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The compositing viewer pane, IPR viewer pane, and MPlay application all share the same basic image viewing interface.
The image view and graph view can display up to 16 COPs at a time (in a 4×4 viewport layout). The timeline view can display any number of COPs.
Tip
The IPR viewer pane cannot show multiple viewports at once. Otherwise, it uses the same image viewing interface. See how to use the IPR pane for information on controls unique to the IPR pane.
Mouse shortcuts ¶
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MMB |
Pan. |
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RMB |
Zoom. |
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⌃ Ctrl + RMB |
Box zoom. |
| mouse_wheel | Zoom. |
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⇧ Shift + LMB |
Select a region (click outside an image to deselect). |
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⇧ Shift + RMB |
Cancel region, show the entire image. |
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RMB |
Viewer menu. |
Work with images in the image viewer ¶
| To... | Do this |
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Choose the viewport layout (for Image and Graph views) |
On a compositing viewer’s main toolbar, use the Layout menu to choose the number of columns and rows of viewports (for example, “2×2”). If there are not enough sources to fill the viewports, Houdini will not show some rows or columns. To show all viewports regardless of whether they are blank or not, turn off the “Hide blank viewports” option at the bottom of the layout pop-up menu. |
Maximize a viewport |
Move the mouse over the viewport and press T. When a viewport is maximized, other viewports appear as tabs along the bottom of the viewer. |
Display the output of a compositing node (compositing viewer) |
Turn on the node’s display flag. Shift-click the flag to turn it on without turning off the display flags of other nodes. |
View different planes |
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View the full range of an HDR image |
Click the Adapt to pixel range button on the control toolbar or press ⇧ Shift + R. You can then use the color controls to fine tune the range you want to view. |
Work on a lower-resolution proxy image for better speed and memory usage |
In the main toolbar , change the Proxy Resolution menu from Full to the resolution reduction you want (1/2, 1/4, etc). This affects all image sequences. |
Only update a sub-region of the image |
Shift-drag a box around the region you want to focus on. Shift-click to clear the box and go back to updating the entire image. To home to the selected sub-region instead of the entire image, press G (Home selected centered at 100%) or ⇧ Shift + G (Home selected to fit viewport). |
Perform color correction of the viewer image |
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Set the background image of the viewer |
Tip Use a background image in the viewer to help you judge opacity.
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icon in the control bar From the menu. Choose Load LUT and select the LUT through the file browser.Analyze image problems in an image viewer ¶
The image viewer has several ways to debug common image problems, such as quantization and clipping.
View narrow color ranges ¶
You may want to see more detail in an area of the image, such as the shadows or highlights.
In the control toolbar, press the circular arrow button beside the Brightness/Contrast controls. This will switch to the alternate Black/White point controls.
For shadows, leave black at 0 and change white to a lower number, like 0.1 or 0.2. You should be able to view the shadow gradients in much more detail. All colors above the White point will appear white.
For highlights, leave white at 1 and change the black point to 0.9 or so.
For HDR images, you may need to set black and white points higher than 1. The easiest way to check the range is to click the Adapt Pixel Range button on the far right of the control toolbar. This will expand the black/white points to the min and max values in the image. From there, you can narrow down a range of color with the black/white point controls.
Inspect individual pixel values ¶
Right click in the viewer and turn on “Inspect”, or press I to enable the floating inspection box. As you move the pointer over the view, the box displays detailed information about what’s under the cursor.
In the image view, the box displays pixel location and values. In the timeline view, it displays information about the sequence, frame, and filename. In the graph view, it displays information about the X/Y position under the cursor.
Val
Pixel values in 0-1 form.
Raw
Raw pixel values, as they are stored (0-255 for 8 bit values, 0-65535 for 16 bit values, and so on).
HSL
Hue, saturation, and luminance of the pixel.
Pix
Pixel coordinates of the mouse pointer.
uv
UV (0-1) coordinates of the mouse pointer.
LUT
Only displayed if the Inspect LUT option on the Correction tab of the display options window is on. Shows a reverse mapping of the value through the LUT. This is useful for Cineon LUTs, to see the original Cineon numbers.
Histograms ¶
Use the image viewer’s graph view to see histograms of pixel values.
Compare images in the image viewer ¶
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Show the Difference toolbar if it’s collapsed. Right-click in the image view and turn on Diff in the context menu.
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Click the button menu at the left end of the toolbar to turn comparison on or off, or press ⌃ Ctrl + D.
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Right-click or press and hold on the button menu to choose the comparison method and source.
Link and unlink viewports ¶
When viewports are linked (on by default), changing a display option will affect all viewports. Linked viewports are labeled in Yellow. Unlinked viewports are labeled in white.
To link or unlink a viewport, move the mouse over the viewport and press V. You can also use the Apply Changes to All Views button in the main toolbar.
Options affected by linking are:
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Plane selector
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Display options (show guides, handles, previews, transparency, etc).
