Matlab Display Volume

Volume Display

Display volumes with volshow for performant, high quality volume display. Display isosurface meshes, triangulations, and surfaces using images.ui.graphics.Surface rather than isosurface for more performant, higher quality mesh display with more responsive interactions for meshes of all sizes.

When to Use

• User asks to create a GUI, app, dashboard, or interactive tool for volume, isosurface, or surface mesh display
• User wants ROIs, annotations, or other lines and shapes plotted on top of the volume or surface mesh
• User wants to display labeled data or other overlay volumes on top of a volume

When NOT to Use

• User does not have the Image Processing Toolbox — fall back to isosurface + patch, but recommend volshow for better performance.

Medical Image Volumes

When the user has the Medical Imaging Toolbox, use medicalVolume to load DICOM/NIfTI/NRRD files, then call the volshow method on that object. This automatically sets the spatial Transformation and SpatialUnits from the file metadata. All other patterns in this skill (Viewer, overlays, annotations, streaming, app building) still apply — only the entry point differs.

medVol = medicalVolume("brain.nii");
obj = volshow(medVol);

Key Objects

Utilities: linkviewers(viewers) synchronizes camera motion across multiple Viewers. title(viewer, "text") sets the Viewer title.

Workflow

1. Create Viewer — call viewer3d() or viewer3d(parent) for app contexts
2. Add Volume — call volshow(V, Parent=viewer) to display volumetric data
3. (Optional) Add surfaces — call images.ui.graphics.Surface(viewer, Data=tri) for mesh display
4. (Optional) Add annotations — call uidraw(volObj, "line") for interactive ROIs
5. (Optional) Configure callbacks — set CameraMovedFcn, AnnotationMovedFcn, or ObjectClickedFcn on the Viewer
6. Update data — set obj.Data = newV to stream; use waitfor(viewer,"Busy",false) for synchronization

Legacy Patterns to Avoid

Patterns

Standard Volume Display

Simple cases of volume display can call volshow without specifying a parent. All name-value arguments can be set as properties on the Volume object, and the volume data can be updated by setting the Data property.

obj = volshow(V);

Choose DisplayRangeMode based on the data type and value range:

% 12-bit medical volume
obj = volshow(V, DisplayRangeMode="12-bit");

% Manual window/level
obj = volshow(V, DisplayRangeMode="manual", DisplayRange=[200 1200]);

Set RenderingStyle to control how voxel data is visualized. See the dedicated Rendering Styles section below for detailed guidance.

Choosing a Colormap — Select based on data content:

obj = volshow(V, Colormap=gray(256));

Choosing an Alphamap — The alphamap is a 256×1 vector mapping normalized intensity [0, 1] to opacity [0, 1]. It controls which structures are visible vs. transparent. The default is a cubic ramp (x.^3), which suppresses low-intensity background while revealing bright structures.

% Gaussian alphamap centered at 60% intensity (width 10%)
x = linspace(0, 1, 256)';
alpha = exp(-((x - 0.6).^2) / (2*0.1^2));
obj = volshow(V, Alphamap=alpha, Colormap=gray(256));

% Hard threshold — only show voxels above 30% of the display range
alpha = double(linspace(0, 1, 256)' > 0.3);
obj = volshow(V, Alphamap=alpha);

For per-voxel opacity control (e.g., masking specific regions regardless of intensity), set the AlphaData property to a volume the same size as Data with values in [0, 1]:

obj = volshow(V, AlphaData=double(regionMask));

When displaying an overlay of a mask, semantic segmentation, or other volume data on top of another volume, use the OverlayData property of the Volume object and the corresponding name-value arguments OverlayColormap, OverlayAlpha, OverlayRenderingStyle, OverlayDisplayRange, and OverlayDisplayRangeMode to adjust the overlay display. This is a faster option than blending the overlay with the volume and updating the Data property, or adding a second Volume object to the Viewer. The default properties for overlay display are tuned to support semantic labels, but can be adjusted to support continuous data for other purposes.

obj = volshow(V, OverlayData=mask);

If spatial referencing information is available, include it in the Transformation name-value argument. Build an imref3d from voxel spacing and volume size, or use an affinetform3d for arbitrary affine transforms. When using medicalVolume, the volshow method sets the transformation automatically from file metadata.

% From voxel spacing (e.g., [0.5 0.5 1.0] mm)
R = imref3d(size(V), 0.5, 0.5, 1.0);
obj = volshow(V, Transformation=R);

% From an affine matrix
tform = affinetform3d(A);
obj = volshow(V, Transformation=tform);

For large volumes that exceed GPU texture memory (typically > 2048³ voxels) or are too large to fit in RAM, create a multilevel blockedImage and pass it to volshow. The makeMultiLevel3D function creates a resolution pyramid for progressive rendering — the Viewer loads coarse levels first, then refines as the camera settles.

bim = blockedImage(V, BlockSize=[512,512,512]);
mbim = makeMultiLevel3D(bim, Scales=[2 4 8]);
volshow(mbim);

Use Scales to control the downsampling factors. Each scale creates a level at 1/N resolution. For very large volumes (e.g., 4096³+), include more scales (e.g., [2 4 8 16]). Smaller volumes that just exceed the texture limit need fewer levels (e.g., [2 4]). The BlockSize should match or be a multiple of the GPU texture block size (512³ is a good default).

