 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 12/02/2010 11:26 AM, clipka wrote:
> Am 02.12.2010 01:01, schrieb Jaap Frank:
>
>> That's odd, because for me the 3.6 side is correct and the 3.7 side is
>> far too bright.
>
> Actually /that/ is odd.
However, regardless of what the reason might be for RGB mapping to
physically linear brightness on his monitor (while in most other cases
the mapping is exponential), this is still the beauty of gamma
correction (when applied properly): He can still set up his assumed and
display gammas in POV-Ray so that rgb 0.5 looks on his display as
physically 50% bright, design his scene that way, distribute the
resulting PNG, and the what-is-supposed-to-be-50%-gray will look like
that on someone else's display as well.
Without any gamma information what looks on his monitor as perfectly
50% gray will look significantly darker on someone else's monitor. The
whole purpose for gamma information is to make the image look the same
in all systems.
So while it might be odd (regardless of what the reason for it might
be), it shouldn't be a problem.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Warp <war### [at] tag povrayorg> wrote:
> On 12/02/2010 11:26 AM, clipka wrote:
> > Am 02.12.2010 01:01, schrieb Jaap Frank:
> >
> >> That's odd, because for me the 3.6 side is correct and the 3.7 side is
> >> far too bright.
> >
> > Actually /that/ is odd.
>
> However, regardless of what the reason might be for RGB mapping to
> physically linear brightness on his monitor (while in most other cases
> the mapping is exponential), this is still the beauty of gamma
> correction (when applied properly): He can still set up his assumed and
> display gammas in POV-Ray so that rgb 0.5 looks on his display as
> physically 50% bright, design his scene that way, distribute the
> resulting PNG, and the what-is-supposed-to-be-50%-gray will look like
> that on someone else's display as well.
>
> Without any gamma information what looks on his monitor as perfectly
> 50% gray will look significantly darker on someone else's monitor. The
> whole purpose for gamma information is to make the image look the same
> in all systems.
>
> So while it might be odd (regardless of what the reason for it might
> be), it shouldn't be a problem.
There seems some confusion here about two ways of approaching gamma. Gamma in
the sense of how a monitor must be calibrated to match absolute physical
brightness levels on a display, paper, inks etc, and gamma in the sense of the
*relative* distribution of tonal values from highlights to midtones to shade to
shadow to black, what Photoshop calls "curves" or what POV has called
"assumed_gamma". It seems, too, from my preliminary tests, that POV is
sacrificing one for the other. It's been almost impossible so far, working
within the defaults of 3.7, to get pictures that don't seem washed out and flat,
as the gradient example suggests they would since the fine gradations in the
darker range seem lost. I'm curious to see how the sample scenes will turn out.
It is perfectly possible and even essential in image processing to adjust the
*relative* distribution of tones. usually to add depth to a picture, and still
set gamma correction according to the color profile so that it can be seen
equally well in another medium or display. It doesn't seem to be possible though
to have gamma correction without color profiles.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 12/1/2010 2:45 PM, Warp wrote:
> With my monitor the photoshop/pov36 part (at the left) has the same
> brightness somewhere between the second-to-last and third-to-last square,
> while the pov37 part (at the right) as the same brightness somewhere in
> the middle, as it should.
>
>
Oddly, I get the exact opposite result ... The left half of the image
matches brightness around the middle. The right half matches in the
second or third from the top.
--
~Mike
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Am 02.12.2010 23:14, schrieb Stephen Klebs:
> clipka<ano### [at] anonymousorg> wrote:
>
>> On most displays, image "gammachecker_3.6.png" will show a chrome sphere
>> on a checkered plane, but there's something wrong here: The checkering
>> shouldn't be there - the plain grey tiles have a brightness of 0.5,
>> while the striped tiles have alternating lines of 0.0 black and 1.0
>> white, so should appear just as bright as the grey if you squint your
>> eyes; and in indeed both tiles appear to have the same brightness in the
>> reflection, where anti-aliasing computes the correct result.
