Posterisation type problem

[alfienoakes]

You might have stick with me on this one.

 

I work in LWF, using the gamma correction right at the end, or save to exr, dependent on what I am doing.

 

Now when I render to the VFB, and apply the correction curve to see how the image looks, I get a strange sort of "posterisation" effect on the image. It looks like contouring where the dark areas just havent received enough light. But the image doesnt look to dark.

 

If I then save it out to a JPG file, it smooths these errors out. However, if I remove the curve, and save out to an EXR file, I can really see the contours. If I then save it out to a JPG file again, it does smooth the image out, but they are still visible (see image). Now this might be the fact that I work on an LCD; I havent viewed this yet on a CRT.

 

But, if anyone has any clues as to how I can get rid of this, I would be grateful. I am only worried mainly about animations, as I am concerned I may end up with shimmering walls.

 

I am using IR and LC. Havent tried it with other bounces yet.

 

Regards

[Stephen Thomas]

I would think that this is similar to the problem where you can have more noise in shadow areas too, as demonstrated in Chris Nichols gnomon tut on image sampling. If you are using the latest version of VRay the solution is to change gamma to 2.2 in your colour mapping settings and turn on the adaption only option. This means that the gamma is not applied, but tells vray that it will be, so it can gather the same amount of information from shadowed areas as light areas. Try it and see if it helps.

[Stephen Thomas]

By the way, the sRGB curve being on or off only affects what you see in the frame buffer not the saved image. The gamma is controlled by saving the image using system gamma (set to 1.0) for exr or overriding to 2.2 for jpegs etc.

[alfienoakes]

By the way, the sRGB curve being on or off only affects what you see in the frame buffer not the saved image. The gamma is controlled by saving the image using system gamma (set to 1.0) for exr or overriding to 2.2 for jpegs etc.

 

Yep.. know about that one cheers mate.

 

I will try the colour mapping one for sure, as it does seem a bit weird. Im still not really sure how much of a problem it is though, as I have only just really stumbled across it..!

[alfienoakes]

OK..

 

Downloaded the latest version of Vray, RC5, and tried the settings suggested above.

 

Still get the same "banding" when saved to *.exr format. As mentioned, when converted to JPG, this banding smooths out a heck of a lot, but you can still make it out.

 

Has anyone else seen this, or can reproduce the same "error". I am just using IR and LC, no particularly high settings, and I have only noticed it since working in LWF. It seems to be a lack of light in the darker areas, which I would have lit using vray planes when not working in LWF, hence more light buzzing around, and the problem never showed.

 

Any clues or similar experiences would be welcomed..!

[Craig Ramsay]

Are you using an LCD screen by any chance? I have seen banding like this in some of my images on screen but when I print out it's fine, I think it's down to my dell LCD screens having a pretty poor colour representation... i'll be upgrading them soon because of this.

 

There is an interesting thread about this here:

 

http://www.cgarchitect.com/vb/14490-lcd-vs-crt-vs-5.html#post145950

[Crazy Homeless Guy]

Still get the same "banding" when saved to *.exr format. As mentioned, when converted to JPG, this banding smooths out a heck of a lot, but you can still make it out.

 

what about saving to tiff? ....i'm wondering if the smoothing in the jpeg image is only a result of the lossy nature of jpeg, and the banding is still just as bad.

[Craig Ramsay]

i'm wondering if the smoothing in the jpeg image is only a result of the lossy nature of jpeg, and the banding is still just as bad.

 

Yep I was thinking that myself.

[alfienoakes]

Craig: Was actually reading a thread over on Chaosgroup this morning about that. It would be handy of I could forward the exr file to someone whose monitor is calibrated or not a Dell one to see if it looks as I see it..

 

Travis: I will try that.. see if it works.

 

Cheers

[jvlive]

That's funny. Mine's reverse. I few months back I've had this problem saving to tiffs. Tried png and targa but the same. But it was gone when I used .exr. Not really sure that it was exr that did it, but I stopped having that problem around the same time. I use 64-bit Integer (RGBA)

[alfienoakes]

It is strange.. Its very similar to yours Jvlive, but when I am saving it to EXR it is really noticeable.. like looking at one of those vials with coloured sand in..

 

I will try messing about with tiff's & tga's and see if I can reduce it at all. What did you do to rid your images of this ..?

[MasterZap]

I'm not really seeing much of a problem... you are sure you are not running your display in 16 bit color or something similar??

 

/Z

[Stephen Thomas]

Just out of interest Andy, why are you not using vray planes at the windows to supplement the skylight and what is the connection to LWF. As I understand it these are two different issues. LWF is about not applying gamma correction twice to your bitmaps or not going back and forth between colour spaces to avoid errors. Using planes at the windows is about not having to send out millions of samples to get a good GI solution.

 

Please correct me if I am wrong.

[alfienoakes]

Hakan:

 

It is tricky to see, especially on the JPG interpretations of the file. The EXR file really shows it much much more, on my monitor anyway. And no, I am pretty sure I am not in 16 bit. I cant post the exr file though on this thread. Is there a central area I could dump it so people could see it..? I cant remember

 

seth:

 

LWF is about working in a linear space, so you correct your gamma, but yes, you wouldnt want to correct it twice. LWF has the benefits of making your scenes lighter, allowing you to use less lights in the scene. Less lights means less calculations, and a more realistic solution especially for GI.

 

Also, GI will work easier, as the Vray planes arent blocking the light that comes in from outside. I am sure someone who is an expert on LWF could shoot me down on some of that.. Using planes at the windows is used because the scene is too dark, and you have to supplement the GI with some false lighting, to give you similar results. Its not incorrect using planes though, just a different way.

[jvlive]

... What did you do to rid your images of this ..?

 

That's what's funny Andy, I had these when I was saving my renders to tiff and I got rid of 'em when I started saving to exr. Yours is exr with the effect and you get rid of it when saving to jpegs.