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Glen,
Attached you will find a small jpg image_map (ugly.jpg) and a
rendered image (GBerry.jpg) illustrating the undersirable conseq-
uenses of using .jpg images as an input format. Had the original
image not been compressed in the .jpg format the artifacts you
see in the final result would never have appeared. In this case
I forced the quality to be lower in the jpg before converting to
.tga just to prove my point but it illustrates it well.
It is not at all unusual to find "texture" sites on the web with
extremly poor quality jpg's but some of them are just attactive
enough that you might attemt to use them anyway. In those cases
I am forced to try to clean them up before converting them to a
format usable by POV-Ray. If POV-Ray were to accept jpgs as input
for image_maps I would still try to clean them up but would still
run the risk of losing quality when I resave them in .jpg format
because the damage done by the jpg compression algorithm is prog-
ressive.
In my opinion the .jpg image format sucks. PNG is a much better
option and POV-Ray already supports it.
--
Ken Tyler - 1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/
Post a reply to this message
Attachments:
Download 'ugly.jpg' (3 KB)
Download 'gberry.jpg' (11 KB)
Preview of image 'ugly.jpg'
Preview of image 'gberry.jpg'
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On Mon, 21 Feb 2000 10:25:27 -0800, Ken <tyl### [at] pacbell net> wrote:
>
>Glen,
>
> Attached you will find a small jpg image_map (ugly.jpg) and a
>rendered image (GBerry.jpg) illustrating the undersirable conseq-
>uenses of using .jpg images as an input format.
Well, those certainly are bad. However, they are also not typical
examples of a sane JPEG input image. Everyone should know that the
simple image you presented would be better represented in the PNG
format. When I talk about using JPEG for input, I mean fo use it for
those types of images it works best on, particularly on typical
continous-tone photographic images - and no, a photograph of four,
colored, textureless squares wouldn't count. :)
I also intend to use JPEG images that have been compressed using
appropriate quality settings. Compressing the image too much would
make it unsuitable as well.
It's a trivial matter to come up with images that look miserable with
JPEG compression, especially *poor* JPEG compression. However, that
shouldn't preclude the use of other images that *are* suited to JPEG
compression, and have been compressed with appropriage settings.
> It is not at all unusual to find "texture" sites on the web with
>extremly poor quality jpg's but some of them are just attactive
>enough that you might attemt to use them anyway.
Well you shouldn't use poor quality images for input. If you do, it's
your own fault. However, not all JPEG images are of poor quality.
I could also find you some horrible looking PNG, BMP, GIF, and TARGA
images if I wanted to. Would that be reason enough to ban those
formats as well?
Later,
Glen Berry
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Ken wrote:
> In my opinion the .jpg image format sucks. PNG is a much better
> option and POV-Ray already supports it.
My 2 cents : when storage space or file management is an issue, large images
can be converted to JPG with a good compression with little or at least
acceptable loss in quality. The Sony Cybershot digital camera uses it to store
its files on its memory stick and IMHO the result is perfect (we've been using
these files for professional documention). Another example below : the picture
is a detail from a 22 Mb rendering. The left image is from the original
(stored as a 7 Mb PNG). The image on the right is from a jpg compressed with a
1/11 ratio (stored as a 953 kb Jpg). The present combo is a jpg obtained with
the minimum compression available.
You can see the difference if you magnify the jpg image, and even without
magnifying there are visible artifacts (lines belows the lampshade). However,
both the (original) images would be perfectly suitable for printing. And while
the 953 kb JPG file can be sent by email (after taking the proper
precautions), the 7 Mb PNG usually can't... I had to do this some time ago
and, though this was very surprising at first, it made me realize that JPG,
when handled wisely, can save the day.
The day POV supports JPG input, I'll quicky convert the larger image maps
(with the proper compression ratio !!!), because it will make managing the
projects easier (like saving them on CD-ROMs, or transferring them between
machines). I can already do that, but it requires zipping or converting the
files back and forth, which is not very practical (and saving in PNG takes a
while, particularly with large files). However I'll keep storing as PNGs the
final renderings, the small image maps, the few image maps that behave too
strangely in JPG and those with an alpha channel. And yes, I'll still miss
(just a little) a jpeg saving feature in pov, because I think that it would
have been very handy during the test renders (and the possibility of launching
by mistake a week-long final render in JPG format is not worse than any other
mistake I can do at this always febrile and exciting moment).
G.
