Question about a certain type of image defect

Every now and then on the web, I'll see photos which contain a large area of
color that was supposed to change smoothly from, say, dark red to light red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number things,
where you're supposed to change from one paint color to another. What causes
this? I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure it never
happens to my pictures.

"Doug Kanter" writes:
Every now and then on the web, I'll see photos which contain a large
area of color that was supposed to change smoothly from, say, dark
red to light red, based on the angle of the lighting. Instead, it
appears to change in zones or chunks, almost like the outlines you
see on those paint-by-number things, where you're supposed to change
from one paint color to another. What causes this?

It is called posterization, and it is usually caused by using a too
small colour palette. An unskilled operator may do this in any format
- but the most common cause is using the GIF-format for photographs.
The GIF-format has a maximum colour palette of only 256 colours -
which is fine for line art, but way too small for colour photographs.

I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure
it never happens to my pictures.

Learn to use your tools, and stay clear of the GIF-format for photos,
and you'll avoid posterization.

However, if you use the JPEG-format istead of GIF - there is another
defect you should be aware of: JPEG artifacts. This appear as "halos"
of discolouration around areas of high contrast. Doing repeated saves
of edited JPEG images, or using a too aggresive value for JPEG
compression is the cause of this problem.

To avoid format-induced defects, capture in camera RAW and do all your
post-processing using a non-lossy image format. (E.g.: PNG, TIFF or
PSD).
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
================================================== ======================
When you say you live in the real world, which one are you referring to?

"Doug Kanter" writes:
Every now and then on the web, I'll see photos which contain a large
area of color that was supposed to change smoothly from, say, dark
red to light red, based on the angle of the lighting. Instead, it
appears to change in zones or chunks, almost like the outlines you
see on those paint-by-number things, where you're supposed to change
from one paint color to another. What causes this?

It is called posterization, and it is usually caused by using a too
small colour palette. An unskilled operator may do this in any format
- but the most common cause is using the GIF-format for photographs.
The GIF-format has a maximum colour palette of only 256 colours -
which is fine for line art, but way too small for colour photographs.

I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure
it never happens to my pictures.

Learn to use your tools, and stay clear of the GIF-format for photos,
and you'll avoid posterization.

However, if you use the JPEG-format istead of GIF - there is another
defect you should be aware of: JPEG artifacts. This appear as "halos"
of discolouration around areas of high contrast. Doing repeated saves
of edited JPEG images, or using a too aggresive value for JPEG
compression is the cause of this problem.

To avoid format-induced defects, capture in camera RAW and do all your
post-processing using a non-lossy image format. (E.g.: PNG, TIFF or
PSD).
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
================================================== ======================
When you say you live in the real world, which one are you referring to?

It could be the things the others have said. It could also be that combind
with the color depth resolution of your graphics card set to lower than 24
bit.
bg

"Doug Kanter" wrote in message
...
Every now and then on the web, I'll see photos which contain a large area
of
color that was supposed to change smoothly from, say, dark red to light
red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number
things,
where you're supposed to change from one paint color to another. What
causes
this? I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure it
never
happens to my pictures.

Doug Kanter wrote:
Every now and then on the web, I'll see photos which contain a large area of
color that was supposed to change smoothly from, say, dark red to light red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number things,
where you're supposed to change from one paint color to another. What causes
this? I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure it never
happens to my pictures.

Hi...

Most likely gif's; or very highly compressed jpg's.

You (unlike the net storage space or download speep problems)
should have little or no trouble with storage space, so
simply save yours in uncompressed format. Or very very
little compression if you must.

Ken

"BG250" wrote in message
...
It could be the things the others have said. It could also be that combind
with the color depth resolution of your graphics card set to lower than 24
bit.
bg

In that case, I should see this problem with ALL the photos I view on this
machine. But, I don't.

Doug Kanter wrote:

Every now and then on the web, I'll see photos which contain a large area of
color that was supposed to change smoothly from, say, dark red to light red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number things,
where you're supposed to change from one paint color to another. What causes
this? I just bought a digital camera, and if it's in any way caused by
camera technique or choice of shooting options, I'd like to be sure it never
happens to my pictures.



Sounds to me like either your display is set to only 16 bit colour, so you don't
get smooth transitions from one shade to the next, or the bit depth of the image
is only 16.

--
Ben Thomas
Opinions, conclusions, and other information in this message that do not
relate to the official business of my firm shall be understood as neither
given nor endorsed by it.

"Gisle Hannemyr" wrote in message
...


To avoid format-induced defects, capture in camera RAW and do all your
post-processing using a non-lossy image format. (E.g.: PNG, TIFF or
PSD).

Unfortunately, my job is interfering with my play time, so I haven't had a
chance to read the entire manual. But if the specs are any indication, it
says it saves in JPG format, but no mention of RAW. But, that's OK. I shot a
few pictures this morning in HQ mode and printed them. Pretty nice quality
for a tiny camera (Olympus Stylus 300). I'm thinking that I'll switch to SHQ
mode permanently after I pick up a couple of 256mb xD cards.

Kibo informs me that "Doug Kanter" stated
that:

Every now and then on the web, I'll see photos which contain a large area of
color that was supposed to change smoothly from, say, dark red to light red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number things,
where you're supposed to change from one paint color to another.

The term for that effect is 'posterisation'.

What causes
this?

The most common reasons are (1) overly-drastic tonal manipulation of a
JPEG original shot, or (2) excessive compression of the web version of
the shot.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Kibo informs me that "Doug Kanter" stated
that:

Every now and then on the web, I'll see photos which contain a large area of
color that was supposed to change smoothly from, say, dark red to light red,
based on the angle of the lighting. Instead, it appears to change in zones
or chunks, almost like the outlines you see on those paint-by-number things,
where you're supposed to change from one paint color to another.

The term for that effect is 'posterisation'.

What causes
this?

The most common reasons are (1) overly-drastic tonal manipulation of a
JPEG original shot, or (2) excessive compression of the web version of
the shot.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------