Infoseite // gamma understand correctly - for the time people have ...

Frage von rassnik:


Hello dear forum!
Now after I read some tags which are always at gamma / gamma correction, and I actually believed everything is understood to have a better recently, I was told. I will no longer be satisfied with superficial knowledge but have internalized it and for all. I miss this I think only a small detail (hopefully).

the basis of schaubildeswill ich verdeutlichen wie wir ein graues blatt entweder direkt visuell wahrnehmen bzw. über den umweg kamera/monitor. zuerst zum direkten (im schaubild unteren) weg.

soweit ich das bisher verstanden habe...

the direct path:

s.The famous "18% gray card" that we perceive as the mean gray even though they did not consider is linear, because ...

1) ... our eyes have a gamma of about 0.41. ie the 18% gray card, we take (lighter) than ...

b) ... mittelgrau true. (0.41 potenz of 0.18 = 0.5)

the "detour" (above):

s.The gray card ....

3a) ... is taken of a video camera. this mimics the behavior of the video kamere auges after And. ..

2) ... correct the signal with a gamma of 0.45. this is done start from the following:

I would be without these gamma correction for the half of our field of perception, only about 50 gradations are available (with color depth of 8 bits). banding would be favored.
II.das approximately inverse gamma of crt monitors will be compensated. Modern tft's to emulate this behavior.

3b) ... formerly 18% gray card thus resulting in rgb values of R = 127, G = 127, B = 127

5) ... at the presentation on the monitor is by das ..

4) ... the average gamma of 2,2-abgedunktelt rgb values as much to us again, the medium gray map "tricked" is. the points 2 & 4, therefore, about to cut out.

6) ... the gamma correction makes our eyes from this monitor on the gray card is the same as shown with the real. They will lighten And. ..

b) perceived as middle gray.

the problem:

Or so it says in the books. Quite logical and consistent in my opinion. If there were not these damn gamma test charts were ...
This Testcharts want with my assumption, namely, at point 3b (or my whole understanding of it) not seem to fit together.

Here is a



Antwort von soahC:

Unfortunately you can not help piece. but is very interesting, and I'm really looking forward to the answer ...



Antwort von Nightfly!:

This may help you!

The median RGB gray (R = G = B = 127) has in ECI RGB, or are affected with Gamma = 1.8 image processing monitor calibrated
an L *- value of 60

http://www.lb-ag.ch/news/digital/basiccolor/basICCaliCube.pdf

Gruß,
Nightfly!



Antwort von Schleichmichel:

Oops, there it was gone ...

Your monitor is probably no longer the youngest, or generally not designed for such critical tasks.

But there is worse ...



Antwort von rassnik:

thank you in advance for the reply.

@ nightfly
the with the lightness L * value of 60 does not help me really, but thank you

@ creeping michel
With the monitor has little to do. just a calibrated monitor with one of 2,2 GAMM has indeed such a large deviation vs. 186. 127

how does it look after your understanding? 127er Gray would have to be perceived as being medium gray and not 186er, right?

rassnik



Antwort von Axel:

Real Mid Gray - 50% luminance layman's terms - will be seen on the Mac with an actual gamma value of 1.8.
Picture dazu
Der Augenschein bestätigt mir das. Diese Wahrnehmung ist subjective: caused by the gamma correction of our visual apparatus (and other factors in video signal processing). Very nice description, thank you for your presentation. You wrote:

Picture dazu
Der Augenschein bestätigt mir das. Diese Wahrnehmung ist Quote: Picture dazu
Der Augenschein bestätigt mir das. Diese Wahrnehmung ist Suppose we sit in front of a PC dieess gamma test chart at a certain distance and narrowed eyes should be somewhere around a gamma of 2,2 coalesce around (Mac 1.8). the gray area of the corresponding gammas so we perceive as "middle gray". rgb in the fall of this would be a gamma of 2,2 values of (upper row) 186! The bites are extremely illustrated with my signal chain when we rgb values of 127 as "medium gray perceive" knew. Picture dazu
Der Augenschein bestätigt mir das. Diese Wahrnehmung ist

As defined DV chrominance and luminance of each pixel only RGB values of 0/0/0 (black) and 255/255/255 (White), equivalent to 12 8 / 12 8 / 12 8 an absolute mid-gray. Rather, correspond, since we are the center of the spectrum (see so) elsewhere.

Actually, hand me that my technique of some well-educated people has been calibrated. The many adaptations of values relative to other values, I often cause a slight dizziness. So I am more of a What-You-See-Is-What-You-Get type. I just find confusing in the face of this graph, that lead to a gamma correction in the postpro higher values than "1" to darker, more pleasant images. One would indeed expect the opposite (?).

For all those who have trouble understanding the issue of Gamma, the Comparison with brightness and contrast makes sense:

Brightness increases (or vice versa) in DV all RGB values by the same absolute value. May have an impact on the contrast.
Contrast narrow (or extended), the spectrum, so that the darkest values higher (vv) and the brightest lower (vv).
Gamma shifts the average value while maintaining the contrast, but of course with an impact on the overall brightness of the image.

An interesting thread. No idea if I understand it. Request for correction. DIY Together we s.einem correct understanding.



Antwort von Jeronimo93:

hi axel,
times what is still looking at rumkommst.

Strictly speaking, gamma change had contrasting only stop in the shade / middle / highlights different. is a zuwachs bereicht contrast to weigh the contrast in the other area.

small GAMM brightens or darkens gamma> 1 s.wegen functional

pixel high gamma = new value

cheap because it is "pixel" to normalized between 0 and 1 are the following happens:

0.18 High 0.41 = 0.5

0.5 high 2.5 = 0.18

at least approximately. we are of the gray card to medium gray and back again.

rassnik