Post a reply to this message
Attachments:
Download 'chcpare.jpg' (88 KB)
Preview of image 'chcpare.jpg'
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On Mon, 21 Feb 2000 21:18:23 +0100, Gilles Tran <tra### [at] inapginrafr>
wrote:
>Ken wrote:
>
>> In my opinion the .jpg image format sucks. PNG is a much better
>> option and POV-Ray already supports it.
>
>My 2 cents : when storage space or file management is an issue, large images
>can be converted to JPG with a good compression with little or at least
>acceptable loss in quality.
Thank you Gilles, for showing everyone a worthwhile use of JPEG.
Later,
Glen Berry
Post a reply to this message
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The three best options to compress images are PNG, GIF, and JPEG, depending
upon what the image is. These crappy squares would obviously work best in PNG
or GIF, although they still would be pretty small with a decent JPEG
compressor. Big fancy renders, for internet purposes, are better off in JPEG
because loss is minimal and there are so many colors. When I made the Escher
gallery, I had to get all the images in JPEG and convert them to PNG so POV
could read them, and that was a waste of time and disk space (the PNGs are
*much* bigger, unfortunately, converting it doesn't get rid of the loss).
There are no horrid artifacts for you to complain about.
The whole idea of using JPEG in the first place was for this exact purpose;
getting pictures of the 'net without converting them. It's up to the person
who posts it on the net in the first place to pick an appropriate format. I
don't think anyone around here wants to wait for a 5M PNG when they can get a
90k JPEG with slight noticeable loss or even a 600k JPEG that's almost exactly
the same.
--
___ ______________________________________________________
| \ |_ <dav### [at] faricynet> <ICQ 55354965>
|_/avid |ontaine http://www.faricy.net/~davidf/
"Sitting on a cornflake, waiting for the van to come" -Beatles
Post a reply to this message
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Gilles Tran wrote:
>Ken wrote:
>
>> In my opinion the .jpg image format sucks. PNG is a much better
>> option and POV-Ray already supports it.
>
>My 2 cents :
What a pitty you didn't post it as a PNG, now we are comparing 1x JPEG
compression and 2x JPEG compression.
In the right picture, without zooming I see a loss of detail in the hair,
its more fuzzy. Around the lampost there seems to be an extra contour and
the edge of it if softer. Under the lamp in the orange on the wall the
horizontal lines are more prominent There seems to be more structure in the
yellow on the wall. The colour fade on the womans back, from the spline to
the side is less smooth.
There is a JPEG compression utility at:
http://vision.arc.nasa.gov/dctune/dctune2.0.html
It has a somewhat different approach, you can specify the visual quality
instead of the compression rate. Or you can set the desired file size.
O T: A link for you Gilles, http://www.atelier-fresson.com/
It seems they have opend up their buissenis a bit more, there is even an
price list (and the prices are stunning).
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
Post a reply to this message
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Glen Berry wrote:
>
> On Mon, 21 Feb 2000 10:25:27 -0800, Ken <tyl### [at] pacbellnet> wrote:
>
> >
> >Glen,
> >
> > Attached you will find a small jpg image_map (ugly.jpg) and a
> >rendered image (GBerry.jpg) illustrating the undersirable conseq-
> >uenses of using .jpg images as an input format.
>
> Well, those certainly are bad. However, they are also not typical
> examples of a sane JPEG input image.
You asked for an example and I provided what I felt is the best possible
example to illustrate my point. Now you criticize me for finding one that
excels at what I wanted to illustrate. Shame on you :)
--
Ken Tyler - 1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/
Post a reply to this message
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>The colour fade on the womans back, from the spline to
>the side is less smooth.
Can you believe I thought it was a mountain with a cave and grass at the
top? I had to double check when I read your post.
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"TonyB" <ben### [at] panamac-comnet> wrote :
>
> Can you believe I thought it was a mountain with a cave and grass at the
> top? I had to double check when I read your post.
>
That's what I thought too...! I was trying to figure out why the UFO was
beaming up kelp from the valley.
Post a reply to this message
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Bill DeWitt wrote:
>
>"TonyB" <ben### [at] panamac-comnet> wrote :
>>
>> Can you believe I thought it was a mountain with a cave and grass at
>> the top? I had to double check when I read your post.
>>
>
> That's what I thought too...! I was trying to figure out why the UFO
> was
>beaming up kelp from the valley.
>
>
Bad, bad compression ...
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
Post a reply to this message
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