How Labeler Apps Store Exported Pixel Labels - MATLAB & Simulink (original) (raw)

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When you create and export pixel labels from the Image Labeler,Video Labeler, orGround Truth Labeler (Automated Driving Toolbox) (requires Automated Driving Toolbox™) app, two sets of data are saved.

The PNG files within the PixelLabelData folder are stored as a categorical matrix. The categorical matrices contain values assigned to categories. Categorical is a data type. A categorical matrix provides efficient storage and convenient manipulation of nonnumeric data, while also maintaining meaningful names for the values. These matrices are natural representations for semantic segmentation ground truth, where each pixel is one of a predefined category of labels.

Location of Pixel Label Data Folder

The ground truth object stores the folder path and name for the pixel label data folder. The LabelData property of the groundTruth object or ROILabelData property of thegroundTruthMultisignal object contains the information in the'PixelLabelData' column. If you change the location of the pixel data file, you must also update the related information in the ground truth object. You can use the changeFilePaths function to update the information.

View Exported Pixel Label Data

The labeler apps store the semantic segmentation ground truth as lossless PNG files, with a uint8 value representing each category. The app uses thecategorical function to associate theuint8 values to a category. To view your pixel data, you can either overlay the categories on images or create a datastore from the labeled images.

View Exported Pixel Label Data by Overlaying Categories on Images

Use the imread function with the categorical and labeloverlay functions. You cannot view the pixel data directly from the categorical matrix. See View Exported Pixel Label Data.

View Exported Pixel Label Data from Datastore of Labeled Images

Use the pixelLabelDatastore function to create a datastore from a set of labeled images. Use the read function to read the pixel label data. See Read and Display Pixel Label Data.

Examples

View Exported Pixel Label Data

Read image and corresponding pixel label data that was exported from a labeler app.

visiondatadir = fullfile(toolboxdir('vision'),'visiondata');

buildingImage = imread(fullfile(visiondatadir,'building','building1.JPG')); buildingLabels = imread(fullfile(visiondatadir,'buildingPixelLabels','Label_1.png'));

Define categories for each pixel value in buildingLabels.

labelIDs = [1,2,3,4]; labelcats = ["sky" "grass" "building" "sidewalk"];

Construct a categorical matrix using the image and the definitions.

buildingLabelCats = categorical(buildingLabels,labelIDs,labelcats);

Display the categories overlaid on the image.

figure imshow(labeloverlay(buildingImage,buildingLabelCats))

Figure contains an axes object. The hidden axes object contains an object of type image.

Read and Display Pixel Label Data

Overlay pixel label data on an image.

Set the location of the image and pixel label data.

dataDir = fullfile(toolboxdir('vision'),'visiondata'); imDir = fullfile(dataDir,'building'); pxDir = fullfile(dataDir,'buildingPixelLabels');

Create an image datastore.

imds = imageDatastore(imDir);

Create a pixel label datastore.

classNames = ["sky" "grass" "building" "sidewalk"]; pixelLabelID = [1 2 3 4]; pxds = pixelLabelDatastore(pxDir,classNames,pixelLabelID);

Read the image and pixel label data. read(pxds) returns a categorical matrix, C. The element C(i,j) in the matrix is the categorical label assigned to the pixel at the location l(i,j).

I = read(imds); C = read(pxds);

Display the label categories in C.

ans = 4×1 cell {'sky' } {'grass' } {'building'} {'sidewalk'}

Overlay and display the pixel label data onto the image.

B = labeloverlay(I,C{1}); figure imshow(B)

Figure contains an axes object. The hidden axes object contains an object of type image.

See Also

Apps

Objects

Functions

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