this is *NOT* about gamma calibration again (this topic has been 
targeted numerous times and the POV-Ray help section 2.3.4 has some 
excellent write up) this is about brightness and contrast calibration 
witch is AS IMPORTANT as gamma correction.

Attached is a simple POV-Ray script and the image produced by it.

First the brightness (i.e. shadow) adjustment:
The top box is a dark rectangle that consists of 3 rows. You should be 
able to *clearly* identify and separate the four rectangles in the 
bottom row. You should even be able to separate the bottom-left 
rectangle from the center row.
If not you should adjust the *brightness* setting (and only that) of 
your monitor until you do.

The contrast (i.e. highlight) adjustment:
The bottom box is a bright rectangle that also consists of 3 rows. Again 
you should be able to *clearly* identify and separate the four 
rectangles in the bottom row. And (again) you should even be able to 
separate the bottom-left rectangle from the center row.
If not you should adjust the *contrast* setting (and only that) of your 
monitor until you do.

If you do even see the four rectangles within the top row of both - the 
shadow and highlight box - your are either lucky with your equipment or 
a quite rich person who has spend a lot of money for your display ;)

If you are not able to adjust your display to *clearly* see the 4 shades 
in the bottom row within both boxes, well, you should at least be aware 
that you will have 'problems' in judging your own work and also the work 
made by others.

I hope this will help and the 3rd part of monitor calibration - besides 
the transfer function (i.e. gamma correction) highlight/shadow 
adjustment as targeted within this post - would be color calibration 
(and also the most difficult one). All three of them are equally important.

-Ive

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Attachments:
Download 'calibration1.png' (4 KB) Download 'us-ascii' (3 KB)

Preview of image 'calibration1.png'

> If you do even see the four rectangles within the top row of both - the
> shadow and highlight box - your are either lucky with your equipment or
> a quite rich person who has spend a lot of money for your display ;)

And extremely good eye-sight!  The difference between grey level 254 and 
253 will only give a delta-E of about 0.35 (in CIELAB space), it's 
generally assumed that a delta-E of 1.0 is "just visible".  I suspect a 
lot of people who can "see" the separate boxes actually are seeing them 
because of incorrectly calibrated monitors (or viewing a cheap LCD 
slightly off axis).

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Am 21.03.2011 12:36, schrieb scott:
> And extremely good eye-sight! The difference between grey level 254 and
> 253 will only give a delta-E of about 0.35 (in CIELAB space), it's
> generally assumed that a delta-E of 1.0 is "just visible". I suspect a
> lot of people who can "see" the separate boxes actually are seeing them
> because of incorrectly calibrated monitors (or viewing a cheap LCD
> slightly off axis).

Quite Wikipedia: http://en.wikipedia.org/wiki/Color_difference

"a ΔE of under 1.0 is supposed to be indistinguishable unless the 
samples are adjacent to one another."

Note the "unless the samples are adjacent to one another".

E.g. for medical display systems it is (in Germany) a requirement for 
the monitor to be able to separate even the top rows and (believe it or 
not) there are people who do see the difference without any problems.


But did you even care to read my post?
Where did I say that it is expected that you see the different boxes in 
the *top* row?
Do you think it is a good idea to confuse people while I'm trying to be 
helpful?
Are those rhetorical questions?

-Ive

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> Do you think it is a good idea to confuse people while I'm trying to be
> helpful?

My point was that if you can see the difference it is *most likely* that 
your monitor is calibrated badly, not that you happen to have a very 
good calibrated monitor, excellent eye-sight and optimum viewing 
conditions.  I thought it was quite a useful point to make actually.

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On 3/21/2011 3:57, Ive wrote:
> If you are not able to adjust your display to *clearly* see the 4 shades in

Funky. I can see the edges, but I can't see the differences.

-- 
Darren New, San Diego CA, USA (PST)
   "Coding without comments is like
    driving without turn signals."

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> this is *NOT* about gamma calibration again (this topic has been
> targeted numerous times and the POV-Ray help section 2.3.4 has some
> excellent write up) this is about brightness and contrast calibration
> witch is AS IMPORTANT as gamma correction.
>
> Attached is a simple POV-Ray script and the image produced by it.
>
> First the brightness (i.e. shadow) adjustment:
> The top box is a dark rectangle that consists of 3 rows. You should be
> able to *clearly* identify and separate the four rectangles in the
> bottom row. You should even be able to separate the bottom-left
> rectangle from the center row.
> If not you should adjust the *brightness* setting (and only that) of
> your monitor until you do.
>
> The contrast (i.e. highlight) adjustment:
> The bottom box is a bright rectangle that also consists of 3 rows. Again
> you should be able to *clearly* identify and separate the four
> rectangles in the bottom row. And (again) you should even be able to
> separate the bottom-left rectangle from the center row.
> If not you should adjust the *contrast* setting (and only that) of your
> monitor until you do.
>
> If you do even see the four rectangles within the top row of both - the
> shadow and highlight box - your are either lucky with your equipment or
> a quite rich person who has spend a lot of money for your display ;)
>
> If you are not able to adjust your display to *clearly* see the 4 shades
> in the bottom row within both boxes, well, you should at least be aware
> that you will have 'problems' in judging your own work and also the work
> made by others.
>
> I hope this will help and the 3rd part of monitor calibration - besides
> the transfer function (i.e. gamma correction) highlight/shadow
> adjustment as targeted within this post - would be color calibration
> (and also the most difficult one). All three of them are equally important.
>
> -Ive
>
>

Top box, maximum brightness, can't clearly see the individual boxes, 
just hint at them.

Bottom box, usual contrast and I can distinguish the boxes of the top row.

White level is correct, black level is to dark.


Alain

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Ive <ive### [at] lilysoftorg> wrote:
> I hope this will help and the 3rd part of monitor calibration - besides
> the transfer function (i.e. gamma correction) highlight/shadow
> adjustment as targeted within this post - would be color calibration
> (and also the most difficult one). All three of them are equally important.
>
> -Ive

With all your experience in image processing (Lilysoft/IC, etc.) I certainly
appreciate you sharing you knowledge in this area. After I adjusted my settings
I realized that my scenes have been wrong-lit for some time now; especially
noticable in the dark theater setting of the Matinee challenge.

I think I'm close to being calibrated now gamma-wise and
brightness/contrast-wise too, so thanks Ive, this is a big help for me.

-Rob

-------------------------------------------------
www.McGregorFineArt.com

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Am 21.03.2011 23:31, schrieb Robert McGregor:
> With all your experience in image processing (Lilysoft/IC, etc.) I certainly
> appreciate you sharing you knowledge in this area. After I adjusted my settings
> I realized that my scenes have been wrong-lit for some time now; especially
> noticable in the dark theater setting of the Matinee challenge.
>

Thank you Robert for your kind words. Indeed Yours, Trevors and my own 
humble attempt on this lighting challenge (where working with some dim 
lit environment seems a requirement) was the reason to come up with this.

-Ive

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This site is very helpful: http://www.lagom.nl/lcd-test/

Bruno

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