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All renders have slight graininess (both Eevee and Cycles) #113719

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opened 2023-10-14 14:34:48 +02:00 by TomSpicer · 8 comments
TomSpicer commented 2023-10-14 14:34:48 +02:00
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System Information
Tested on Asus Rog G752VS
Operating system: Linux Mint 21.2
Graphics card: NVIDIA Corporation GP104BM [GeForce GTX 1070 Mobile]

Blender Version
Broken: 3.6.4 (2023-09-25 13:24), Blender 4.1.0 - Alpha ( October 13, 16:03:29 , 4050b0d6df )

Any render has graininess (high frequency inconsistent pixel brightness), also with Eeevee, even rendering just a background or an emissive plane with no lights in the scene.

Exact steps for others to reproduce the error

With a default startup, change the background color to something like (0,1,0) to make the graininess clearer when enhancing the rendered image in an image editor.

Problem seems absent when using "AgX" for "Viewport transform" in Blender 4.1.0 - Alpha ( October 13, 16:03:29 , 4050b0d6df ) but present for other modes and all modes from older Blender versions.

To see the graininess with a naked eye, you'll need to enhance the image, like in GIMP as illustrated.

**System Information** Tested on Asus Rog G752VS Operating system: Linux Mint 21.2 Graphics card: NVIDIA Corporation GP104BM [GeForce GTX 1070 Mobile] **Blender Version** Broken: 3.6.4 (2023-09-25 13:24), Blender 4.1.0 - Alpha ( October 13, 16:03:29 , 4050b0d6dfdb ) Any render has graininess (high frequency inconsistent pixel brightness), also with Eeevee, even rendering just a background or an emissive plane with no lights in the scene. **Exact steps for others to reproduce the error** With a default startup, change the background color to something like (0,1,0) to make the graininess clearer when enhancing the rendered image in an image editor. Problem seems absent when using "AgX" for "Viewport transform" in Blender 4.1.0 - Alpha ( October 13, 16:03:29 , 4050b0d6dfdb ) but present for other modes and all modes from older Blender versions. To see the graininess with a naked eye, you'll need to enhance the image, like in GIMP as illustrated.
render - background - enhancing in gimp.png
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render - emissive plane - enhancing in gimp 2.png
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render - emissive plane.png
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test.blend
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render - emissive plane - enhancing in gimp 1.png
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render - background.png
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render - background - enhancing in gimp.png render - emissive plane - enhancing in gimp 2.png render - emissive plane.png render - emissive plane - enhancing in gimp 1.png render - background.png
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 labels 2023-10-14 14:34:49 +02:00
Alaska commented 2023-10-14 15:41:56 +02:00
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Blender applies dithering to the imageby default to reduce banding. This may be the issue you're experiencing.

To turn off dithering:

  1. Open the Properties Editor.
  2. Go to the Output tab.
  3. In the Post Processing tab, turn dithering down to 0.

Does this help/resolve your issue?

Blender applies dithering to the imageby default to reduce banding. This may be the issue you're experiencing. To turn off dithering: 1. Open the Properties Editor. 2. Go to the `Output` tab. 3. In the `Post Processing` tab, turn dithering down to 0. Does this help/resolve your issue?
Alaska added
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 labels 2023-10-14 15:42:06 +02:00
TomSpicer commented 2023-10-14 15:51:16 +02:00
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Blender applies dithering to the imageby default to reduce banding. This may be the issue you're experiencing.

To turn off dithering:

  1. Open the Properties Editor.
  2. Go to the Output tab.
  3. In the Post Processing tab, turn dithering down to 0.

Does this help/resolve your issue?

Why yes, you seem to have found the feature which causes the issue: setting dithering to 0 does seem to eliminate the graininess. However, I don't think this should be happening even with having default dithering. Dithering shouldn't impact flat colors. For example if only a single color background is rendered, or a flat plane with a single color emissive material like here, there's no two or more distinct colored pixels involved which a dithering filter would convert to a grainy noise for banding removal purposes.
So it seems to me like dithering filter code has a bug or limitation to properly deal with flat shaded features in the render: one may want to have dithering On for it to be applied to any gradients in the render, while also needing to have flat shaded features in the render, without one impacting the quality of the other.

As a reference, I'm providing all the dithering methods the image editor GIMP has. Out of all the options, only "Random" seems to add random graininess to flat colored features. Maybe Blender is using a similar algorithm, but I'm not sure why, something like Floyd-Steinberg or Blue Noise seems to make more sense.

