Blackmagic Cintel Scanner User Manual Noise Reduction
Based on the noise reduction controls in the ‘color’ page, Resolve FX noise reduction has two types of GPU-accelerated noise reduction designed to subdue noise in problematic clips. Both methods of noise reduction can be used separately or together, in varying amounts depending on the needs of the particular material you’re working on.
Temporal NR Controls
The temporal NR controls analyze images across multiple frames to isolate noise from detail. Motion estimation settings let you exclude moving subjects from this operation to prevent unwanted motion artifacts.
Frames Either Side: The number of frames on either side of the current frame that you want averaged to separate detail from the noise. You can choose between 0 and 5 frames. 0 applies no frame averaging; higher values apply more frame averaging, at the expense of being significantly more computationally intensive. A higher frame setting may yield a better analysis, but may also yield unwanted artifacts if there are fast-moving images in the frame. A value of 1 may yield better results for fast-moving images. If you need to use higher frame values, but see artifacts, you can also try adjusting the motion threshold to fix the issue.
Motion Est. Type: Picks the method DaVinci Resolve uses to detect motion in the image. The default, ‘faster’, is less processor intensive, but less accurate. Choosing ‘better’ can effectively exclude motion more accurately, but is more processor intensive. None lets you disable motion estimation altogether, resulting in the application of temporal NR to the entire image.
Motion Range: Three settings, ‘small’, ‘medium’, and ‘large’, let you set the speed of motion that motion estimation should expect to exclude. A ‘small’ setting assumes slow-moving subjects with little or no motion blur, allowing temporal NR to affect more of the image at a given motion threshold setting. A ‘large’ setting assumes fast motion with blur occupying a larger area of the image, which excludes more of the image from temporal NR at the same motion threshold setting. Choose the setting that gives you the best compromise between reducing noise and the introduction of motion artifacts when adjusting the motion threshold parameter.
Temporal Threshold Controls
The temporal threshold parameters allow you to control which image characteristics get more or less noise reduction.
Luma threshold: Lets you determine how much or how little temporal NR to apply to the luma component of the image. The range is 0–100, where 0 applies no noise reduction at all, and 100 is the maximum amount. Too high a setting may eliminate fine detail from the image.
Chroma Threshold: Determines how much temporal NR os applied to the chroma component of the image. The range is 0–100, where 0 applies no noise reduction at all, and 100 is the maximum amount. Too high a setting may eliminate fine color detail from the image. However, you may find you can raise the chroma threshold higher than the luma threshold with less noticeable artifacting.
Gang Luma Chroma: Ordinarily, the luma and chroma threshold parameters are ganged together so that adjusting one adjusts both. However, disabling this checkbox ungangs these parameters, allowing you to adjust different noise reduction amounts to each component of the image, depending on where the noise happens to be worst.
Motion: Defines the threshold separating which moving pixels are in motion (above this threshold) versus which moving pixels are static (below this threshold). Using motion estimation, temporal NR is not applied to regions of the image that fall above this threshold, to prevent motion artifacts by not applying frame-averaging to parts of the image that are in motion. Lower values omit more of the image from temporal NR by considering more subtle movements. Higher values apply temporal NR to more of the image by requiring faster motion for exclusion. You can choose between 0 and 100, where 0 applies temporal NR to no pixels, and 100 applies temporal NR to all pixels. The default value is 50, which is a suitable compromise for many clips. Be aware that if you set too high a motion threshold, you may see artifacts in moving parts of the image.
Blend: Lets you dissolve between the image as it’s being affected by the temporal NR parameters (at 0.0) and the image with no noise reduction (100.0). This parameter lets you easily split the difference when using aggressive temporal noise reduction.
Spatial NR Controls
The spatial NR controls let you smooth out regions of high-frequency noise throughout the image, while attempting to avoid softening by preserving detail. It’s effective for reducing noise that temporal NR can’t.
Mode: The ‘mode’ menu lets you switch spatial NR between three different algorithms. All three modes of operation use the same controls, so you can switch between modes using the same settings to compare your results.
Faster: Uses a computationally lightweight method of noise reduction that’s good at lower settings, but may produce artifacts when applied at higher values.
Better: Switches the spatial NR controls to use a higher quality algorithm that produces greatly superior results to Faster, at the expense of being more processor intensive to render and not allowing you to decouple the luma and chroma threshold sliders for individual adjustments to each color component.
Enhanced: Does a significantly better job preserving image sharpness and detail when raising the spatial threshold sliders to eliminate noise. This improvement is particularly apparent when the spatial threshold sliders are raised to high values (what constitutes ‘high’ varies with the image you’re working on). At lower values, the improvement may be more subtle when compared to the ‘better’ mode, which is less processor intensive than the computationally expensive ‘enhanced’ setting. Additionally, ‘enhanced’ lets you decouple the luma and chroma threshold sliders so you can add different noise reduction amounts to each color component, as the image requires.
Radius: Options include ‘large’, ‘medium’, and ‘small’. A smaller radius offers greater real-time performance and can provide good quality when using low luma and chroma threshold values. However, you may see more aliasing in regions of detail when using low NR threshold values. Setting ‘radius’ to be progressively larger results in higher quality within areas of greater visual detail at high luma and chroma threshold values, at the expense of slower performance. An NR radius of ‘medium’ should provide suitable quality for most images when using medium NR threshold settings. As with many operations, there’s an adjustable tradeoff between quality and speed.
Spatial Threshold Controls
The spatial threshold parameters allow you to control which image characteristics get more or less noise reduction.
