Anatomical Travelogue Research » Fusion

Color Reduction

Sven — Sat, 24 Dec 2011 16:39:37 +0000

The main purpose of the Color Reduction tool is to maximize the contrast in the color channels of an image. This can improve the input for color segmentation tools as well as the results of color to grayscale conversions. We implemented two different algorithms in order to determine color space transformations that optimize the contrast: Principle Component Analysis (PCA) and Locality Preserving Projections (LPP).

Both methods can be applied to transform or reduce 2-4 input channels to 1-4 output channels, for a single image or a range of images. A secondary image input can be used to supply a weighting mask that determines the influence of each pixel during the color reduction algorithm. Afterwards, the output channels can be normalized and optionally, the color transformation can be encoded in a Fusion 3D LUT.

Download Color Reduction 1.0

Description of methods

The results of PCA and LPP are not necessarily the same since the optimization is based on different criteria. PCA determines the principle components that account for most of the contrast in color space, e.g. if the contrast in the red and green channels is much higher then the contrast in the blue channel, the first channel returned by PCA will be a linear combination of the red and green channel.

In addition, LPP considers the proximity of colors in the image space, e.g. if many yellow pixels are neighbors of green pixels in image space, green and yellow pixels may get the same color in the first channel of LPP. In constrast, red and yellow pixels may get different colors although their distance in the color space is the same (see details on the effect of the LPP weighting factor below).

Comparison of PCA and LPP

The following video shows the effect of PCA and LPP for color to grayscale conversion. The results are compared to simply using the lightness channel of the LAB color space. For better visibility, only the 2D histogram for the red and blue color channels is shown.

In the first step, the color space of the input image is projected onto a line. The orientation of the line and the direction of projection are different for all three methods and result in a different distribution of contrast. In the second step, the line is mapped to the grayscale range and normalized.

While PCA will always find the axis of highest contrast in the color space and is independent of any parameters, the results of LPP depend on a weighting factor.

Effect of the LPP weighting factor

The image below helps to understand the effect of the LPP weighting factor. Internally, the weighting factor is applied to the color space distances of neighboring pixels, so that a higher factor will lower the chance of pixels with different colors to be recognized as neighbors. The example shows the input image which contains dark green, light green, yellow and orange pixels and a simplified red-green histogram.

Although the color space distance in vertical direction is smaller than the distance in horizontal direction, LPP will recognize the neighborhood between light green and yellow pixels as well as the neighborhood between dark green and orange pixels in image space. Therefore, LPP with a low weighting factor will project light green and yellow to the same color as well as dark green and orange to another color. However, after increasing the weighting factor, the color space distances will become more important than the spatial neighborhoods again and the result will be the same as for PCA.

RGB to LAB

Chad — Fri, 18 Nov 2011 20:40:34 +0000

Download RGBtoLAB 1.03

Ok, this Fuse started off as a really tiny one. Fusion already has a CSConvert() that does L a b. So all I have to do is…

if mode == 0 then

out:CSConvert("RGB", "LAB")

else

out:CSConvert("LAB", "RGB")

end

Simple and fast. But the results were a bit… unexpected. So we added a little tweak which has no basis in known color science, it just makes is so that a linear RGB input returns what I think is a linear L output.

So why doesn’t ColorSpace have an Lab button? I don’t know. You can see LAB color in action in the Wand tool, though.

Other options include output a LUT Image only, as if it were a Source tool. Same as the new option on ColorMatrixTransform. You can also choose whether to affect the canvas color or not.

And there was much rejoicing

Chad — Wed, 16 Nov 2011 19:10:59 +0000

Eyeon released Fusion 6.3 last week, and we’ve had a chance to look at some of the new tools and how they would fit in with our tools.

VolumeFog now includes a Schlick single-scattering lighting model.

Download Particle Voxelization for VolumeFog A01

You can render in OpenCL, or fallback to CPU if you need to render a larger volume dataset than you have memory on your OpenCL device. It works nicely, but definitely shows the interface issues with representing 4D data as X,Y,Time,Time. We use Quilt for 4D data, but we’ll have to see if there’s an easy way to get that translated over to VolumeFog. Of course, getting a proper 3D fog texture can be handled nicely by Simbiont.

AlphaDivide and AlphaMultiply provide dead simple color operations, but they’re no faster than our own tool. And unlike the new built-in tools, AlphaDivideMultiply allows you to affect the canvas color, too.

LUT Fuses allow you to analyze and apply LUT images to your footage to simplify various color operations, as well as provide simple interoperability with other applications. They’re also operate in OpenCL if available. We’ve updated ColorMatrixTransform to produce these images. Just 8 pixels can represent all of the possible corrections you can apply with a Color Matrix. We’ll be adding this to more tools soon.

