[ab]

Hi all,

I have three issues with my maxwell scenes that really plaque me:

1: white is not white. The white issue is huge. If one bumps
up the 0 reflection to 240, ..., the noise is fatal + the contrast
also suffers, but as soon as I use normal Levels 180-210,
the walls are gray ??? What's the trick here ?

already went through all the online white materials

2: the light seems to fall off too fast and is not carried throughout
the room, white turns gray too fast.

3: yet I have a loss of contrast in my scene. It always looks washed
out. How do I increase the contrast in scenes ? wall material is not
even white ->

180 for first layer 90% + lambertian +nd 8
210 for second layer 10% + 72 + nd 5


Thank you very much for you help,

ab

ps: I also have to figure out where to post the images. Any recommendations ?

[superbad]

Are you adjusting the camera exposure to make your whites look white? If you open your image in Photoshop and look at the histogram, the curve should go close to the edge of the right side of the scale. You can get a bit more contrast by playing with gamma in MXCL- try using 2.

And try imageshack.us for the image posting.

[ab]

Thank you,

the scene is physical sky only, evening sun,

camera:
FD: 0.46 (still blurry in foreground ?)
shutter: 2.2
fstop:24
focal length: 30

film height: 24
film width: 17.33

ISO 100

Yes, I adjust the exposure, but it just burns it out, does not create
a good contrast:

http://img174.imageshack.us/img174/7571 ... m70ga5.png
http://img249.imageshack.us/img249/9126 ... m70ry5.jpg

I am looking for results such as the ones below:

http://www.evermotion.org/vbulletin/sho ... hp?t=58359


The histogram is pretty flat. I played with the shutter and set gamma to 2 it approaches the one you mentioned, but the colors are all messed up.

The preprocessed image in the thread above has an interesting histogram,
all bunched up in the middle,....

[Mihai]

First, you can switch to additive mode, keep the lambertian bsdf at 100% (nd doesn't matter when using lambertian). For the second bsdf, instead of having an overall reflective layer, make a weightmap for it, so you only get reflective specs on the wall. Although in your images I don't think you would need a second bsdf, just keep the first one. You could set the lamber to about 218.

Second, always start with realistic camera values, fstop of 24 is not so realistic. Set it at something like 4. For an interior render you would need to set it to something like that to get enough light, shutterspeed would be around 60, and ISO about 400.

Third is the post production, in the pic you linked to, it doesn't appear as the surfaces are grey, because the images have been pretty heavily tinted.

[acquiesse]

The colour can be confusing, most real world cameras have a natural white-balance which makes whites look white...

If you think of it logically, a white wall hit by a yellow sun will look yellow... however your brain (and most camera's) will know it is really white and so that is what you see...

Maxwell camera's don't do this, so you need to compensate in photoshop...

Hope this helps

[ab]

thanks guys.

after tinkering around for god knows how long I am starting
to think that this program has a fundamental issue.

White needs to be a 'texture' and then on top of that you can add
all the reflection, ...., this would create a white balance you are
talking about, or a more stable white baseline. Now white is no color, but just a result of all the other colors around it seems.


I seems to be stuck between two choices, and neither sounds appealing:

1: increase the reflection color to 210, 220 and therefore decrease the benchmark, ergo increase the rendering time by a lot.

2: decrease the 0 color to 180 and get gray walls


It should be that the reflection is set 180 and we still get white
walls, such as if you apply materials. The white balancing sounds interesting + the difference between
the reality of a white space and a perceived white space.

[mverta]

Reflection is reflection. If you have a white wall with a semi-glossy clearcoat and there is a yellow object nearby, the highlight will be yellow. Additionally, the yellow object will cast its light onto the wall further coloring it. Maxwell follows the physics of light propagation. Changing the "specular color" like you would in a normal cheat engine, will permanently destroy your chances of returning an accurate render/photorealism. If you tint it one way to compensate for a specific color, you've tweaked out all the other colors.

_Mike

[ab]

Mike,

I see your point. What I meant was that take for
example a red wall, even if there are reflections
in it we will still perceive it as red and we do not add
rendering time.

With the white walls we will not perceive them as white ,
unless we use a color of 220 and above, which leads
to more rendering time -> the white seems to
be tied 1:1 to a very stark increase in rendering time.

just try to lower the color to 180 and you will see how
much faster it will render.

I can get up to a BM of 70 when I use the walls around 180,
but they will be perceived as gray. Do I go to 220, I only
get to a BM of 42, which adds a lot of time, ...

[ab]

[quote][i]Second, always start with realistic camera values, fstop of 24 is not so realistic. Set it at something like 4. For an interior render you would need to set it to something like that to get enough light, shutterspeed would be around 60, and ISO about 400. [/i][/quote]

mihai,

thanks for your tips, I checked them out, but if I set the fstop to 4 I get a lot of blur due to the narrow DOF which an fstop of 24 to 30 will clear up.[/i]

[yves]

If this is the case, either your scene scale is not right or your focus is way too close to your camera... I would check this, it should render nicely then.