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Zoom buttons
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Color Correction controls (Component, Bright, Contrast, Gamma, LUT)
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Graph type
You can also link the viewing areas of viewports (off by default). Panning or zooming in one viewport will affect all viewports, so they show the same area. Press S, or click Link Scrolling to all Views at the right end of the main toolbar.
Image viewer toolbars ¶
Main toolbar ¶
Zooms in/out one level (2x).
Zooms the image to 100%. Hold ⇧ Shift and click to zoom to fit.
When on, automatically fits the image to the viewport. If Exact Pixel Size is also on, this will ensure the image is always centered at actual size (no zooming). This is automatically turned off if you pan across the image.
Show nodes with 
display flags on, along
with their state information and manipulators.
Show nodes with display flags on, but with the selected node’s manipulator (if the selected node is upstream from the node with the display flag).
This lets you work with the manipulator of the current node while viewing the end result (the node with the display flag).
Show the selected node, along with its state information and manipulators.
Maximizes the current viewport to fill the entire viewing area, hiding any other viewports. Click again to restore the viewport’s original size and position.
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When on, changing various controls, like the color correction and component controls, or the display item toggles, will affect all viewports. If off, only the current viewport is affected by these controls.
When on, zooming or panning in one viewport will zoom and pan all viewports.
View toolbar ¶
Exact Pixel Size
Always shows the image at actual size (100% scale), regardless of viewport size. This is automatically turned off if you manually zoom.
Clear Selection
Deselects any portion of the image has been selected (by RMB dragging).
Save Image
Lets you save the current viewport’s current frame to a file.
Fit Viewport to Image (MPlay only)
Shrinks or enlarges the MPlay window to fit the image. If more than one viewport is shown, resizes all viewports to the size of the largest viewport.
Display toolbar ¶
(Houdini Only)
Open the Display Options window. Click again to hide the window.
(Houdini Only)
Turn this option off to disable updates of the viewport (the viewport will show black). Use this to speed up complex operations.
Displays information in the top-left corner of the Viewport.
(Houdini only)
Displays all handles.
Shows gamuts and image border outline.
Shows a small preview of the entire image in the bottom-left corner. In MPlay, you can click LMB in this preview to pan to that spot, and drag MMB to select the viewing region.
Displays rulers on the edges of the viewer to let you judge sizes and distances.
When on, shows alpha transparency of the image. Most useful when used in conjunction with a background image.
When on, shows an image behind the current frame. Only visible if Transparency is on. Set the background image on the Background tab of the display options window.
Maintains the original pixel aspect ratio when zooming.
Toggles the Magnify window, which shows the area under the mouse cursor zoomed 10× with inspection and HSV info.
Correction toolbar ¶
The Correction toolbar contains image component and color controls.
These five buttons control which color plane(s) to show. The first icon shows all the planes (Red, Green, Blue, Alpha/Component 4). The next four turn the individual planes on or off.
The Alpha/Component 4 button will show the fourth component plane if one exists, otherwise it shows the alpha channel.
The default hotkeys for these buttons are ~, 1, 2, 3, and 4.
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menu button
Switches between Brightness/Contrast controls and Black/White Points.
Press R to reset all color correction controls to their default values.
Click the brightness button to reset the brightness to 1.
Enter a value in the number field for the brightness, or click MMB in the field to show a slider.
The field turns yellow when brightness is not 1.
Click the contrast button to reset the contrast to 1.
Enter a value in the number field for the contrast, or click MMB in the field to show a slider.
The field turns yellow when contrast is not 1.
This value is added to all pixels, effectively shifting the brightness of the entire image up or down. This can be useful for looking through intensity “slices” of the image.
The black point of the image, normally 0. This is applied after any image-specific white and black points, so 0 is always black and 1 is always white, regardless of the image data format.
The white point of the image, normally 1. This is applied after any image-specific white and black points, so 0 is always black and 1 is always white, regardless of the image data format.
Click the gamma button to reset the contrast to the default set in the display options window .
Enter a value in the number field for the gamma, or click MMB in the field to show a slider.
The field turns yellow when gamma is not at the default gamma setting.
Adjusts the black and white points to fit the minimum and maximum pixel values of the current image.
Difference toolbar ¶
The difference toolbar (⌃ Ctrl + D) lets you compare sequences or frames.
Blend factor
Controls how much of each image to show. Has different effects based on the comparison mode.
Image view ¶
In the main toolbar, click the 
View Image mode button.
The Image viewer can display 8, 16 and 32 bit integer images, floating point images, and deep rasters. You can view multiple sequences simultaneously and compare them. The Image Viewer and the standalone MPlay , are very similar. Most of the functions are identical.
The top two bars are only seen in Houdini - the top bar is the State Controller, and the bar directly underneath it is the Toolbox (currently showing the File COP toolbox). The next bar underneath the toolbox is the main image control bar, which contains most of the global functions to all image modes. The bar underneath that is the Diff bar, used when comparing two images together.
