[Micha]

Hi,

if I try to convert a HDR to a MXI, the options gamma and burn show no effect in the viewer, only intensity. Is it right?

PS: Will be used the intensity in the emitter shader instead in the viewer in the future?

[albertMaxwell]

Inverse Tonemapping is only available when loading a Image. When loading HDR or MXI has no effect.

You can modify ToneMapping, iso, shutter, fstop and intensity. All of them work.

PS: Will be used the intensity in the emitter shader instead in the viewer in the future?

Yes we are thinking to add a multiplier in emitter for modify MXI intensity from emitter material.

[Micha]

Thanks Albert. Now stay a problem for me. Some HDRIs are very soft with less contrast. I can not change the gamma during the hdr -> mxi convertion. But, if I render the scene, I can not set the gamma lower than 1 and the lighting stay with low contrast. Will it be possible in the future to use a gamma between 0 and 1 in the viewer?

[Mihai]

I still don't understand why you're trying to get better contrast by changing the gamma....

edit: sorry, I'm confusing you and myself, lets just talk of gamma correction

increase gamma= increases the intensity of all pixels
decrease=lower the intensity of all pixels

When you're changing the gamma over the whole image, you are changing the intensity of ALL the pixels, you are not making bright brighter and dark darker at the same time.

[Micha]

Only I can say, some days befor I try to lower the gamma and it was inpossible and I ask me why. In my biased renderer it is no problem.

Let me say, sometimes it can be a question of taste and it is nice to use a special graphical effect like a hard gamma value. Some years befor I had special hard paper for this use in my darkroom. Here an very small quick example of a gamma 1 and 2.2 in a soft hdri environment.
I like the freedom of options for experiments. No limits please.

[Mihai]

I'm curious, did you render that with Vray? with its colormapping features on?

Because what you should have gotten is:

one dark image (left one, correct) and one very bright image (right one, incorrect)

The right one should have really big totally washed out highlights. I think you used the colormapping feature in vray which removed the excessive highlights, making you think higher gamma=less contrast.

[Micha]

Hmm, yes a high gamma value like 2.2 makes the image softer and brighter. Only I adjust the brightness a little bit with ISO or shutter speed in my images here.

Here a color version of Gamma One - a low key image. I adjust the saturation in PS a little. I love the noise.

[Mihai]

Micha, please read my post above, added some stuff.

Just keep in mind:

Increase gamma=brighter image
Decrease gamma=darker image

In none of these cases do you change the contrast.

You decrease the gamma, you will get a darker image, but you will also darken the lighter parts.

[Micha]

This images here are all from Maxwell

Only I can say, it change the impression of the contrast, because the gamma curve is more or less steep. Here look at figure 2.3:
http://www.netnam.vn/unescocourse/computervision/21.htm

I think, we both are right, because the gamma don't change only the brightness. Pixel at level 0 and 255 stay, only the curve between this points change. I know different contrast curves, some cut the high and low values other use something like a S curve.

So, if I change the Gamma and the brightness per ISO/shutter, than I get images like in my examples with different contrast. And what I want to use is sometimes a lower gamma than 1 like in Renderman AIR. I use it seldom, but why not?

[Mihai]

That's funny then, why does the left image have more intensity in the highlights than the right image, with the higher gamma?

Did you let the left image reach more than sl 7? After sl 7 you will see the true luminosity.

I know different contrast curves, some cut the high and low values other use something like a S curve.

Then you're not correcting the gamma...Doing an S curve is not changing the gamma from say 1 to 2. If you are not changing ALL the pixels in the image by the same number, then you are not changing the gamma.

[Micha]

Mihai, I'm confused from all this questions. My small images are from the small real time preview in the maxwell viewer at the same sampling level. I changed the gamma and than the ISO so it looks good for me.

Dennis, only gamma 1 is linear.

[Thomas An.]

When you're changing the gamma over the whole image, you are changing the intensity of ALL the pixels, you are not making bright brighter and dark darker at the same time.

This is true, but the change is not linear.

[Mihai]

I changed the gamma and than the ISO so it looks good for me.

aah, you also changed the ISO Ok, I thought you got that result from just changing the gamma.

Thomas, yes the change ofcourse is not linear, because to change the intensity equally in the image, to show it properly in the monitor, you need to follow the intensity to voltage response curve (the gamma curve).

The result you see on the screen is an equal adjustment of the overall brightness of the image. You do NOT change contrast.

[Micha]

I changed the gamma and than the ISO so it looks good for me.

aah, you also changed the ISO Ok, I thought you got that result from just changing the gamma.

I have written three times, that I changed the ISO also.

[Thomas An.]

Thomas, yes the change ofcourse is not linear, because to change the intensity equally in the image, to show it properly in the monitor, you need to follow the intensity to voltage response curve (the gamma curve).

Gamma only affects the middle values... the pure blacks and pure whites remain untouched. According to your reasoning if we take a black square and adjust the gamma it should become grey..... but it doesn't.