"Web-safe" colours

[Doug Laidlaw]

I tried to grab an image from a Web page the other day. It turned out that
the page was made up of three horizontal bands, and part of the image was
in each. One band was a JPEG, another was a GIF and I have forgotten what
the main page was.

Apart from lining up the parts of the image, there was no discrepancy in
colours between the two formats. Is that what "Web-safe" means? I thought
that it just meant that the colours would be the same in any browser.

Doug.
--
ICQ Number 178748389. Registered Linux User No. 277548.
I find that the harder I work, the more luck I seem to have.
- Thomas Jefferson.

[Spartanicus]

Doug Laidlaw <la******@myaccess.com.au> wrote:

I tried to grab an image from a Web page the other day. It turned out that
the page was made up of three horizontal bands, and part of the image was
in each. One band was a JPEG, another was a GIF and I have forgotten what
the main page was.
Rather off topic here.

Since you've not provided an url for us to check we can only guess, my
guess is that it was done to use both file formats' advantages. Gif (or
preferably png) is better suited for the average computer generated
image, it offers (possibly lossless) compression. Jpeg is intended to be
used with photo realistic images. A composite image that consists of
both computer generated elements and a photo realistic section could be
spliced up and the sections coded in the appropriate format.
Apart from lining up the parts of the image, there was no discrepancy in
colours between the two formats. Is that what "Web-safe" means?
"Web safe" is a term used for images that use an image colour palette of
256 indexed colours. This harks back to the old days when a significant
number of clients could be expected to have a colour capability of just
256 colours, this is relatively rare nowadays. Restricting images to
this 256 colour palette is generally archaic.
I thought
that it just meant that the colours would be the same in any browser.

No such thing as guaranteed the same colours on every client system.

--
Spartanicus

[Doug Laidlaw]

Spartanicus wrote:

Doug Laidlaw <la******@myaccess.com.au> wrote:

I tried to grab an image from a Web page the other day. It turned out
that the page was made up of three horizontal bands, and part of the image
was
in each. One band was a JPEG, another was a GIF and I have forgotten what
the main page was.

Rather off topic here.

Since you've not provided an url for us to check we can only guess, my
guess is that it was done to use both file formats' advantages. Gif (or
preferably png) is better suited for the average computer generated
image, it offers (possibly lossless) compression. Jpeg is intended to be
used with photo realistic images. A composite image that consists of
both computer generated elements and a photo realistic section could be
spliced up and the sections coded in the appropriate format.

Apart from lining up the parts of the image, there was no discrepancy in
colours between the two formats. Is that what "Web-safe" means?

"Web safe" is a term used for images that use an image colour palette of
256 indexed colours. This harks back to the old days when a significant
number of clients could be expected to have a colour capability of just
256 colours, this is relatively rare nowadays. Restricting images to
this 256 colour palette is generally archaic.

I thought
that it just meant that the colours would be the same in any browser.

No such thing as guaranteed the same colours on every client system.

Yes, I knew that the "web-safe" palette was pretty irrelevant these days. I
didn't put my question very well. What I was trying to ask was: Did
"web-safe" guarantee that a colour that was in both file formats would look
exactly the same, whereas a colour outside the palette might not? From
your answer, I assume that I am right off the track here. The URL is
http://www.makinganation.com/ and the image in question is the circular
badge in the top left corner. I am a volunteer at the place described
there. It is actually housed to the right of the steps, behind the lady in
the blue skirt.

Doug L.
--
ICQ Number 178748389. Registered Linux User No. 277548.
Friends are quiet angels who lift us to our feet when our wings have trouble
remembering how to fly.
- Anonymous.

[Jim Moe]

Doug Laidlaw wrote:

I thought that it just meant that the colours would be the same in any browser.

No such thing as guaranteed the same colours on every client system.

Yes, I knew that the "web-safe" palette was pretty irrelevant these days. I
didn't put my question very well. What I was trying to ask was: Did
"web-safe" guarantee that a colour that was in both file formats would look
exactly the same, whereas a colour outside the palette might not?

IIRC, web-safe only applied to the colours used by the "color" and
"bgcolor" attributes, and the CSS equivalents, and has nothing to do with
image display.