Surface Mesh Display

Displaying surface meshes using images.ui.graphics.Surface offers better rendering and interactive performance over isosurface + patch. Pass a triangulation object as Data and an N×3 matrix of per-vertex RGB colors as Color.

% tri = triangulation(...), cpoints = N-by-3 vertex colors
viewer = viewer3d(BackgroundGradient="off", BackgroundColor="white");
obj = images.ui.graphics.Surface(viewer, Data=tri, Color=cpoints);

When possible, displaying the mesh with the default Alpha of 1.0 is recommended for optimal performance. You can call images.ui.graphics.Surface multiple times to add multiple objects to the scene and the objects will be sorted and rendered spatially correct with depth peeling. When objects are transparent, more render passes are required and the performance will decrease.

Surface meshes can be displayed together with volumes in the same Viewer.

viewer = viewer3d();
volObj = volshow(V, Parent=viewer);
surfObj = images.ui.graphics.Surface(viewer, Data=tri);

When updating the position or size of a Surface, it is much faster to update the Transformation property than to re-set Data with a new triangulation. Use drawnow to flush the graphics queue between frames (this is appropriate for Surface animation — only volume streaming requires waitfor).

viewer = viewer3d(BackgroundGradient="off", BackgroundColor="white");
obj = images.ui.graphics.Surface(viewer, Data=tri, Color=cpoints);

% Disable auto camera position update
viewer.CameraPositionMode = "manual";

% Animate the surface moving in the z direction
for idx = 1:100
    tform = transltform3d(0, 0, idx);
    obj.Transformation = tform;
    drawnow;
end

Rendering Styles

The RenderingStyle property on the Volume object controls how voxel data is visualized. Choose the style based on what structures need to be visible.

Maximum Intensity Projection (MIP) — Projects the brightest voxel along each viewing ray onto the screen. Ideal for vascular imaging (angiography), fluorescence microscopy, or any data where bright structures are the signal of interest.

obj = volshow(V, RenderingStyle="MaximumIntensityProjection");

Gradient Opacity — Makes large homogeneous regions (low gradient) transparent while preserving regions with sharp intensity transitions (high gradient). This lets you see through bulk tissue to reveal boundaries and edges within the volume.

obj = volshow(V, RenderingStyle="GradientOpacity");

Cinematic Rendering — State-of-the-art photorealistic rendering with global illumination, ambient occlusion, and soft shadows. Produces the highest quality visualization for solid structures like bone in CT scans. More computationally expensive but delivers publication-quality results.

obj = volshow(V, RenderingStyle="CinematicRendering");

Other styles:

% Isosurface at a specific threshold (e.g., bone in CT)
obj = volshow(V, RenderingStyle="Isosurface", IsosurfaceValue=300);

% Orthogonal slice planes
obj = volshow(V, RenderingStyle="SlicePlanes");

Streaming Volumes

When updating the display, reuse objects whenever possible. Avoid using the clear method on the Viewer when you are going to re-add the same types of objects — always reuse. Keep the Volume object returned by volshow and update its Data property. Volume data is loaded asynchronously, so drawnow may return before rendering completes. Use waitfor on the Viewer's Busy property to block until the data has finished loading.

viewer = viewer3d();
obj = volshow([], Parent=viewer);

for idx = 1:10
    V = rand([512,512,512]);
    obj.Data = V;
    waitfor(viewer, "Busy", false);
end

Generating Animations

When generating animations or capturing frames, use getframe and pass the Viewer (parent of the Volume object) as the first argument. The Viewer waits until all pending updates have processed before capturing, which guarantees each frame is fully rendered.

viewer = viewer3d();
obj = volshow([], Parent=viewer);

frames = cell(1, 100);
for idx = 1:100
    V = rand([512,512,512]);
    obj.Data = V;
    frames{idx} = getframe(viewer);
end

Adding Annotations on Volume

When displaying interactive or a small number of annotations on the volume, use the uidraw function to start interactively drawing or to programmatically place an annotation.

uidraw is ideal for fewer than 100 annotations. Omitting Position starts interactive drawing. When Label is not specified, the ROI displays a standard measurement (e.g., distance for lines). Set SpatialUnits on the Viewer to include units in the measurement display.

obj = volshow(V);
viewer = obj.Parent;
viewer.SpatialUnits = "mm";

% Interactive drawing (user places the line)
roi = uidraw(obj, "line", Color=[1,0,0]);

