Re: png colour gamut
Re: png colour gamut
I got involved because they were having trouble understanding
colour gamuts
and the images were coming out dark and muted. Well that was easy
to solve,
and I showed them about assigning different colour spaces in
Photoshop. But
then I thought it strange that they made their end archiving format
png.
They claimed this hadn't been a problem in the past and it was space
efficient.
So I tried to do some research on png and that just produced more
questions.
Do I have this right? A png file may EITHER be in sRGB or it
contains chroma
values and gamma values but not both (ie not in sRGB and chroma/
gamma)?
From Adobe's Help files: "PNG format supports RGB, Indexed Color,
Grayscale, and Bitmap mode images without alpha channels."
PNG is lossless compression, and PNG-24 supports 24-bit color and 256
levels of transparency. PNG-8 supports 8-bit color and 1 level of
transparency.
So I opened one of their source files (.tif in eyelike ebu) and
used SAVE AS
and saved it as a png. I wasn't given any options as to colour gamuts.
So here's my question. If I have it right about pngs being either
in sRGB or
containing chroma and gamma values, which is Photoshop using with
"save as"?
And if Photoshop SAVE AS does use sRGB, does it use relative
colorimetric
to do this conversion?
I believe PNG-24 is in whatever color space you were working in, but
it doesn't support profile embedding; so you're at the mercy of the
users' browsers. If you're talking about PNG-8 then you have some
options for how the 8-bit pallet is built.
And which png option is it using in SAVE FOR WEB.
You have access to all the options in the dialogue - PNG-8, PNG-24,
transparency, dither, pallet adaptation, interlacing, matting...
And lastly, does anyone else think that going to the trouble of
using an
eyelike digital back and archiving tens of thousands of museum quality
images and only save them in png format is not a good idea?
According to Adobe's Help, not all browsers support PNG; so they'll
wanna' do some testing. But on the whole it seems like a pretty fair
idea. With JPEG you can post a profile on the site and code things so
that color management savvy browsers will interpret the colors
correctly - don't know if PNG supports that. I guess the other
question to look at is how efficient is the compression. A quick test
I did here looks like PNG really mashes the file down.
Rich Apollo
G7 Certified Expert
Adobe Certified Expert, Photoshop
314-344-1144
email@hidden
www.prioritylitho.com
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