> Blender applies dithering to the imageby default to reduce banding. This may be the issue you're experiencing. > > To turn off dithering: > 1. Open the Properties Editor. > 2. Go to the `Output` tab. > 3. In the `Post Processing` tab, turn dithering down to 0. > > Does this help/resolve your issue? Why yes, you seem to have found the feature which causes the issue: setting dithering to 0 does seem to eliminate the graininess. However, I don't think this should be happening even with having default dithering. Dithering shouldn't impact flat colors. For example if only a single color background is rendered, or a flat plane with a single color emissive material like here, there's no two or more distinct colored pixels involved which a dithering filter would convert to a grainy noise for banding removal purposes. So it seems to me like dithering filter code has a bug or limitation to properly deal with flat shaded features in the render: one may want to have dithering On for it to be applied to any gradients in the render, while also needing to have flat shaded features in the render, without one impacting the quality of the other. As a reference, I'm providing all the dithering methods the image editor GIMP has. Out of all the options, only "Random" seems to add random graininess to flat colored features. Maybe Blender is using a similar algorithm, but I'm not sure why, something like Floyd-Steinberg or Blue Noise seems to make more sense.
dithered - random.png
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dithered - bayer.png
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dithered - blue noise.png
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dithered - floyd steinberg.png
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dithered - arithmetic add.png
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gimp dither settings.png
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dithered - arithmetic xor.png
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original.png
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dithered - random.png dithered - bayer.png dithered - blue noise.png dithered - floyd steinberg.png dithered - arithmetic add.png gimp dither settings.png dithered - arithmetic xor.png original.png
ugorek commented 2023-10-14 19:21:27 +02:00
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I also noticed this strange pattern in my renders and had no idea where it came from or how to get rid of it. Turns out it was render.dither_intensity, thanks.
1.gif

I also noticed this strange pattern in my renders and had no idea where it came from or how to get rid of it. Turns out it was `render.dither_intensity`, thanks. ![1.gif](/attachments/c72a3655-f09b-4ef9-9628-839184a82e76)
1.gif
68 MiB
TomSpicer commented 2023-10-14 19:28:56 +02:00
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I also noticed this strange pattern in my renders and had no idea where it came from or how to get rid of it. Turns out it was render.dither_intensity, thanks.
1.gif

Sounds like a relatively new feature that has been aded and enabled silently , I don't remember this artifact before.

> I also noticed this strange pattern in my renders and had no idea where it came from or how to get rid of it. Turns out it was `render.dither_intensity`, thanks. > ![1.gif](/attachments/c72a3655-f09b-4ef9-9628-839184a82e76) Sounds like a relatively new feature that has been aded and enabled silently , I don't remember this artifact before.
Alaska commented 2023-10-15 04:35:33 +02:00
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Changing to "Needs information from Developers". The graininess is caused by dithering. And the dithering can be turned off. However, the behavior of the dither appears to be weird according to the reports from you two. So I'd like a developer that works in this area to comment on this.

Changing to "Needs information from Developers". The graininess is caused by dithering. And the dithering can be turned off. However, the behavior of the dither appears to be weird according to the reports from you two. So I'd like a developer that works in this area to comment on this.
Jesse Yurkovich commented 2023-10-15 05:58:22 +02:00
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Just chiming in with the history: the dithering feature has existed for quite some time but it was first set to 1.0 in Blender 2.80 as part of #54943 (302fea6b61). It was 0.0 in prior versions.

Just chiming in with the history: the dithering feature has existed for quite some time but it was first set to 1.0 in Blender 2.80 as part of #54943 (302fea6b6113f480f5961ddef4a4b967e873f0ef). It was 0.0 in prior versions.
YimingWu commented 2023-10-16 10:12:58 +02:00
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I agree that the dithering algorithm should only affect those areas with changing colors, it should only apply to image regions that has features within some certain thresholds.

I agree that the dithering algorithm should only affect those areas with changing colors, it should only apply to image regions that has features within some certain thresholds.
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Robert Buch commented 2024-05-27 00:40:04 +02:00
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I have programmed some dithering myself as part of an image filter, and I can say that Blender's dithering algorithm makes no sense. It simply adds noise to the image. That's not dithering.

Noise is the simplest (and arguably the best) method of regulating a dithering pattern, since it requires no textures or lookup tables and also doesn't add any repeating, distracting patterns. To implement it properly, the algorithm, assuming it's being applied to one channel of one pixel at a time, needs to do the following: (This algorithm is inspired by dithering in digital audio processing.)

Input: A floating-point value, such as one channel of one pixel, from a rendered or composited image. Let's call it F.

First, calculate the 2 closest values to F that the output image format can use. Let's call them X and Y. For instance, if F = 0.499, and the output is an 8-bit integer, then X = 127 and Y = 128. (8-bit integers range from 0 to 255 while the input F ranges from 0 to 1, so we need to multiply F by 255 first, then round it down to get X, or round it up to get Y.)

