Image viewer interface - Houdini online help

Mouse shortcuts

	Zoom.
Ctrl +	Box zoom.
Mouse wheel	Zoom.
	Pan.
⇧ Shift +	Select a region (click outside an image to deselect).
⇧ Shift +	Cancel ⇧ Shift + region, show the entire image.
	Viewer menu.

Work with images in the image viewer

To...	Do this
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. 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 option at the bottom of the layout pop-up menu.
Maximize a viewport	Move the mouse over the viewport and press T . Press T again to restore the viewport’s original size and position. 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.
Choose the COPs to show in timeline view	Use the Show menu in main toolbar to show all nodes or show timing-related nodes.
Set the current viewport	Move the mouse over a viewport and press X . Some actions only affect the current viewport, such as File > Save Current Frame and File > Save Preview. See also linking and unlinking viewports .
View different planes	Use the controls on the control toolbar to switch between viewing full color, individual color channels, or alpha. Press ⇧ Shift + [ and ⇧ Shift + ] to cycle through the planes in the image.
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	Use the sliders on the control toolbar to adjust the color and gamma of the display. To use a look-up table , click the LUT icon in the control bar (a circled L). From the menu, choose Load LUT and select the LUT through the file browser.
Set the background image of the viewer	On the right toolbar, click the display options button to open the Display Options window. Use the controls on the Background tab to load a background image. Transparency will automatically be enabled, as will double buffering (to avoid flicker). Use a background image in the viewer to help you judge opacity. To turn off the background image, open the display bar and disable the 'Background Image' display icon (second from bottom), or open the display options again and remove the filename.

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

Pressing I to show the Inspect toolbar under the viewports. This is useful for analyzing bad pixels and edges.

Zoom into the image for more precise pixel analysis.

Histograms

Use the image viewer’s graph view to see histograms of pixel values.

Compare images in the image viewer

Open the Diff toolbar . Choose Pane > Toolbars and Controls > Diff Bar (in a viewer pane) or Settings > Diff (in MPlay ).
To choose the image/sequence to compare to, do any of the following:
Open the Compare menu (next to the down-arrow sequence menu) and choose a method for comparing the sequences:
To stop comparing, collapse or hide the Diff toolbar.

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.

Linked
Unlinked

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:

Plane selector
Display options (show guides, handles, previews, transparency, etc).
Zoom buttons
Color Correction controls (Component, Bright, Contrast, Gamma, LUT)
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 the main toolbar.

Image viewer toolbars

Main toolbar

Mode menu

Sets viewer to image , timeline , or graph mode.

Plane menu

Which image plane to display (Color, Alpha, Point, etc).

Zoom menu

Sets the zoom level, from 12.5% to 800%.

Layout menu

Sets the viewport layout, from 1×1 (1 viewport only) to 4×4.

Frame controls

These three buttons step move back and forward along the sequence.

Back/Forward 1 Frame	Moves back/forward exactly 1 frame, even if the sequence’s FPS does not match the playback FPS. If moving 1 frame would go outside the sequence, it wraps to the end/start.
Adapt Frame Range	Sets the global playback range to the sequence’s frame range in the current Viewport.

Zoom Viewport

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.

Link Viewports

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.

Link Viewports Scroll

When on, zooming or panning in one viewport will zoom and pan all viewports.

View toolbar

Zoom In/Out	Zooms in/out one level (2x).
Home	Zooms the image to 100%. Hold ⇧ Shift and click to zoom to fit.
Size Adapt	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.
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 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

Display Options (Houdini Only)	Open the Display Options window . Click again to hide the window.
Enable View (Houdini Only)	Turn this option off to disable updates of the viewport (the viewport will show black). Use this to speed up complex operations.
Show Labels	Displays information in the top-left corner of the Viewport.
Show Handles (Houdini only)	Displays all handles.
Show Guides	Shows gamuts and image border outline.
Show Preview	Shows a small preview of the entire image in the bottom-left corner. In MPlay, you can click in this preview to pan to that spot, and drag to select the viewing region.
Toggle Transparency	When on, shows alpha transparency of the image. Most useful when used in conjunction with a background image.
Toggle 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.
Magnify Window	Toggles the Magnify window, which shows the area under the mouse cursor zoomed 10x with inspection and HSV info.

Control toolbar

The Control bar contains image component and color controls.

Component Toggles	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 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 .
Image Modifier Switch	Click this button to switch between Brightness/Contrast controls and Black/White Points. Press R to reset all color correction controls to their default values.
Brightness	Click the brightness button to reset the brightness to 1. Enter a value in the number field for the brightness, or click in the field to show a slider. The button turns red when brightness is not 1.
Contrast	Click the contrast button to reset the contrast to 1. Enter a value in the number field for the contrast, or click in the field to show a slider. The button turns red when contrast is not 1.
Bright shift	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.
Black point	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.
White Point Reset & Value	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.
Gamma	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 in the field to show a slider. The button turns red when gamma is not 1.
Adapt to Full Pixel Range	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.

Compare to menu

Choose a COP source to compare the current frame to.

Comparison mode menu

The type of comparison to perform.

Subtract	Subtracts the compare-to image from the current image. This will potentially produce negative values (use the Adapt to Full Pixel Range button to view properly).
Split Horizontal/Vertical	Shows the current image and compare-to image side-by-side. Use the blend factor to control how much of each image to show. MPlay only: click the image to set the split point.
Blend	Blends the current and compared image together. Use the blend factor to control how much of each image to show (0 = only the current image, 1 = only the compare-to image, 0.5 = 50% of each, etc.).
Highlight Differences	Highlights any pixels in the current image that differ from the compared image by more than the threshold set with the Blend factor. The default threshold is 0, so all differences will be highlighted. The threshold is measured in normalized color space (1 unit is equal to the range from black to white).

Blend factor

Controls how much of each image to show. Has different effects based on the comparison mode.

Current frame menu

Choose the frame from the image sequence to compare, such as the current frame, next frame, or a specific frame.

Inspect toolbar

The inspect bar shows information based on what is under the mouse pointer. This information changes based on the viewer mode:

Image View	Pixel location and value.
Timeline View	Information on sequence under the cursor, plus the frame and filename information.
Graph View	Information on the X/Y position under the cursor.

Press I to open the inspection bar. Press M for a zoomed detail window plus the inspection information.

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.

Operation controls toolbar

The selector toolbox can be used to select inputs and optionally determine the planes to create.

The first half of the toolbox deals with input wiring, and is common between the Generator and Filter Selectors. The text prompt shows you the input label of the input you are currently wiring. The pull down menu allows you to select any COP in your current network. The next button completes the node creation and places the node in the current viewport if pressed. The “X” button removes the last wired input and allows you to re-wire it.

The second half of the toolbox is specific to the Generator Selector. If the toggle is off, none of the settings are applied to the created node - its defaults are used instead.

The first menu selects which type of plane to create. The next string field allows you to enter your own custom planes (For example foo{r,g,b}. See the online help for the Generator operators for more information). The next menu sets the compositing operation to perform if the generator is doing Quick Compositing. The last menu selects the data type for the plane.

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.

Follow mode

The viewer has three modes choices for which COP’s output to display, controlled by the small 3 button strip in the top right corner of the viewer:

Follow display (blue)

Show nodes with display flags on, along with their state information and manipulators.

Follow display/current (blue and green)

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).

Follow current (green)

Show the “current” node, along with its state information and manipulators.

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)