Bad quality background with physical camera

[Christian_Garimberti]

Hi Guys,

maybe i'm doing something wrong, but trying to use a physical camera setting to lower the exposure of the rendering, i found this bad quality result.

See the background. It seems to be a jpg with very high compression!

(attached the rendered image, in the post preview the issue is not so visible)

I attached also a sample image with the settings i used.

2021.0 Same in CPU or GPU rendering.

Best

Chris

[michael_nikelsky]

I am not sure what you are referring to actually, the image looks pretty normal to me. However let me speculate that you are seeing some severe banding in the grayscales of the background, right?

So here is what happens:

Grayscale is always a difficult thing to have on a 8-bit display, there simple are not enough values in to get a really smooth result. That is why dithering can improve the results in some cases but in general you need a higher bit display to fix this.

Then there is also the technical issue that a lot of monitors out there are pretty terrible when it comes to properly displaying grayscale. Things get even worse on these devices if you use a calibration device unless the monitor can store the calibration profile in hardware and has a higher bit (usually 10 bit) LUT inside. If it doesn´t and you end up with a software calibration only (the normal case) which can cause even worse banding on the grayscale since the profile will shift values around. You end up with colors that are better matching a color chart but you are loosing precision.

It is basically the same issue you have with wider gamut colorspaces like AdobeRGB vs sRGB when storing the image in an 8bit image format. You have a wider range of colors to choose from with AdobeRGB but you loose precision in those colors that can be displayed with sRGB.

So the question is: What monitor and color profile are you using?

There is one other caveat with the physical camera: If you don´t use the ACES mode but define your own LUT those curves are 10 bit only. So if the values get shifted around too much you might produce banding artefacts as well.

[Christian_Garimberti]

Hi Michael, what you say is right.

I see banding in the background. I tried on different monitors.

1. Dell H2713HM -> Profile: DELL U2713HM Color Profile, D65 -> https://www.displayspecifications.com/en/model/6a897
2. Dell U2711 -> no specific profile ->https://www.displayspecifications.com/en/model/e1b2749
3. Laptop Hp zbook x360 monitor (Hp 15.6 dreamcolor monitor) -> Profile: HP Zbook Workstation with dreamcolor display_AdobeRGB

On every monitor i can see the banding. 

I tried with your last advice, changing to an ACES mode (tried every 2), but nothing changes.

I tried also to change the environment to avoid a greyscale background. i shifted the white balance to 11000 to have a yellow gradient. Also in this case i see bands.

Another test i did: lowered the exposure of the environment HDRI from the env. material. Resetted the tonemapping in the camera settings. The result is the same.

End of tests......

Tried with another HDRI (the substance sample) and also with this i got bands.

Just to add a note: in the render windows i see a perfect gradient background.

But watching the image from some other devices (ipad and my phone) effectively i didn't see any banding.

So it's definitely my system's fault or settings.

If you know what to check or change or set, would be appreciated.

Thank You

Chris

[michael_nikelsky]

Mhhh..ok did I understand this correctly, in the renderview in VRED it looks ok but when you write out a file and look at it with onother application it doesn`t? 

Did you set any color profile in Windows? 

[Christian_Garimberti]

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@michael_nikelsky wrote:

Mhhh..ok did I understand this correctly, in the renderview in VRED it looks ok but when you write out a file and look at it with onother application it doesn`t? 

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Yes, correct.

I tried in the windows photo viewer and also in photoshop.

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Did you set any color profile in Windows? 

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No, Predefined color profiles are active

[michael_nikelsky · Accepted solution]

Ok, I can actually see the issue now when I load the file into photoshop. It seems there are 2 issues that cause this.

One issue we need to look into is that for some reason the dithering that is done in our viewport is not applied when writing out and image file. So what you have in the file is the actual rendered color converted to the used ICC profile and then converted to 8 bit. Dithering should have added some random noise to the values that cause the banding artefacts to be lower. I am not sure why it is not applied, it should have been.

The other issue is caused by the ICC profile that is set. The default sRGB Profile we have set in the preferences does not handle dark to be caused by the default ICC profile we use, which is the sRGB_IEC61966-2-1_black_scaled.icc default profile which is a widely used standard profile. However additional to converting the values to 8 bit it also changes the whitepoint from D65 (in which sRGB is originally defined) to D50 (which is the standard for ICC profiles). This changes the values that are written to the file. Then a program like photoshop, opens that file and converts these colors back to D65 but this can be lossy.

You can get matching results (except for the dithering, which you can turn off for the viewport in VRED in the Render Settings->Display output->Improve Color Depth) when setting up the same color profile in the VRED preferences for the display and image output as what is used in windows (which ideally would be a profile generated by a colorimeter) and then set the ICC Profile to use to Image ICC Profile. This avoids some of the conversion losses when storing to an 8 bit format. But be aware that not using a standard sRGB format might give different results when the viewing application is not using ICC profiles.

However in general I would recommend to render to EXR from VRED to have a 16bit float format which does not have these issues and postpones the whole conversion issue to a tool like photoshop.

[Christian_Garimberti]

Hi michael,

thank you for your explanations.

Unfortunately i cannot use my xrite calibration tool (it is in office, but i can go to the office...) to have a right calibration.

Unchecking the Improve color depth in the Display output of the render settings i can see banding also in the viewport and this confirm what you say.

I will try to use exr on images when i see this issue.

Do you log the dithering not applied while generating the image output as bug that will be corrected in a next release?

Thank you

Chris

[michael_nikelsky]

Yes, I will look into the dithering issue and log a ticket.

Kind regards

Michael