Now, calculate how far the scaled F is between X and Y. Let's call that number P. For the example above, we get P = 0.245 (aka 24.5%). We now generate a random number between 0.0 (inclusive) and 1.0 (exclusive). Let's call it R.

And lastly: if P < R then return X else return Y That means there's a 24.5% chance to output X and a 75.5% chance to output Y.

You will notice that if the input number F can be represented exactly with the chosen output format (such as F = 0.0), this algorithm will always return the same output. AS IT SHOULD!

Of course, there is one last thing to consider: The user can control how strong the dithering should be. I do not have a good proposal for properly implementing this. Ideally, it should modify the likelihood that F is dithered at all, as opposed to simply outputting the single closest possible output. So if the dithering setting is low, and F is much closer to X than to Y, then the random number generator is skipped and X is returned as output.

Here is the entire algorithm in one piece of pseudocode:

/// Quantizes a single value (one channel of one pixel) for 8-bit images.
/// param F: The value to quantize for the output image.
int quantize_dithered_8bit(float F)
{
  F *= 255.f;

  if (F <= 0.f) return 0;

  if (F >= 255.f) return 255;

  float X = floor(F);
  float Y = ceil(F);
  float P = F - X;
  float R = random_float(0.f, 1.f);

  if (P < R)
    return X;
  else
    return Y;
}

/// Quantizes a single value (one channel of one pixel) for 16-bit images.
/// param F: The value to quantize for the output image.
int quantize_dithered_16bit(float F)
{
  F *= 65535.f;

  if (F <= 0.f) return 0;

  if (F >= 65535.f) return 65535.f;

  float X = floor(F);
  float Y = ceil(F);
  float P = F - X;
  float R = random_float(0.f, 1.f);

  if (P < R)
    return X;
  else
    return Y;
}

PS: Dithering shouldn't even be an option for floating-point image formats. It simply doesn't make sense.

I have programmed some dithering myself as part of an image filter, and I can say that Blender's dithering algorithm makes no sense. It simply adds noise to the image. That's not dithering. Noise is the simplest (and arguably the best) method of regulating a dithering pattern, since it requires no textures or lookup tables and also doesn't add any repeating, distracting patterns. To implement it *properly*, the algorithm, assuming it's being applied to one channel of one pixel at a time, needs to do the following: *(This algorithm is inspired by dithering in digital audio processing.)* **Input:** A floating-point value, such as one channel of one pixel, from a rendered or composited image. Let's call it `F`. First, calculate the 2 closest values to `F` that the output image format can use. Let's call them `X` and `Y`. For instance, if `F = 0.499`, and the output is an 8-bit integer, then `X = 127` and `Y = 128`. (8-bit integers range from 0 to 255 while the input `F` ranges from 0 to 1, so we need to multiply `F` by 255 first, then round it down to get `X`, or round it up to get `Y`.) Now, calculate how far the scaled `F` is between `X` and `Y`. Let's call that number `P`. For the example above, we get `P = 0.245` (aka 24.5%). We now generate a random number between 0.0 (inclusive) and 1.0 (exclusive). Let's call it `R`. And lastly: `if P < R then return X else return Y` That means there's a 24.5% chance to output X and a 75.5% chance to output Y. You will notice that if the input number `F` can be represented **exactly** with the chosen output format (such as `F = 0.0`), this algorithm will always return the same output. **AS IT SHOULD!** --- Of course, there is one last thing to consider: The user can control how strong the dithering should be. I do not have a good proposal for properly implementing this. Ideally, it should modify the likelihood that `F` is dithered at all, as opposed to simply outputting the single closest possible output. So if the dithering setting is low, and `F` is much closer to `X` than to `Y`, then the random number generator is skipped and `X` is returned as output. --- Here is the entire algorithm in one piece of pseudocode: ```c /// Quantizes a single value (one channel of one pixel) for 8-bit images. /// param F: The value to quantize for the output image. int quantize_dithered_8bit(float F) { F *= 255.f; if (F <= 0.f) return 0; if (F >= 255.f) return 255; float X = floor(F); float Y = ceil(F); float P = F - X; float R = random_float(0.f, 1.f); if (P < R) return X; else return Y; } /// Quantizes a single value (one channel of one pixel) for 16-bit images. /// param F: The value to quantize for the output image. int quantize_dithered_16bit(float F) { F *= 65535.f; if (F <= 0.f) return 0; if (F >= 65535.f) return 65535.f; float X = floor(F); float Y = ceil(F); float P = F - X; float R = random_float(0.f, 1.f); if (P < R) return X; else return Y; } ``` --- PS: Dithering shouldn't even be an option for floating-point image formats. It simply doesn't make sense.
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