RE: filmscanners: Setting screen gamma problem

[Jawed Ashraf <Jawed@cupidity.force9.co.uk>]

Julian, I'm surprised no-one has given you a decent answer yet.  I'm going to 
launch-in, risking life and limb as a newbie to this list...

I believe that by creating a JPEG of your wedge and embedding within it a 
reference to the sRGB profile, you have told Internet Explorer to translate 
the linear RGB steps into something that the *eye* perceives as linear (even 
without an embedded sRGB profile, I have this feeling that JPEG is close to a 
2.2 gamma - can someone confirm this?).  This assumes that the monitor is 
set-up properly, i.e.:

- contrast set to *roughly* maximum (so that the brightest white of a web page 
is as bright as can be comfortably accepted, and below the point at which the 
monitor starts to blow-out highlights, and produce acid fringes around 
highlights)

- brightness set so that RGB 0 appears as black as the picture tube/ambient 
light will allow for (some picture tubes are disconcertingly "bright" even 
with the monitor turned off!: especially conventional shadow masks - LCDs, for 
all their faults, often have very deep blacks)

- the display adaptor (graphics card) has been set to its default gamma (if it 
hasn't your life is gonna be miserable!!!)

- Windows has been supplied with a monitor profile specific to your monitor

If you're being a perfectionist you use some kind of profiling/calibration 
software, to tweak the monitor profile.  I'm happy to use Adobe Gamma, which 
is a pretty good first cut.

It so happens that your wedge appears to have even steps from black to white - 
both here at work (Dell-badged 17" Mitsubishi natural flat Trinitron-type 
tube) and at home (Iiyama 19" Mitsubishi natural flat tube).  So in my view 
you have succeeded in creating a wedge that will look right in Internet 
Explorer running on Windows.

If the browser isn't IE, or the browser is running on a Mac, then the image 
will look wrong.  (Note, IE doesn't decode sRGB accurately - it produces 
slightly too-dark images - but the error is way below the problem you seem to 
be having.)

As a little experiment, you can try to produce a GIF file using this wedge.  
You should find that it is hopelessly dark in the shadow region, because GIF 
doesn't support a profile (I believe).

Pity I don't have a web address handy that goes through all this in some 
detail.   The page I saw showed a GIF and a JPEG side by side and explained 
how the profile in the JPEG allowed it to be seen "neutrally", despite the 
fact that both files contained steps defined by the same intervals.

If you're using Windows, your monitor will be operating at gamma 2.2, roughly 
(my Iiyama runs slightly higher, 2.25ish).  If you have Adobe Gamma (see 
Control Panel in Windows) and run through the wizard, it will allow you to 
create a profile which you can save and use in place of your monitor profile - 
you never know, your monitor may not have been delivered with a profile, or 
you may not have installed it (still got the floppy?).

In theory Windows should be using its default monitor profile of gamma 2.2, if 
you didn't install the profile that came with the monitor.  I'd be very 
surprised if you have bought a monitor/video card combination for which gamma 
2.2 isn't very close to what you need.

Hope this helps.

Jawed

>===== Original Message From Julian Robinson <julian@austarmetro.com.au> =====
>Sorry to be difficult, but I don't believe that this is correct, and this
[snippage]