Interior renderings too dark

[sandstorm]

Hi all

I am currently doing tests with interior renderings in Luxrender. Independent from the sampler and the tone mapping, I have the impression that the interior renderings are always too dark. I took a look in the gallery and nearly all posted images seem to be very dark to me. Take this as an example:

I just surfed google images search for real interior shots and most of the (professional) shots look brighter, especially the materials which are farer away from the light source. I assume that no additional light sources have been used.

Is Luxrender generally tone mapping interiors too dark or do I just miss the correct settings/light setup? But when I have the wrong setup, why are most of the gallery shots also dark?

Best regards
Martin

Here are the 2 referenced examples.

Luxrender Gallery Example:


Real shot:

[zeealpal]

But the tonemaping settings (Especially Linear) are equivalent to changing the F-Stop, exposure and ISO in a real camera.

If the Sun settings, and any light settings in the Lux image you posted are set to real world values, and the linear tonemapping settings in Lux were set to the same as the camera used to shoot your shot, the results would be the same. I shall post a test myself later today hopefully (Or tomorrow) using a camera, and lux with same settings and light values.

[Abel]

I am currently doing tests with interior renderings in Luxrender. Independent from the sampler and the tone mapping, I have the impression that the interior renderings are always too dark.

With tone mapping, you can make your image as dark or as bright as you like.

most of the (professional) shots look brighter, especially the materials which are farer away from the light source. I assume that no additional light sources have been used.

I find that a surprising assumption - photographers frequently use additional light sources, in particular when it comes to interior shots.

Is Luxrender generally tone mapping interiors too dark or do I just miss the correct settings/light setup?

Just like in real life, LuxRender's interior renderings are likely to feature quite a lot of contrast. If one doesn't want to burn out any details, either one needs to pay a lot of attention to positioning the light sources, or some parts of the image will be darker than intended. In the reference photograph you posted some parts seem to be blown out, which is something many people would want to avoid.

[Carbonflux]

It is difficult to find a simple response to this question because the fundamental assumption behind the idea that a render can be "too dark" is based on the idea that the viewer knows the image is a render. However a photo can also be "too dark" in terms of a viewers expectations.

Even raising this question suggests perhaps a fundamental and very common misunderstanding about the nature of luxrender.

Luxrender is not faking light flow it is attempting to produce a simulation of light based on the best physics it is practical to implement, it is doing this in a high dynamic range contrast space the is beyond normal perception, tonemapping scales that down to a range that can be reproduced by conventional displays, because this contrast range is beyond the range that can be displayed on both ends the idea that a render is "too dark" has no meaning.

The two images presented are not a valid metric for comparison because the lighting is too different.

The real question should be "why don't my renders look like I expect..."

Expectations need to be calibrated to the physics involved in the simulation, the math is either wrong or it is not.

I think direct experience is the best way to move forward should you care to learn more about physically correct rendering

[sandstorm]

Oh sorry. I think I did not formulate my statements precise enough.

I did not mean the whole picture is too dark, but parts of the picture are rendered too dark where other parts are just rendered correctly. I think the photograph is balanced. On the picture from the image gallery it is not the case in my opinion. I just highlighted the two areas where I have doubts. The left square is too dark in my opinion. I assume the grey should represent a white wall. Nevertheless the textures on the drawer are brighter. In contrast to the wall too bright. When I play with tone mapping I can get more white for the wall and too much brightness for the drawer. Or other way round.

I think that is not 100% accuratly calculated in Luxrender.

Best regards
Martin

[Abel]

I did not mean the whole picture is too dark, but parts of the picture are rendered too dark where other parts are just rendered correctly.[...] I assume the grey should represent a white wall.

When looking at the way LuxRender works and comparing the results to other unbiased renderers, I highly doubt you'll find anything that makes a rendered image incorrect locally. And if you're really worried about it, I suggest working with your own scenes instead of looking at somebody else's images and making guesses about the material and lighting setup. Furthermore, when comparing renderings with photographs, please make sure you're looking at photographs as they come straight from a camera as nowadays it is rather common for photographers to use all kinds of post-processing.

I'm not saying that the result you get out of LuxRender is necessarily exactly the ideal image; I find myself regularly adjusting contrast and colours locally, or mixing in lightgroups only in certain areas. But taking a rendering with unknown variables and a photograph with unknown postprocessing, then comparing this against a subjective judgment of correctness is unlikely to yield any insight as to the accuracy of a rendering algorithm.

[sandstorm]

Ok, I just took a photo with my SLR (Sony Alpha 700) and did not any postprocessing in Lightroom.
When you have a look at the backside, the brightness just fades slightly from left to right. The books in the shelf have bright colors.

sDSC4784_0001.jpg (57.9 KiB) Viewed 947 times

Now let us have a look on an image I just rendered. Take a look on the brightness on the backwall. I see that it gets darker earlier than on my photo. So if I want to make the wall in the back brighter, the walls close to the camera get an overdose of brightness.

scene.00017.jpg (26.35 KiB) Viewed 947 times

I did a search on the forum. Let us take a look on the following picture. Luxrender and another renderer (Thea) gets compared. The color of the kitchen perfectly visualizes what I refer to. The color of the Luxrender is dark and the one of Thea is what I would expect.


Please take this thread as feedback and not as criticism. Maybe I am wrong and the addressed behavior of Luxrender is correct. I am curious about other opinions on this.

Best regards
Martin

[SATtva]

I did a search on the forum. Let us take a look on the following picture. Luxrender and another renderer (Thea) gets compared. The color of the kitchen perfectly visualizes what I refer to. The color of the Luxrender is dark and the one of Thea is what I would expect.

I have no idea how one supposed to compare two rendering engines directly without configuring materials and tonemapping absolutely identically, and these images show huge variations in these settings (even white point is different). I'm sorry, but this comparison is bogus.

Considering the darkening, i don't see any here, for example.

[Meelis]

1. Did you actually notice the mirror frame color vs wall color. Why isn't the wall white really??

2. MLT / ERPT mode renders have in start (when render is not finished), darker shadows and overburned highlights. That gets balanced in 10k S/p and up

3. Tonemapping makes all the difference (you can tonemap RGB 0.5 gray to white)

4. RGB 0.8 should be plently of white.

5. Then you have different materials and how they reflect light.

6. It's like you want to expect same quality lighting with Trust PowerCam 820 flash


Like you can get with pro studio lighting