an
image archive program, not a web browser.  However, more recent browser
versions should support dithering.


     Thorsten

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In article <=B2wONypFmTSczwg0nfX=2Y8XPNX@4ax.com> , Peter Popov 
<pet### [at] usanet>  wrote:

> The easiest thing to do is to switch to 16-bit mode, view the image in
> an image viewing program capable of dithering to 16-bit (such as
> ACDSee or IrfanView or others) and taking a snapshot of the dithered
> image.

Hmm, where is the point of this idea?  Most image programs can export as 16
bit, which isn't the problem here.  And t won't help for JPEG compression as
it will "damage" the dithering anyway.


       Thorsten

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On Sun, 20 Feb 2000 11:55:33 -0600, "Thorsten Froehlich"
<tho### [at] trfde> wrote:

>In article <=B2wONypFmTSczwg0nfX=2Y8XPNX@4ax.com> , Peter Popov 
><pet### [at] usanet>  wrote:
>
>> The easiest thing to do is to switch to 16-bit mode, view the image in
>> an image viewing program capable of dithering to 16-bit (such as
>> ACDSee or IrfanView or others) and taking a snapshot of the dithered
>> image.
>
>Hmm, where is the point of this idea?  Most image programs can export as 16
>bit, which isn't the problem here.  And t won't help for JPEG compression as
>it will "damage" the dithering anyway.
>
>
>       Thorsten

There's a point, believe me. Until two months ago I had a 2 MB video
board and so it could only go up to 16 bit color in 1024x768. I had
severe problems with my POV Desktop image. Windows does not dither the
wallpaper when in high-color mode so I had to apply this technique.
The image was made in PhotoShop and I don't recall any option for
saving it in 16 bit color from PS. Without the help of ACDSee, it
looked like a biodegradeable pile of animal waste material.


Peter Popov
pet### [at] usanet
ICQ: 15002700

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In article <5VawOGZIyBblIh58DebZ9fByVGFx@4ax.com> , Peter Popov 
<pet### [at] usanet>  wrote:

> There's a point, believe me. Until two months ago I had a 2 MB video
> board and so it could only go up to 16 bit color in 1024x768. I had
> severe problems with my POV Desktop image. Windows does not dither the
> wallpaper when in high-color mode so I had to apply this technique.
> The image was made in PhotoShop and I don't recall any option for
> saving it in 16 bit color from PS. Without the help of ACDSee, it
> looked like a biodegradeable pile of animal waste material.

Well, I am not talking about Photoshop here (and I think ImageReady which
comes with 5.5 has such an option) :-)  There are a lot of free image file
converters out there that will do a perfect job this way.


     Thorsten

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Paul wrote:
> 
> I'm producing a CD based website for someone who has given me a number of
> bmp files generated by POV-Ray 3.1 for windows. The website has to be
> viewable in a minimum of 16 bit high color, at 800 x 600 resolution and be
> viewable in internet explorer 3.0 from microsoft. Naturally image quality is
> important but it is also important to deliver the images effectively via a
> web browser interface.
> 
> The problem I have is that in order to view the images in internet explorer
> 3.0 (which does not support bmp or png file formats) i'm converting the
> original bmp files to the jpg file format. With a low compression ratio the
> loss in image quality is acceptable. However when i drop my machine's color
> depth down from 32 bit true color to the required minimum of 16 bit high
> color I get color banding or concentric circles on the images.
> 
> I've tried using various image manipulation techniques to reduce the color
> depth without effecting the image quality too seriously, but nothing seems
> to get rid of the color banding or concentric circles without completely
> destroying the pictures. I've also had a play with POV-Ray (since i've been
> given the original files too) but nothing i've tried (including changing the
> render settings and ini files) seems to work.
> 
> I have access to a large collection of image manipulation software such as
> photoshop, paintshop pro etc, but nothing there seems to work either.
> 
> Please help, it's driving me nuts!
> 
> Thanks
> Paul

Why concert to jpg. jpg is only good for 24bit colors. The compression
method will thrash any lower bit depth. Why do you not use "gif" or
"tif" they also compress the image, but they have special 16bit and eveb
8bit modes. So if you convert the images you could directly concert to a
16bit format (with dithering if wished). Photoshop could write such
formats if I'm not mistaken. Or let Pov render to those formats.

Axel

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