>
> Your gammachecker_3.6 is fascinating. Is the scene file floating around
> somewhere. I assume from the title it's done in 3.6 -- if that makes any
> difference.
It's not floating around yet, but maybe it's worth adding it to the
sample scenes, if only for demonstration purposes.
> I don't really understand how this tests gamma, though, which in practical
> terms, for how I use it, has to do with the relative relation of highlight and
> midtones and shade and shadow, or in Photoshop terms, "curves."
It doesn't test the "curves" ("tone mapping"?) "gamma" thing - what it
does check is whether the purely technical thing called "gamma
correction" is set up correctly (in which case you shouldn't see any
checkered plane anywhere); however, I originally designed it as a
demonstrator for why you should do proper gamma handling; as for the
name, I just couldn't resist the pun.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
____________________________________________________
"Warp" schreef in bericht news:4cf762ae@news.povray.org...
On 12/02/2010 02:01 AM, Jaap Frank wrote:
> That's odd, because for me the 3.6 side is correct and the 3.7 side is
> far too bright.
> I've a rather new HD LCD TFT monitor (about 6 months) and adjusted it
> conform the windows 7 system with brightness and contrast followed by
> color shade correction.
> Further the monitor of my laptop (Acer Aspire, 1 year old, crystal clear
> display) shows exactly the same picture. Both are driven by the NVidia
> card inside the laptop, so they should be the same and for /me/ they
> are. The pictures are displayed by Windows Live Mail.
Note that at least with some LCD displays (especially on some laptops)
the angle from which you look at the screen affects the brightness. For
example, if I look at the image I posted in a MacBook laptop, I can
"tune" the "gamma correction" of the display by tilting the screen back
or forth (thus changing the vertical angle from which I look at the
screen). At some angles it looks like the brightness of the sides
correspond to the center of the 3.6 gradient (and thus the 3.7 gradient
is too bright), while at other angles it looks like they correspond to
the center of the 3.7 gradient (and thus the 3.6 gradient looks too
dark). (And everything in-between, of course.) This tells me that the
screen on this laptop is an *extremely* poor tool to determine which one
is correct (if either), because I can change it by simply looking at it
from a higher or a lower angle.
I do understand, however, that many of the more modern and expensive
LCD displays don't suffer from this problem (at least not as badly).
If I had a working camera I could take photos to corroborate these
findings, but unfortunately I don't.
_____________________________________________________________-
So I did some physical training. I tilted my display screens in any
direction you can imagine, even held them up side down and on their sides,
but while the light impression change with extreem angles, the result is
always the same, 3.6 halfway the gradient and 3.7 somewhere around the
second and third from the dark side. So the problem couldn't be the tilting
angle.
Yve wrote somewhere in this thread that you can choose the color space. I
found it and choose another possibility, but it didn't change much. It's now
a tiny fraction in favor of the 3.7 side. For those who want to experiment
with it:
Windows 7 (and probably Vista): Control Panel > Appearances &
Personalisation > Screen Resolution > Advanced Settings > Color Management
(> Advanced > Calibrate Display).
Win XP: Search your Screen Resolution in Display, the rest is identical.
In 7 there are different Color spaces, but I think that the ICC profiles
(these are for displays) are the only ones you can use. Maybe Yve can
comment on that. In 7 there are two of theme and in XP there is one choice.
If you want to calibrate your screen then use the last part between the
braces (7 only).
So, somewhat wiser, but not further. The next thing I tried was the color
gamma of the video card. NVidia gives the possibility to change the gamma
per color. Because I haven't a picture for the colors I first open't Paint
Shop Pro 6 and in Files > Preferences > Monitor gamma there are three color
bars and a B&W-bar, so you can adjust the gamma's. These values I used in
the NVideo program and check it with PSP6 again. In PSP these are now all
around one value, so my monitors are correctly calibrated.
Back to the picture of Warp: No change at all. Still 3.6 is correct and 3.7
is not correct.
