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Corona Renderer includes its own Virtual Frame Buffer (VFB) window and interface that has been tuned to the most common needs of artists and can provide a very decent post-production experience and results.

Corona VFB (Virtual Frame Buffer)

Tone Mapping

Basic

Contrast – Changes contrast - the difference in brightness between light and dark areas of the image. Values greater than 1 increase the image contrast, and values below 1 decrease it.

Photographic Exposure – Changes overall exposure of the image based on the settings of the currently used camera.

Saturation – Controls the overall image saturation, negative values decrease it.

Tint – Sets the overall color tint of the scene. The entire image is multiplied by this color. This can be used both to add and remove color tints from the image. To add a tint, select the color of the tint directly. To remove tint from any rendered object, pick its color using the pick inverse eyedropper in Corona Improved Color Picker.

Vignette – Simulates the real-world camera vignette by darkening the edges of the image.

White Balance – Sets the white balance point using Kelvin temperature, often used in photography. Lower temperature leads to a bluish, cold appearance of the image, while higher temperature leads to a warm appearance.

Curve Control

Advanced Filmic Mapping – Applies highlight compression and shadow saturation control using Filmic S-curve. Allows more control over the curve compared to the basic Filmic operator. When enabled, the output is always in the interval [0, 1] so the bright pixels are compressed.

Curves – Applies custom color mapping curves.

Filmic Mapping – Allows highlight compression and shadow saturation control using Filmic S-curve.

Tone Curve – Allows independent control of different tones of the image - shadows (the darkest areas), darks, light, and highlights (the brightest areas).

Highlight control

Reinhard Highlight compression – Compresses highlights in the image to reduce/remove burned-out areas. Increasing the value removes burned-out areas, and decreasing it amplifies highlights.

Final look

ACES OT (Output Transform) – Applies approximate ACES Output Transform which is consisting of Reference Rendering Transform (RRT) and Output Device Transform (ODT).

LUT – Changing the overall look of the image by applying a predefined LUT.

Bloom and Glare

Size – Increases/decreases bloom and glare size.

Bloom intensity – Increases/decreases bloom intensity.

Glare intensity – Increases/decreases glare intensity.

Threshold – Controls the minimum brightness which is considered for the Bloom and Glare effect. Increasing the threshold applies Bloom and Glare only to the brighter pixels. Reducing it allows the Bloom and Glare effect to be applied to pixels that are less bright.

Color intensity – Controls how saturated the Bloom and Glare effect is. Higher values mean higher saturation.

Color shift – Changes the hue of the coloring added to the Bloom and Glare effect. 

Streak count – Defines the number of streaks for the glare effect. 

Rotation – Rotation of the glare effect in degrees.

Streak blur – Decides whether the glare streaks should be sharper or more blurry.

Custom aperture – Launches an editor which can be used to fine-tune advanced Bloom and Glare options.

Sharpening/Blurring

Sharpen amount – The value that is used to control sharpening.

Sharpen radius – Defines the sharpness radius.

Blur radius – Defines the radius of blur.

Denoising

Denoise amount – The main value that is used to control denoising. It blends between the original (noisy) image and the fully denoised version of the image, where 0 is the original image and 1 is the purely denoised version.

Times

Scene parsing – How long it took to get the data from the native application format to the internal Corona format. Excessive times (more than a few seconds or tens of seconds for complex scenes) can be caused by running out of RAM, using slow network drives, complex scatters and geometry models, etc.

Geometry – How long it took Corona to prepare the geometry for rendering. This includes computing displacement, building, and acceleration structure, and preparing the lights for sampling. Excessive times (more than a few seconds or tens of seconds for complex scenes) are most often caused by using too detailed displacement, using too detailed displacement, using too many textured lights, or running out of memory.

UHD cache precomp – How long it took to calculate UHD cache. The time depends on resolution, scene complexity, and UHD cache settings ( animation preset calculates significantly longer, but it does not flicker in animation).

Rendering – Total elapsed rendering time.

Denoising – How long the denoising took. Denoising is optionally computed after rendering. Its running time is dependent only on resolution (number of pixels) and the number of render elements to be denoised - it has to run from scratch for each element.