This new version of Fusion also fixes some annoying bugs. It’s now possible to create an interactive LUT macro. Previously, interactivity was limited, you just set the LUT up once and left it. Polylines are now able to evaluate properly at multiple image sizes without randomly evaluating the wrong reference. And a longstanding issue with spline view redraw has apparently been fixed, making it much easier to use in real-world comps.

SimbiontFusion 64-bit released

Matt — Tue, 12 Jul 2011 17:32:26 +0000

We have uploaded a new version of SimbiontFusion that includes the long-awaited 64-bit support. This plugin allows you to render DarkTree procedural textures directly in Fusion. Please note that the plugin was compiled with the Fusion 6.2 SDK and that installation steps have changed for this release, so consult the readme.txt file.

Download Simbiont Fusion 1.05

Material brightness contrast 3D

Matt — Tue, 14 Jun 2011 17:59:34 +0000

We’re releasing another Fusion tool today that has been helpful in our 3D workflows. The tool applies the functionality of Fusion’s brightness contrast tool (BC) to 3D materials. Simple.

We’ve been moving large amounts of image data to the graphics card lately, so this tool allows us to tweak fragment colors without requiring a re-upload for each iteration.

Download Material Brightness Contrast 3D 1.0

Signed Distance

Arun — Wed, 11 May 2011 15:23:59 +0000

The signed distance operator can be quite useful when doing image/voxel data processing based on a pixel’s distance from an iso-surface. This plugin calculates just that. The plugin is implemented using Open CL, so the Open CL program should also be copied into the same directory as the Fuse plugin.

Download Signed Distance Fuse

The tool has inputs to control the position of the iso-surface (Zeropass Threshold) and the number of rasterizing passes (Number of Passes). The output can be a distance value or a 2D – vector pointing towards the closest point in the iso-surface.

Set Color

Chad — Mon, 02 May 2011 22:16:23 +0000

Very simple fuse, this one just fills the canvas with a color.

Download Set Color Fuse

Needed this on a project where I was laying out logos and graphic elements that had to always be a specific color, and the existing workflow with many BG’s was too messy. Normally I would have just tolerated the mess, but this Fuse is simple enough to be made in less than 5 minutes.

Generic Shader addins: Half Lambert, Parallax, NPR Preprocess

Chad — Tue, 26 Apr 2011 18:17:48 +0000

Look! More shaders for the Generic Shader.

Gooch Shading courtesy of the NPR Prepass

New shaders include ColorMatrixTransform, Unit Vector, Dot Product, Half Lambert, Parallax, and NPR Prepass which returns various lighting dot products for use in making NPR effects like the Gooch shader above.

What I’ve done this time is to repackage the .cg file in with the plugin, so you don’t have to add all the new strings if you’re downloading the plugin for the first time. The plugin itself is unchanged, only the .cg shaders changed. I’ve also included the Lit Sphere shader.

NOTE: I’ve changed the indices of the shaders, so the new .cg will break some comps that used the old one. If you want to maintain compatibility, you’ll have to replace the shader number manually. Only affects Length, which went from 7 to 17, Bump Falloff, which went from 1,000,000 to 14, Jitter, which went from 5 to 7, and Lighting Data Debug which moved from 6 to 11.

The plugin and shaders: Download GenericShader3D 1.1

Just the shaders: Download ATGenericShader_f.cg 1.1

A sample comp showing some of the new shaders: Download Generic Shader Sample Comp 3

Bilateral Filter

Sven — Fri, 10 Dec 2010 20:57:45 +0000

Smoothing an image without losing all the edges, that’s what the Bilateral Filter is made for. It basically performs a Gaussian blur not only in the image dimensions, but also on the color intensities. Therefore it will smooth homogeneous areas while at the same time respecting the image’s edges. The following example shows the effect very well.

The current version is for Fusion 6.1 in 64 bit only. It provides the standard bilateral filter as well as the cross bilateral filter for grayscale and color images. DoD and RoI can be used to limit processing to a desired section of the image. Since the exact filter is very slow when applying large filter kernels, calculation in OpenCL with an optional approximation method is implemented as well. First tests on supported graphic cards show a speed up by a factor of 3-5 for OpenCL with default parameters. On gray scale images with large filter sizes, the approximation method can be more than a hundred times faster.

Download Bilateral Filter 1.2

Quilt

Arun — Fri, 29 Oct 2010 19:44:37 +0000

Here’s is a plugin to tile multiple frames into a single output image. We’re calling it “Quilt”. The plugin should be downloaded and copied into one of the fusion plugin directories. We’ve uploaded both the 32 and 64 bit versions for windows.
The plugin provides options to change the start/end frame, the size of the output image and filter to use when the input is re-sized. Also available are provisions to pad the output, trim it and an option to preserve/alter the input’s aspect.
The tool should tile all the input frames into the output in an “optimal” layout. It should be useful when you want a overall view of all the frames you’re interested in.

Download Quilt 1.0