My conclusion is that the problem lies somewhere else and is NOT a problem
of the monitors. In another computer with a rather expensive BenQ monitor
(LCD) the results are exactly the same (Win XP and another NVidia card).
Can anyone check my results and answer here?
Jaap Frank
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
_________________________________________________
"Ive" schreef in bericht news:4cf6fed2$1@news.povray.org...
On 02.12.2010 01:01, Jaap Frank wrote:
> ....
Trust me, Warp is correct and if you see it different there is something
screwed up with your display system. One cannot *perfectly* calibrate a
display without usage of some external hardware but for, let's say
hobbyist usage, there are quite a lot tools (and web-pages) around that
allow for visual adjustment but all of them boil down to something
similar Warp has shown.
_________________________________________________
Thanks for the fast reaction. Please read my reaction on the comment of
Warp too.
_______________________________________________________
> I'm wondering if the default 3.7 approach is correcting the values for a
> 2.2 gamma display in the file, while the display system thinks it gets
.....
A.1. but the actual value can be adjusted by the display_gamma setting
with the recommended default of 2.2 (unless you know what you are doing ;)
B.1. but the actual value can be adjusted by the file_gamma setting with
the recommended default of 2.2 (unless you know what you are doing ;-P)
and the exception of high dynamic range formats being always encoded
linear (as they should be by definition).
C.2. is true for POV-Ray 3.7 AND 3.6 and PNG input format except when no
gamma chunk was present when POV-Ray 3.6 did apply no correction at all
(see below).
C.1. is true for POV-Ray 3.7 and any other format than PNG
BUT POV-Ray 3.6 did use the gamma encoded values internally directly
without converting them to linear color space and this was plain wrong!
________________________________________________________
Then I did understand it right. Now I'm sure about it, thank you.
_______________________________________________
-Ive (and sorry for sending the mail - this happens to me all the time,
I really should learn how to use Thunderbird)
__________________________________________________
Don't bother about that personal email, it has happened to me too.
Jaap Frank
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
_______________________________________________
"clipka" schreef in bericht news:4cf7665a$1@news.povray.org...
Am 02.12.2010 01:01, schrieb Jaap Frank:
> That's odd, because for me the 3.6 side is correct and the 3.7 side is
> far too bright.
Actually /that/ is odd.
_____________________________________________
Please read my reaction on the comment of Warp about the monitors.
_____________________________________________
> By the way, the challenge from clipka is for me a perfect gradient from
> 0,0 to 1,1 in the XY-plane. I suspect that this picture is made with
> 3.7, so that is odd again.
No, it's an image with a "visually linear" gradient created in Photoshop
while working with the sRGB color profile, which I then converted to a
custom color profile with a gamma of 1.0. The challenge is to open this
image in Photoshop and - without converting it to a different color
profile - draw a visually linear gradient over it. I don't know about
newer versions, but in Photoshop 6.0 this will have you end up with a
gradient similar to that created by POV-Ray 3.7.
___________________________________________________
How do you do that: ...draw a visually linear gradient over it. Is there a
choice for this in PSP somewhere?
______________________________________________________
> I'm reading the Gamma Stories for months now and all the same I'm
> confused.
......
_____________________________________________________
Thank you for you thorough explanation. Now I'm sure about the different
gamma settings.
Jaap Frank
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Am 03.12.2010 18:22, schrieb Jaap Frank:
> _______________________________________________
> "clipka" schreef in bericht news:4cf7665a$1@news.povray.org...
>
> Am 02.12.2010 01:01, schrieb Jaap Frank:
>
>> That's odd, because for me the 3.6 side is correct and the 3.7 side is
>> far too bright.
>
> Actually /that/ is odd.
> _____________________________________________
>
> Please read my reaction on the comment of Warp about the monitors.
>
> _____________________________________________
>> By the way, the challenge from clipka is for me a perfect gradient from
>> 0,0 to 1,1 in the XY-plane. I suspect that this picture is made with
>> 3.7, so that is odd again.