% Programmatic placement (no interaction required)
roi2 = uidraw(obj, "point", Position=[20,20,50], Color=[0,0,1], Label="Point of Interest");

% Multi-point polyline from a position matrix (each row is a point)
pos = [20,20,50; 50,60,75; 50,80,100];
roi3 = uidraw(obj, "polyline", Position=pos, Color=[0,1,0]);

% Make an annotation static (disable further interaction)
set(roi3, "Interactions", "none");

Responding to User Interactivity

Add function handles to callback properties on the Viewer to respond to user interaction. CameraMovedFcn fires after the camera is moved. AnnotationMovedFcn fires after the user interactively moves or reshapes an annotation. ObjectClickedFcn fires after the user clicks and releases in the Viewer without dragging (a click-and-drag initiates the default interaction, typically panning). Use the event data to determine which object was clicked.

V = rand([100,100,100]);
obj = volshow(V);
viewer = obj.Parent;
% Draw a rectangle ROI interactively
roi = uidraw(obj, "point", Color=[0,1,0], Label="ROI");
% Listen for movement and display the position
viewer.AnnotationMovedFcn = @(~,evt) fprintf("ROI Position: [%.1f, %.1f, %.1f]\n", evt.Position);

App Building

When building apps, call viewer3d(parent) to create a Viewer parented to a uigridlayout, then call volshow with that Viewer as the parent. Create the Volume object eagerly at construction time with empty data ([]) — this avoids conditional logic later and lets you simply update obj.Data when data becomes available. Only defer Volume creation if the app supports switching between fundamentally different display modes (e.g., volume vs. surface-only).

Use a standard app classdef (see matlab-building-apps skill) with the following in createComponents:

% Inside createComponents(app) — viewer3d parented to grid layout
app.GridLayout = uigridlayout(app.UIFigure, [1 1]);
app.GridLayout.RowHeight = {"fit"};
app.GridLayout.ColumnWidth = {"fit"};

app.Viewer = viewer3d(app.GridLayout);
title(app.Viewer, "App Display");
app.Viewer.Layout.Row = 1;
app.Viewer.Layout.Column = 1;

% Create Volume eagerly with empty data
app.Volume = volshow([], Parent=app.Viewer);

Then update data later with app.Volume.Data = im;.

Adding a Colorbar to a Volume App

Since the Viewer does not natively support a colorbar, place an invisible uiaxes with a colorbar in an adjacent grid column. Set Colormap and CLim on the axes to match the Volume object, then call colorbar on that axes.

fig = uifigure(Name="Volume with Colorbar", Position=[100 100 800 500]);
gl = uigridlayout(fig, [1 2]);
gl.ColumnWidth = {"1x", 80};

% Volume viewer in left column
viewer = viewer3d(gl);
viewer.Layout.Row = 1;
viewer.Layout.Column = 1;
title(viewer, "Colorbar with Volshow");

V = rand([64 64 64]);
vol = volshow(V, Parent=viewer, Colormap=parula(256));

% Invisible axes with colorbar in right column
ax = uiaxes(gl, Visible="off", HitTest="off", PickableParts="none");
ax.Layout.Row = 1;
ax.Layout.Column = 2;
ax.Toolbar.Visible = "off";

% Match colormap and data range to the Volume object
ax.Colormap = vol.Colormap;
ax.CLim = [min(vol.Data, [], "all"), max(vol.Data, [], "all")];
cb = colorbar(ax, Units="normalized");

Linking Multiple Viewers

Use linkviewers to synchronize camera motion across multiple Viewers. When the user rotates or zooms one Viewer, all linked Viewers update to match. Pass "off" to unlink.

viewer1 = viewer3d();
viewer2 = viewer3d();
title(viewer1, "Original");
title(viewer2, "Segmentation");

volshow(V, Parent=viewer1);
volshow(V, Parent=viewer2, OverlayData=mask);

linkviewers([viewer1, viewer2]);

Conventions

• Always: Pass the Viewer as the first positional argument to images.ui.graphics.Surface(viewer, ...) — do NOT use Parent=viewer as a name-value argument
• Always: Reuse Volume objects by updating obj.Data — never recreate the volume each frame
• Always: Use waitfor(viewer, "Busy", false) to synchronize after setting Data when timing matters (screenshots, frame capture)
• Always: Use getframe(viewer) not getframe(gcf) for screenshots — the Viewer handles async completion
• Always: When the user has Medical Imaging Toolbox, use volshow(medVol) on a medicalVolume object — this auto-sets Transformation and SpatialUnits
• Never: Call clear(viewer) to reset the scene — reuse existing objects instead
• Never: Use isosurface + patch for mesh display when Image Processing Toolbox is available
• Prefer: OverlayData property for masks/segmentations over blending into Data or adding a second volume
• Prefer: Updating Transformation over re-setting Data when only position/size changes

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