Houdini 18.0 Executing Tasks

PDG Tutorial 2 Image Manipulation

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About this tutorial

There are many different ways that you can use PDG to manipulate and share the frames from your projects or productions.

In this tutorial you will learn how to import external media, extract and compress image files, filter frames, convert images, arrange your frames into image montages, and turn your frames into videos.

Each part of this tutorial will step through a different way that you can manipulate images with PDG.

Tip

To learn more about about TOPs & PDG, see Intro to TOPs.

Prerequisites

  • Basic understanding of TOP network set-up.

  • Some experience with the PDG workflow.

Tip

You can learn the basics of PDG by stepping through the Intro to PDG Part 1 - FX Workflow beginner tutorial.

What you will learn

  • Import/export media.

  • Unpack/generate image archive files.

  • Convert media.

  • Generate various kinds of image and video output.

Before you begin

Install ImageMagick

In parts one and two of this tutorial you will learn how to manipulate a series of images with PDG. To do this, you will use the ImageMagick TOP node.

To be able to use the ImageMagick node, you need to have the ImageMagick utility installed on your local system.

  1. Verify whether or not ImageMagick is installed on your system by doing the following:

    Mac

    In a terminal shell, type convert -version, and then press Enter.

    Windows

    In a Command Prompt, type imagemagick, and then press Enter.

    Linux

    In a command shell, type convert -version, and then press Enter.

    If anything but an error is returned, then ImageMagick is installed on your system and you can move on to step 3.

  2. If ImageMagick is not currently installed on your system, then you can download its installer from here.

    • Install ImageMagick.

  3. (Windows only) Once you are sure that ImageMagick is now installed on your system, verify that ImageMagick is in your system’s path.

    Windows

    1. Open the Edit the system environment variables control panel.

    2. In the System Properties window, click Environment Variables.

    3. In the Environment Variables window, select System variables > Path and then click Edit.

    4. In the Edit environment variable window, scroll through the list and locate the install directory for ImageMagick.

      If ImageMagick is missing from the list, then click Add, type or paste the path to your local ImageMagick install folder, and then click OK.

Install FFmpeg

In part three of this tutorial you will learn how to assemble a series of image files into a movie. To do this, you will use the FFmpeg Encode Video TOP node.

To be able to use the FFmpeg Encode Video node, you need to have the FFmpeg utility installed on your local system.

  1. Verify whether or not FFmpeg is installed on your system by doing the following:

    Mac

    In a terminal shell, type ffmpeg, and then press Enter.

    Windows

    In a Command Prompt, type ffmpeg, and then press Enter.

    Linux

    In a command shell, type ffmpeg, and then press Enter.

    If anything but an error is returned, then FFmpeg is installed on your system and you can move on to step 3.

  2. If FFmpeg is not currently installed on your system, then you can download its installer from here.

    • Install FFmpeg.

  3. (Windows only) Once you are sure that FFmpeg is installed on your system, verify that FFmpeg is in your system’s path.

    Windows

    1. Open the Edit the system environment variables control panel.

    2. In the System Properties window, click Environment Variables.

    3. In the Environment Variables window, select System variables > Path and then click Edit.

    4. In the Edit environment variable window, scroll through the list and locate the install directory for FFmpeg.

      If FFmpeg is missing from the list, then click Add, type or paste the path to your local FFmpeg install folder, and then click OK.

Copy over the tutorial image archives

Before you begin, please copy over the image archive (.zip) files that you will be working with in this tutorial:

  1. Open a file browser window and then navigate to your Houdini install directory.

  2. In the install directory, navigate to the $HH\pdg\examples\top_imagemanipulation folder.

  3. In the \top_imagemanipulation folder, copy the brimstone_images_compressed.zip and stock_pictures_compressed.zip files.

  4. Navigate to your PDG working directory and then create a new folder named \PDG_TUTORIAL_FILES.

  5. In the \PDG_TUTORIAL_FILES folder, paste the .zip files.


BEGIN

Initial Step - Pull in archive files and extract their images

In the initial step of this tutorial you will learn the image manipulation workflow for importing external media into a TOP network and extracting the contents from archive files. You will use a File Pattern TOP node to import external image archives and a File Decompress TOP node to unpack the archives so that you can use the individual images in each branch of your TOP network.