>
> No, it's an image with a "visually linear" gradient created in Photoshop
> while working with the sRGB color profile, which I then converted to a
> custom color profile with a gamma of 1.0. The challenge is to open this
> image in Photoshop and - without converting it to a different color
> profile - draw a visually linear gradient over it. I don't know about
> newer versions, but in Photoshop 6.0 this will have you end up with a
> gradient similar to that created by POV-Ray 3.7.
> ___________________________________________________
> How do you do that: ...draw a visually linear gradient over it. Is there
> a choice for this in PSP somewhere?
With normal settings, a standard gradient from black to white should
come close enough to it. Note however that with the color profile
embedded in the image, the result will be strikingly different. My
intention there was to make a point that Photoshop is not a good
benchmark for some stuff.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 03.12.2010 18:03, Jaap Frank wrote:
> My conclusion is that the problem lies somewhere else and is NOT a
> problem of the monitors. In another computer with a rather expensive
> BenQ monitor (LCD) the results are exactly the same (Win XP and another
> NVidia card).
>
You should in any case select sRGB as your working color space as this
is THE standard for the WWW and also JPEG and PNG image files are by
default encoded in sRGB color space and in case they include a different
ICC profile your Windows 7 CMS (err, Color Management System) will
convert them correctly to sRGB.
Then, VERY IMPORTANT, (sorry but I have to use a lot of capital letters
here!) do NOT use the Paint Shop Pro gamma adjustment as THIS IS THE
MOST CRAPPIEST THING I've ever seen (in this regard). Do NOT trust it
and do NOT use it. For nuthin'. NEVER!
OK, do not get me wrong PS Pro is a nice piece of software but it's so
called calibration isn't.
Then go here
http://www.photoscientia.co.uk/Gamma.htm
you may want to read the explanation about gamma (that is quite good)
but please ignore the reasoning for the 1.8 gamma - this is just
outdated (the side is quite old) and I for one did never really agree
with it.
At the bottom of the page choose Gamma 2.2 (and nothing else!) and then
use the color correction panel for your NVidea graphics card and play
with the gamma setting until the *colors* are as close to the gray
background as possible.
This gamma chart is the best one for *visual* gamma adjustment that I am
aware off.
Now you are done ;)
hope this helps
-Ive
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
______________________________________________________
"Ive" schreef in bericht news:4cf951d7$1@news.povray.org...
On 03.12.2010 18:03, Jaap Frank wrote:
> My conclusion is that the problem lies somewhere else and is NOT a
> problem of the monitors. In another computer with a rather expensive
> BenQ monitor (LCD) the results are exactly the same (Win XP and another
> NVidia card).
>
You should in any case select sRGB as your working color space as this
is THE standard for the WWW and also JPEG and PNG image files are by
default encoded in sRGB color space and in case they include a different
ICC profile your Windows 7 CMS (err, Color Management System) will
convert them correctly to sRGB.
Then, VERY IMPORTANT, (sorry but I have to use a lot of capital letters
here!) do NOT use the Paint Shop Pro gamma adjustment as THIS IS THE
MOST CRAPPIEST THING I've ever seen (in this regard). Do NOT trust it
and do NOT use it. For nuthin'. NEVER!
OK, do not get me wrong PS Pro is a nice piece of software but it's so
called calibration isn't.
Then go here
http://www.photoscientia.co.uk/Gamma.htm
you may want to read the explanation about gamma (that is quite good)
but please ignore the reasoning for the 1.8 gamma - this is just
outdated (the side is quite old) and I for one did never really agree
with it.
At the bottom of the page choose Gamma 2.2 (and nothing else!) and then
use the color correction panel for your NVidea graphics card and play
with the gamma setting until the *colors* are as close to the gray
background as possible.
This gamma chart is the best one for *visual* gamma adjustment that I am
aware off.
Now you are done ;)
hope this helps
-Ive
______________________________________________________
Thanks again for the swift reaction Ive. I'm going to work with this. I'll
let you know what the result is.
Jaap Frank
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
|
|