Luma: Lets you determine how much or how little noise reduction to apply to the luma component of the image. The range is 0–100, where 0 applies no noise reduction at all, and 100 is the maximum amount. Too high a setting may eliminate fine detail from the image.
Chroma: Lets you determine how much or how little noise reduction to apply to the chroma component of the image by smoothing out regions of high-frequency noise while attempting to preserve the sharpness of significant edge details. The range is 0–100, where 0 applies no noise reduction at all, and 100 is the maximum amount. Too high a setting may eliminate fine color detail from the image. However, you may find you can raise the chroma threshold higher than the luma threshold with less noticeable artifacting.
Gang Luma Chroma: Ordinarily, the luma and chroma threshold parameters are ganged together so that adjusting one adjusts both. However, you can ungang these parameters to adjust different amounts of noise reduction to each component of the image. For example, if an image softens too much at a certain level of noise reduction, but you find more color speckling than luma noise, you can lower the luma threshold to preserve detail while raising the chroma threshold to eliminate color noise.
Blend: Lets you dissolve between the image as it’s being affected by the spatial NR parameters (at 0.0) and the image with no noise reduction (100.0). This parameter lets you easily split the difference when using aggressive spatial noise reduction.
Global Blend
Blend: Lets you dissolve between the image with no noise reduction (1.0) and the image with both spatial NR and temporal NR at their current settings (0.0).
Using Noise Reduction
The following procedure suggests a method of using the noise reduction (NR) parameters to achieve a controlled result.
Applying noise reduction to an image:
Enable temporal NR by choosing 1 to 5 frames from the ‘number of frames’ menu. Keep in mind that more frames dramatically increase the render time of this effect, while it may or may not significantly improve the result, depending on your material.
Choose options from the ‘motion est. type’ and ‘motion range’ menus corresponding to how much motion is in the image. If there’s a lot of motion, you may need to choose ‘better’ and ‘large’. If there’s not very much motion, lesser settings may suffice.
With luma and chroma threshold linked, slowly raise either parameter until you just start to see a reduction in noise within nonmoving areas. Then make smaller adjustments to determine the maximum amount you can add without creating artifacts or overly softening detail.
If there’s obviously more chroma than luma noise in the image, you can disable luma and chroma linking at a satisfactory level of luma noise reduction, and then raise the chroma threshold to address color speckling in the picture.
Suppose you’re not satisfied with the tradeoff between the maximum possible threshold of noise reduction and the prevention of motion artifacts. In that case, you may want to adjust the motion threshold setting, lowering it to omit more of the motion from the noise reduction operation, or raising it to include more motion. If you’re still not satisfied, you can also try better ‘motion est. type’ and ‘motion range’ settings. Keep in mind that the strength of temporal NR is to reduce noise in unmoving parts of the image. When you’ve achieved the best tradeoff between noise reduction in the still areas and avoidance of motion artifacts in the moving areas of the image, it’s time to turn to spatial NR to further eliminate noise throughout the rest of the picture.
Enable spatial NR by raising either the luma or chroma threshold parameters, which are linked by default, until you strike a suitable balance between the reduction of noise and an unwanted increase in image softness.
It’s recommended to choose the Enhanced option from the spatial NR mode pop-up, as it will yield the best possible results. However, this can be processor-intensive, so if you need better real-time performance, you can switch the mode to Faster and compare results.
If there’s obviously more chroma than luma noise in the image, you can disable luma and chroma linking at a satisfactory level of luma noise reduction, and then raise the chroma threshold to apply more aggressive spatial NR to address color speckling in the picture.
If you’ve had to use a high spatial NR luma or chroma threshold setting to reduce noise visibly, and areas of detail look a bit chunky or aliased, you can choose a larger setting from the ‘radius’ menu to enable a more detailed analysis of the scene. This will result in higher visual quality, but larger NR radius settings are more processor-intensive and may reduce real-time performance if you don’t have adequate GPU resources available to your system.
If you’ve found suitable noise reduction settings, but the result is too aggressive and makes the image appear too processed, you can try raising the spatial NR and/or temporal NR blend parameters to fade between the noise reduction added by each set of controls, and the image as it was before you added noise reduction.
Try Applying Temporal NR First, then Applying Spatial NR
Because temporal NR analyzes multiple frames for its noise isolation, it tends to be better at preserving detail accurately in regions of the image where there’s little motion. If you try applying temporal NR first and get a successful result, even if only in part of the image, you may reduce how much spatial NR you have to apply, thus improving the overall quality of your final result.
Keep in mind that while temporal NR does a great job in unmoving parts of an image but is less effective when dealing with subjects in motion, spatial NR can reduce noise everywhere in the frame falling below its threshold, even when there’s motion. Ultimately, a combination of the two is almost always going to be a winning combination.
Spatial NR Radius, How Large Should You Go?
Larger NR radius settings can dramatically improve the quality of high-detail regions in shots where you’re using aggressive spatial noise reduction, but it’s not necessary to always jump to the large radius setting, which provides the highest precision. In many cases, when evaluating an image that you’re applying noise reduction to, you may not be able to perceive the additional quality. You’ll waste processing time on an unnecessary level of correction.
It’s a good idea to evaluate the full-frame image on a large enough display to see the noise you’re working on within the viewing context of the intended audience. Zooming really far into a clip while applying noise reduction may encourage you to use higher quality settings than are necessary because an excessively enlarged detail of an image lets you see subtle changes that you wouldn’t notice at actual size.
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