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.

Download RGBtoLAB 1.03

Ok, this Fuse started off as a really tiny one.  Fusion already has a CSConvert() that does Lab.  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.

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.

Daniel Koch made a ViewShader a while back that does a proper checker underlay for images with straight color, but with this ViewShader, you can go back to using the standard checker underlay if you so choose.

Download AlphaMultiplyDivideVS 1.0

This week, we present six interactive turntables for you to spin. Each one was rendered from a volumetric dataset and can be blended between two views by dragging the mouse vertically. MRI, CT, 3D microscopy and cryomacrotome imaging modalities are all represented here. Check out the bottom right corner for an aptly rendered Bruce Gooch brain.

Each turntable is defined in an XML file that is parsed at run-time to determine the render properties and image asset paths. These assets are streamed in and displayed as needed so the initial download is only about 100KB.

Please view the full post to see the Unity content.

Make sure to right-click on the player and select “Go Fullscreen”.

Example XML:

There has been quite some discussion on WebGL recently. Here is a demo that will show you why we think it is a great technology. It contains an interactive volume renderer that makes use of the new canvas element in HTML 5. A ray marching algorithm applies your transfer function to a texture and renders the volume dataset interactively. Before trying this out, please read the following notes on the limitations concerning different web browsers and graphics cards.

For best performance you should use Google Chrome. It supports WebGL as well as rendering to floating point textures. Firefox should provide the same visual results, but it is considerably slower since we basically have to render twice to achieve the same precision. If you are using Internet Explorer, you are out of luck. Detailed information on how to get WebGL working on different systems can be found here.

Select the head or chameleon dataset to start the demo. If WebGL is enabled and your graphics card is able to compile the necessary shaders, you will see the rendered model within just a few seconds. You can adjust the number of sampling steps along the rays or turn on linear filtering (HiQ) to influence the frame rate and rendering quality. If you experience any problems, please leave a comment below.

Download XML Node Delete 0.5

<ParentNodeName ParentAttributeName=”ParentAttributeValue”>

<NodeName AttributeName=”AttributeValue”>Value</NodeName>

…

</ParentNodeName>

Please note that this program has NOT been extensively tested. It’s probably not too hard to break with bad input. Always double check the output result.

Download Simbiont Fusion 1.05

This is a quick post to show another aspect of the Lazy Susan project: physics based rotation of shaded geometry. This Susan features a clamp that we modeled for a recent surgical simulation. It opens and closes when clicked (with sound!) and uses a tinted reflection map shader to add realism. As usual, click and drag with the mouse to rotate the model. Since this version is geometry-based and not a collection of pre-rendered images like earlier posts, the model can rotated about both the horizontal and vertical axes. Right click and select Go Fullscreen for a close-up view.



Please view the full post to see the Unity content.