In parts 1, 2, and 3 of this tutorial, you will be creating three different network branches for three different image manipulation workflows.

  1. Run Houdini and start a new session.

  2. Save your new scene.

    • Name your scene file imagemaniptutorial.hip.

    • Save your .hip to the \PDG_TUTORIAL_FILES folder directory.

    This will be your working project file for the rest of the tutorial.

  3. In the Network Editor, navigate to the Tasks context and then dive into the topnet1 network.

  4. Create a File Pattern node and rename it to import_archives.

    In the TOPs ⇥ Tab menu, you can find File Pattern in the Files category.

    This node will import all the external .zip image archive files located in your $HIP directory.

  5. Select the import_archives node and then configure the following parameters:

    • In the Operation section, click in the Pattern parameter field and then type the following:

      $HIP/*.zip

      This will determine where on your system the node will look for the files and what file pattern (for example, like which file type) it should match.

      $HIP/ tells the node to look in your TOP network’s default working directory (as specified on the Scheduler node) for the image archive files, and the *.zip wild card tells the node to find and return all ZIP archive files.

      Tip

      To learn more about pattern wild cards, see Patterns.

    • In the Work Item section, make sure that the Split Files into Separate Items parameter is turned on.

      This tells the node to create separate work items for each matched file and store the filename data of each file in the node’s attributes.

    • Leave all the other parameters set to their default values.

  6. Cook the import_archives node.

    Two work items appear on the import_archives node and cook. One task represents the brimstone_images_compressed.zip archive file and the other task represents the stock_pictures_compressed.zip archive file.

  7. -click on the import_archives node and look at its node info.

    Notice the Outputs that are listed. The node was able to identify and import both these image archive files because you specified a wild card file pattern in the node’s Pattern parameter field.

  8. Create a File Decompress node and rename it to extract_images.

    In the TOPs ⇥ Tab menu, you can find File Decompress in the Files category.

    This node will extract the images from the archive files the import_archives node imported and then save them to disk.

  9. Select the extract_images node and then configure the following parameters:

    • In the Output section, click in the Output Folder parameter field and then type the following:

      $HIP/inputs/

      This tells the node to save the extracted image files to a new folder named /inputs in your working directory.

    • Leave all the other parameters set to their default values.

  10. Connect the input of the extract_images node to the output of the import_archives File Pattern node.

    These nodes now form the first part of your image manipulation TOP network.

  11. Cook the extract_images node.

    Two work items appear on the extract_images node and cook. One task represents the Brimstone image series and the other task represents the Stock Pictures image series.

    Note

    Notice the purple icon next to the extract_images node in the Network Editor.

    This icon indicates that the node is dynamic.

    In TOPs, there are two types of nodes: static and dynamic. Static nodes can generate their work items without any inputs as they are not dependent on any upstream data. Dynamic nodes on the other hand require information from their inputs upstream to generate their work items. That is why dynamic nodes can only generate work items once they are cooking.

    To learn more about about static and dynamic TOP nodes and their significance in a TOP network, see Static vs. Dynamic.


    The import_archives node imports the external ZIP archive files, and the extracted_images node then extracts the images from those archives files and saves them to disk.

  12. Look at the image files you extracted.

    In a file browser window, navigate to $HIP/inputs/ and inspect the images files.

    Result: Extracted Brimstone image series
    Result: Extracted Stock Pictures image series
  13. Save your tutorial scene.


Now that all the image files you will be working with are accessible, you can now manipulate them using the workflows outlined in the following parts of the tutorial.

Part 1 - Convert images and then bundle them in archive files

In part one of this tutorial you will learn the image manipulation workflow for converting images into different file formats and then compressing them into image archives. You will use an ImageMagick TOP node to convert the image files you unpacked in the initial step and a File Compress TOP node to bundle the converted images into new .zip archive files.

This process is helpful in situations where one part of your pipeline uses one image file format for frames, and another part of your pipeline uses a different image file format.

  1. Create an ImageMagick node, rename it to convert_images, and then connect its input to the output of the extract_images File Decompress node.

    In the TOPs ⇥ Tab menu, you can find ImageMagick in the Images category.

    This node will convert all the .jpg image files you extracted from the image archives to .png image files.

  2. Select the convert_images node and then configure the following parameters:

    • In the Operation parameter drop-down menu, select Convert.

      This tells the node to use the convert operation on the input images.