--
jmm dash list (at) sohnen-moe (dot) com
(Remove .AXSPAMGN for email)

[Spartanicus]

Doug Laidlaw <la******@myaccess.com.au> wrote:

What I was trying to ask was: Did
"web-safe" guarantee that a colour that was in both file formats would look
exactly the same
No, browsers may get the gamma correction wrong
http://entropymine.com/jason/testbed/gamma/
, whereas a colour outside the palette might not?
No difference/relation.
From
your answer, I assume that I am right off the track here. The URL is
http://www.makinganation.com/ and the image in question is the circular
badge in the top left corner.

The multiple images are the result of what used to be a relatively
popular but fundamentally wrong and flawed way of constructing a web
page. It involves creating the page design in a graphics editor as a
single image, then splicing the image up into multiple images so that
parts can be hyperlinked, then sticking them back together again in a
layout table.

--
Spartanicus

[Alan J. Flavell]

On Fri, 2 Sep 2005, Jim Moe wrote:

IIRC, web-safe only applied to the colours used by the "color" and
"bgcolor" attributes, and the CSS equivalents, and has nothing to do
with image display.

On colour display systems which have only 8-bit colour depth
(fortunately rarely a problem in practice nowadays), there -is- a
problem when the palette of a GIF image does not match the display's
own palette. Indexed PNG (PNG formats were not really being used yet,
back when I recall this being an active topic of discussion) is also
palette-based, and I don't see any reason it shouldn't exhibit the
same problem. This led, amongst other things, to authors complaining
about colour mis-matches between their images and their background
colours.

But it's a topic more for the neighbouring images group, than for
HTML. Nowadays, however, I rarely see the issues discussed -
presumably because those few still using 8-bit colour depth display
systems are assumed to be accustomed to sub-optimal results. My own
notes on the topic go back to 1997, based on even earlier experience,
when things were rather different in practice than they are now - even
if the underlying principles don't change.

best regards

[Toby Inkster]

Jim Moe wrote:

IIRC, web-safe only applied to the colours used by the "color" and
"bgcolor" attributes, and the CSS equivalents, and has nothing to do with
image display.

It applied to any colours you used -- in font and background colours,
images, java applets or elsewhere.

The idea being that on 256-colour displays, if you chose a colour that was
outside that range, you got a dithering effect, that didn't look very
pretty.

On modern displays though, there is no need for dithering, so the "web
safe palette" is a thing of the past.

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact

[rf]

Toby Inkster wrote:

Jim Moe wrote:

IIRC, web-safe only applied to the colours used by the "color" and
"bgcolor" attributes, and the CSS equivalents, and has nothing to do
with image display.

It applied to any colours you used -- in font and background colours,
images, java applets or elsewhere.

The idea being that on 256-colour displays, if you chose a colour
that was outside that range, you got a dithering effect, that didn't
look very pretty.

Not quite.

It had do to with the 256 colour palette, true. But...

When choosing a colour *for each indivudual pixel* if the graphics card
already had that pixel in its [hardware] palette then all well and good. If
however the colour was not in the palette then the driver would search the
palette for a colour that was *nearest* to the new pixels colour. Bor
example nearest to #ffff01 just might be #eeee08, not really near at all,
but the "closest" colour in the current palette.

Paint a single gif (limited to 256 discrete colours) and all is OK. Paint
another gif with a totally different set of 256 colours and all hell breaks
loose. The new gif may override the palette with its colours and the old gif
has to make to with the new colours, which *will* be nothing at all like the
actual colours in that old gif.

In all, 256 colour cards and the resulting pandemodium with palettes and all
were a really very bad idea.

Cheers
Richard.

[geoff_syndicate]

Spartanicus wrote:

Doug Laidlaw <la******@myaccess.com.au> wrote:
<snip>

Apart from lining up the parts of the image, there was no discrepancy in
colours between the two formats. Is that what "Web-safe" means?

"Web safe" is a term used for images that use an image colour palette of
256 indexed colours. This harks back to the old days when a significant
number of clients could be expected to have a colour capability of just
256 colours, this is relatively rare nowadays. Restricting images to
this 256 colour palette is generally archaic.

Actually it's a 216 colour palette. The remaining colours often dither
from one VGA screen to another. If you use the 216 colour palette you
should get pretty consistent results.
In general I would regard this palette as being overly cautious. If you
want to maintain accessibility, use the 'web smart' colour palette, and
retain the colour safe palette for instances of text on blocks of colour.

I thought
that it just meant that the colours would be the same in any browser.

No such thing as guaranteed the same colours on every client system.

True, colours look dramatically different on the Mac. It's a video card
issue, and something you can't second guess.

Geoff