Along the left side are the View Controls, which contains the size adapt, zoom, home and PI buttons. Along the right side is the Display Options, which contains the display item toggle buttons (guides, transparency, background image, etc.).
Along the bottom is the Image Controls, which contains the Component and Color correction controls. Above it is the Inspection bar, which shows information on the pixel under the mouse cursor.
Timeline view ¶
In the main toolbar, click the 
Timeline mode button.
Timeline view shows the sequences in a time graph for timing analysis.
The timeline only has 1 viewport, which displays all the sequences vertically on the timing graph. Single Images always appear in the middle of the graph, as they exist everywhere.
Animated sequences have a start and an end.
The current frame range is shown as a black background. Anything outside that range is grey. The sequence strips themselves have squares in them, representing individual frames. Blue frames are ones that exist (or aren’t corrupt). Black frames indicate missing frames. Bright blue frames indicate that a preview is visible at that frame.
You can preview images on the strips. Houdini shows very small thumbnails (less than 100×100) at regular intervals on the strip. Press ⌃ Ctrl + P to show the previews. Set the frequency of the previews in the control toolbar (Preview Every)
Main toolbar ¶
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The Resolution and Layout menus are not on the toolbar because they do not apply to the timeline view.
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the COP Filter button lets you choose which COP nodes to show (Displayed, Time Sensitive, or All).
Adapt toolbar ¶
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When Horizontal Adapt is on, the viewport automatically pans and zooms to show all sequence ranges.
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When Vertical Adapt is on, the viewport automatically pans and zooms to show all sequences.
Control toolbar ¶
Preview
Sets the rate at which previews appear in the sequence. Turn previews on in the display toolbar to see the previews.
Display toolbar ¶
Show preview
Shows preview thumbnails on the timelines. Set the interval between previews with the Preview control on the Control toolbar.
Show frame boxes
Shows/hides boxes around the time a frame is visible.
Show extend regions
Shows regions controlled by Cycle, Mirror, Hold and Hold for N Frames conditions on the timeline.
Show timebar
Shows/hides a vertical blue line at the current time.
Graph view ¶
In the main toolbar, click the 
Graph mode button.
Graph view displays a variety of graphs and histograms based on the pixel values of the image. It is useful for data analysis of images (quantization, dynamic range, errors, etc.).
The graph view supports up to 16 viewports.
By default, the histograms don’t adapt the entire range of the graph; they clip off the top 2% of the maximum pixel occurrences. This prevents the background color (which will probably be the most prevalent color) from causing the graph to adapt to a single spike. You can toggle this off by pressing ⇧ Shift + S (or by clicking “Ignore Graph Spikes during Adapt” at the bottom of the View toolbar). This only applies to the first 4 histograms, not the graphs.
Control toolbar ¶
The control bar contains the same component selectors as the Image view. There is also a menu to choose graph type:
Pixel Histogram
Frequencies of occurrence of pixel values in the image as a bar graph.
Hue Histogram
Frequencies of occurrence of hues in the image as a bar graph (you must have a vector plane of 3 or 4 elements).
Saturation Histogram
Frequencies of occurrence of saturation levels in the image as a bar graph.
Value Histogram
Frequencies of occurrence of pixel value levels in the image as a bar graph.
Pixel/Hue/Saturation/Value Vs U/V
These 8 graphs show the pixel value, hue, saturation or value of pixel rows or columns in the image. The values are plotted as individual points. Dense regions of the graph will appear more white than blue.
Hue Vs Saturation
Saturation range of the different hues in the image. Dense regions of the graph (ie, many occurrences of the same hue-saturation pair) will appear whiter than the normal hue.
Hue Vs Value
Value range of different hues in the image. Dense regions of the graph (ie, many occurrences of the same hue-saturation pair) will appear whiter than the normal hue.
Adapt toolbar ¶
Horizontal Adapt
The viewport automatically pans and zooms to show the full horizontal domain of the graph.
Vertical Adapt
The viewport automatically pans and zooms to show the full vertical range of the graph.
Ignore Spikes During Adapt
Ignores the top 2% of data points when calculating the full vertical range of values for Vertical Adapt. This keeps spikes in the data from affecting the vertical range.
Graph types ¶
Pixel Histogram
Shows the occurrence of pixel component values.
Hue Histogram
Shows the occurrence of the pixel hues.
Saturation Histogram
Shows the occurrence of pixel saturation.
Value Histogram
Shows the occurrence of pixel values (that is, level of brightness, as in hue, saturation, and value).
Color Curves
Shows the color transformation that the image is under. Only used in the COP viewer, for Blue Color correction nodes.
Pixel vs. U/V
Shows the pixel’s values mapped along the Y axis, and the horizontal/vertical position along the X.
Hue/Saturation/Value vs. U/V
Same as above, but for hue, saturation, or value.
Hue vs. Saturation
Plots each hue’s saturation, showing how saturated the various colors in the image are.
Hue vs. Value
Plots each hue’s value, showing how bright the various colors in the image are.