    • In the Operation section:

      • Set the Image Quality Percentage parameter to 100.

        This tells the node how much compression to use on the images it will convert and then output. The parameter value of 100 specifies no compression (full quality). Values less than 100 specify a percentage of compression and a reduction in quality. For example, a parameter value of 80 would compress the converted images by 20%.

      • In the Convert section, click in the Output Filename parameter field and then type the following:

        $HIP/images/{inputfilename}.png

        The {inputfilename} internal variable tells the node to name each .png image the same name as their original .jpg images.

      • Leave all the other parameters at their default values.

  3. Create a File Compress node, rename it to export_archives, and then connect its input to the output of the convert_images ImageMagick node.

    In the TOPs ⇥ Tab menu, you can find File Compress in the Files category.

    This node will bundle the .png images into new .zip archive files.

  4. Select the export_archives node and then configure the following parameters:

    • In the Ouput section:

      • In the Compress Method parameter drop-down menu, select ZIP.

        This tells the node to save out the new image archives as ZIP files.

      • In the Output section, click in the Output File field and then type the following:

        $HIP/archives/newarchive.`@pdg_index`.zip

        $HIP/archives tells the node to save the new archive files to a new folder named /archives in your working directory, and newarchivetells the node to prefix each archive file’s name with newarchive.

      • Leave all the other parameters at their default values.

  5. Cook the export_archives node.

    Two work items appear on the convert_images node representing the Brimstone images and Stock Pictures series of images and then cook.

    Two work items appear on the export_archives representing each of the new image archives and then cook.

    The convert_images node converts all the .jpg image files as .png image files and saves them to disk.

    The export_archives node then compresses the Brimstone images and Stock Pictures series of .png images into two new .zip archive files and saves them to disk.

  6. Look at the PNG images and ZIP archive files you created.

    • In a file browser window, navigate to $HIP/images/ and look at the converted images files.

      Notice that each of the converted images are named after their original filenames. This is because you used the {inputfilename} internal variable in the convert_images node’s Output Filename parameter field.

      Result: Converted Brimstone image series
      Result: Converted Stock Pictures image series
    • Navigate to $HIP/archives/ and inspect the new ZIP archive files.

      Result: New ZIP archive files
  7. Save your tutorial scene.


You can now easily share or distribute the converted images.

Part 2 - Assemble images into montages

In part two of this tutorial you will learn the image manipulation workflow for turning a series of images into a single image mosaic or montage. You will use an ImageMagick TOP node to assemble the image files you unpacked in the initial step into two image series montages.

This process is helpful in situations where you want to review and evaluate a series of frames side-by-side in a single composite image, like when comparing the wedged frame variations of a simulation.

  1. Create an ImageMagick node, rename it to make_montages, and then connect its input to the output of the extract_images File Decompress node.

    In the TOPs ⇥ Tab menu, you can find ImageMagick in the Images category.

    This node will take the image files you extracted from the image archives and arrange them into two montage (grid mosaic) images, one for each series of images.

  2. Select the make_montages node and then configure the following parameters:

    • Select the Node tab.

      • In the Operation parameter drop-down menu, select Montage.

        This tells the node to use the montage operation on the input images.

      • Click in the Output Filename parameter field and then type the following:

        $HIP/montage/mosaic.`@pdg_index`.png

        $HIP/montage tells the node to save the montage image files to a new folder named /montage in your working directory, and mosaic tells and the node to prefix each montage file’s name with mosaic.

    • Leave all the other parameters at their default values.

  3. Cook the make_montages node.

    Two work items appear on the node representing the Brimstone image series and the Stock Picture image series and then cook.

    The node assembles all the Brimstone images into one montage, all the Stock Picture images into another montage, and then saves both images to disk.

  4. Look at the montage images you created.

    In a file browser window, navigate to $HIP/montage/ and inspect the montage image files.

    Result: Montage of the Brimstone image series
    Result: Montage of the Stock Pictures image series
  5. Save your tutorial scene.


You can now view and compare all the images in the Brimstone and Stock Picture image series as two individual montage images.

Part 3 - Assemble images into a video

In part three of this tutorial you will learn the image manipulation workflow for turning a series of images into a video. You will use a Filter by Expression TOP node to remove the Stock Picture images from the inputs and an FFmpeg Encode Video TOP node to turn the remaining Brimstone image series into a movie.