Estimated remaining – If any render limit is set (time, passes, or noise level), Corona computes the best possible time estimate. If no limits are set, '—' is shown and the user has to stop the render manually.

TOTAL elapsed – the total elapsed rendering time.

Scene

Primitives unique – Numbers of unique (non-instanced) primitives in the scene. Primitive means a single triangle, hair strand, etc. Each such primitive is stored in the memory, so this number is directly proportional to the RAM usage (1 primitive takes up about 200 Bytes).

Primitives displac. – The number of unique (non-instanced) micro triangles created by displacement in the scene. Each such object takes a certain amount of memory but is generally an order of magnitude smaller than regular triangles.

Primitives inst. – The number of primitives in the scene after instancing allows storing a single object in the memory just once and placing it into the scene multiple times with almost no additional memory usage. This is extremely useful e.g. for forests, grass, etc.

Geometry groups – The number of unique geometry groups in the scene. One geometry group roughly corresponds to one separate mesh/object in the source scene, not counting instanced meshes. This number does not significantly influence the performance/memory usage, with a single exception; high values (thousands and more) can slow down the preprocessing phase.

Instances – Number of geometry groups in the scene after instancing is applied. Each instance takes about 1000 Bytes of memory.

Lights (groups) – The first value is the total number of light-emitting primitives in the scene and the second value is the number of instances that contain these primitives. High values usually mean a scene with complex illumination, where slower rendering is to be expected. Only true light emission counts - neither self-illumination nor Light material with Emit light off.

UHD Cache

Records – Numbers of discrete points in the scene for which the illumination is computed during preprocessing and which are used for the interpolation during rendering. Complex scenes and animations, where higher precision is required, cause this number to increase, which in turn makes the precalculation slower.

Success rate – The percentage of rays that were accelerated using the cache. This is the effectiveness of the cache, e.g. 70% meaning that 7 out of each 10 rays were accelerated. The higher this number, the faster is the rendering as more rays are accelerated.

Performance

Passes total – The total number of passes computed. One pass in Corona means that each pixel received on average 1 sample. The number of passes directly influences the quality of antialiasing, the depth of field, and the motion blur effects. Smaller images accumulate passes faster there are fewer pixels to process. Also if Rays/sample is too high then too much work is spent per pixel, causing the number of passes to stay low, which slows down the antialiasing/depth of field/motion blur computation. A limit for the number of passes can be set in render settings.

Noise level – An estimate of the remaining noise level in the image. A limit for the noise level can be set in render settings, around 2% usually being enough for the final images, 5% for the final images with denoising, and anything higher than that being suitable for the previews.

Rays total – The average number of rays computed per second since the render started. Rays/s is a measure of the brute force computation power of the renderer. Comparing rays/s between different machines is a good way to compare their CPU performance. The number is also higher in simple scenes when using simple materials. A too low number (lower than usual for the machine) can mean problems with CPU overheating, running out of RAM, other CPU utilization problems, or just having too complex materials/shaders.

Rays actual – Number of rays computed in the last second. Rays/s is a measure of the brute force computation power of the renderer. Comparing rays/s between different machines is a good way to compare their CPU performance. The number is also higher in simple scenes when using simple materials. A too low number (lower than usual for the machine) can mean problems with CPU overheating, running out of RAM, other CPU utilization problems, or just having too complex materials/shaders.

Samples actual – Number of pixel samples computed in the last second. This is the rate of how fast the anti-aliasing, depth of field, and motion blur are computed. This number is the rays/s statistic divided by rays/sample.

Rays/sample – How many rays are needed to compute a one-pixel sample. This is the measure of the shading complexity of the scene, with high numbers meaning that a lot of work needs to be done to compute each pixel. This can be caused by using too complex shaders (with ambient occlusion and rounded edges), materials having too high albedo, or using too high GI vs. AA balance.

VFB refresh time – How long the VFB window takes to redraw last time.

Preview denoiser time – How long it took to denoise the VFB image.

Store Current VFB – Stores the contents of the current VFB in the history.

Clear A/B – Disables the history comparison and shows the current render only.

Delete All – Deletes all items from the history and from HDD.

Show with original postprocessing – Shows the stored content with original postprocessing.