.VRIMG with 1.8 Gamma correction?

[peprgb]

Hi,

Im trying to get conversion of a .vrimg to 1.8 but the results are not same as saving directly to 1.8 EXR (or png..etc).

My settings are:
PREFERENCES
Input 2.2
Output 1.0

COLOR MAPPING
Using Reinhard instead of Linear
Gamma 1.8 ("Dont affect colors" unchecked)

Saving to 1.8 EXR is ok making an override of 0.454 when saving. For the .vrimg though, converting with vrimg2exr in ms-dos and applying 1.8 gamma is giving me lighter image than the EXR. I tried some other values in vrimg2exr gamma conversion but no luck

Well, decreasing gamma to 0.454 in photoshop is giving the same result as EXR, but would be cool to get before/directly

Any ideas there?¿

Thank you,

[vlado]

Hm, if you have 1.8 gamma in the color mapping rollout, and "don't affect colors" is off, then that gamma is already burnt into the final .vrimg/.exr file - you don't need to do anything else.

Best regards,
Vlado

[peprgb]

Umm i thought this, but i have these results then (not using .vrimg but .exr):

1_ C. Mapping Gamma=1 Override at 1.8 when saving the EXR
2_ C. Mapping Gamma=1.8 Override at 0.454 when saving the EXR
3_ Gamma 1.8 and Saving through "Raw image" as EXR (so no Override at saving)

The third is much lighter than 1 and 2, and the 1 slightly lighter than 2.

So which is the correct/best method of generating our exr?

When saving through "Vray raw image..." gamma 1.0 is applied? or is applied 2.2 like when saving through Vray frame buffer?

Thanks!!

[vlado]

See my comments below.

1_ C. Mapping Gamma=1 Override at 1.8 when saving the EXR

This will write the data with linear values in the file, but will tag the OpenEXR file with 1.8 gamma, so whatever program you are using to display/read the file must take this tag into account when reading/displaying the file. 3ds Max does take it into account if you select the "Use image's own gamma" option when opening the file.

2_ C. Mapping Gamma=1.8 Override at 0.454 when saving the EXR

I'm just as confused by this as you are

3_ Gamma 1.8 and Saving through "Raw image" as EXR (so no Override at saving)

This will write the data with the gamma 1.8 correction burnt into the colors written to the file itself. No gamma tag will be written to the file, and whatever program you are using to read/display the file must be told not to apply any gamma correction on it (for 3ds Max, you need to override the image gamma with 1.0 when opening it).

So yes, the first and the third method do produce different images.

Best regards,
Vlado

[peprgb]

Thanks for fast reply!!

Well, when we burnt 2.2 in Color mapping and save in EXR we have to Override at 0.454 to compensate the automatically 2.2 that is applied when saving to a HDRI image (haven't we??), so this second test is the same but with 1.8, i burnt 1.8 in color mapping and do 0.454 override (so 0.454x2.2=1), if not i would get 1.8+2.2 correction washed out image...

So the best correct way is to burnt gamma 1.8 (or 2.2...etc) in Color mapping and then saving Overriding with the compensation of 0.454...? With png, jpg LDRI images no need of Overriding, easier

[[all this assuming that we dont touch Outputh in Preferences, so is at 1.0]]

[peprgb]

Ok i forgot this exc. tutorial where he explains that is better to apply/burn the gamma during render, this is, with c. mapping.

So i will use my second (odd for you ) method!!

Thank you,

[Shimakaze]

That's what the "don't affect colors" option is for. It lets the image sampler know that the picture is going to be gamma corrected later and to sample based on the final gamma while still keeping the colors linear.
If you save out as a vrimg or exr file directly with "don't affect colors" selected and open it in Photoshop, then Photoshop should recognize the gamma value and automatically color correct it for you while still keeping the internal color calculations linear (which is a must for compositing)

[peprgb]

Yep, but here i need "Dont affect.." uncheched, since im using Reinhard and therefore i need c. mapping working for the final image. Tried changing to Linear m. (as i always work with it) and the result was terrorific

thanks