This process is helpful in situations where you want to review or distribute your frames as a video.

  1. Create a Filter by Expression node, rename it to filter_images, and then connect its input to the output of the extract_images File Decompress node.

    In the TOPs ⇥ Tab menu, you can find Filter by Expression in the Data category.

    This node will use a custom expression to filter out any unwanted inputs.

  2. Select the filter_images node and then configure the following parameters:

    • Click in the Filter Expression parameter field and then press ⌃ Ctrl + e to open the Edit Expression window.

    • In Edit Expression window, do the following:

      • Click in the multi-line field.

        Multi-line field in the Edit Expression window

      • Remove the 0 and then type the following Python expression:

        len(pdg.workItem().resultDataForTag('file/image')) < 10

        This tells the node to remove from the inputs any series of images that has less than 10 images. For this tutorial, that series of images is the Stock Picture image series since it is comprised of only four images.

    • Click Accept.

      The Filter Expression parameter field turns green. This indicates that the parameter now contains an expression and the parameter’s expression language is currently set to HScript.

    • Since the expression you typed is written in Python and the Filter Expression parameter is currently set to HScript, you need to change the parameter’s expression language.

      -click the Filter Expression parameter and then select Expression ▸ Change Language to Python from the context-sensitive menu that appears.

      The Filter Expression parameter field turns purple. This indicates that the parameter’s expression language is now set to Python.

    • Leave all the other parameters at their default values.

  3. Create an FFmpeg Encode Video node, rename it to make_movie, and then connect its input to the output of the filter_images Filter by Expression node.

    In the TOPs ⇥ Tab menu, you can find FFmpeg Encode Video in the Images category.

    This node will take all the input images and turn them into a movie.

  4. Select the make_movie node and then configure the following parameters:

    • In the Cache Mode parameter drop-down menu, select Write Files.

      This tells the node to always work on the node’s work item and never use any existing cook result files from disk.

    • In the __Output__section, click in the Output File Path parameter field and then type the following:

      $HIP/movie/brimstonevideo.mp4

      $HIP/movie tells the node to save the video file to a new folder named /movie in your working directory, and .mp4 tells the node to save out the movie as an MP4 format video file.

    • Leave all the other parameters at their default values.

  5. Cook the make_movie node.

    One work item appears on the filter_images node representing the Brimstone series of images and then cooks.

    One work item appears on the make_movie node representing the video and then cooks.

    The filter_images node filters out the Stock Picture image series from the inputs.

    The make_movie node then assembles all the Brimstone images into an MP4 video file and saves it to disk.

  6. Examine the work item that is generated by the make_movie node.

    • Click the work item dot on the make_movie node.

      Notice the line that appears between the work item on the make_movie node and its associated work items on upstream tasks in the network. These lines and their corresponding dot highlights indicate the connections between the work items.

    • Click the first work item dot on the extract_images node, and then click the second work item dot on the same node.

      Notice how only one work item on the extract_images node is connected to the work item on the make_movie node. This is because the filter_images node has filtered out the Stock Picture image series from the video branch of the TOP network.

  7. Look at the movie you created.

    In a file browser window, navigate to $HIP/video/ and watch the MP4 video.

  8. Save your tutorial scene.


FINISH

Congratulations! You have completed the Image Manipulation PDG tutorial.

If you would like to see what your final TOPs network should look like, see the top_imagemanipulation.hip example file located in your Houdini example file directory ($HH\pdg\examples\top_imagemanipulation).

To continue learning about PDG workflows, you can step through the other beginner tutorials in this Houdini docs series or visit the Pipeline|PDG Learning Path on our website.

Executing Tasks

Basics

Beginner Tutorials

Next steps

Reference

  • All TOPs nodes

    TOP nodes define a workflow where data is fed into the network, turned into "work items" and manipulated by different nodes. Many nodes represent external processes that can be run on the local machine or a server farm.

  • Processor Node Callbacks

    Processor nodes generate work items that can be executed by a scheduler

  • Partitioner Node Callbacks

    Partitioner nodes group multiple upstream work items into single partitions.

  • Scheduler Node Callbacks

    Scheduler nodes execute work items

  • Custom File Tags and Cache Handlers

    PDG uses file tags to determine the type of an output file.

  • Python API

    The classes and functions in the Python pdg package for working with dependency graphs.