Real-time feature extraction from video stream data for stream ...

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Real-time feature extraction from video stream data for stream ...

6.2. Image Feature Extraction with RapidMiner

First of all both frames are loaded as monochrome images using the Open Gray-scale

Image operator. Then the grayscale values of all pixels in both images have to be multiplied

with 0.5. Afterwards 128 is added to all pixel values in one of the images, and

last the two images get subtracted using the Image Combinator operator. An example

for the output of this process can be found in figure 2.5.

Global image statistics

So far I have only described operators that transform images. The next two paragraphs

now cope with the actual feature extraction.

The IMMI Extension offers an operator called Global Feature Extractor from a Single

Image to extract global statistics or histograms from images. Table 6.1 shows an overview

of all features that can be extracted by the Global Statistics-Operator.

The output of the operator is an ExampleSet containing values for all requested features.

I have applied this operator on the original image, the grayscale image, each color

channel, the reverse engineered difference image, the black and white image, and an image

resulting from the border detection separately. Further details are described in the

following section 6.2.2.

Histograms

Beside the Global Statistics-Operator, another interesting operator for extracting information

from an image is the Histogram-Operator. A color histogram represents the

distribution of colors in an image. After defining the number of bins, color ranges, which

cover the whole color space of the image, are derived automatically. Then each pixel

is sorted into the corresponding bin and afterwards the number of pixels in each bin is

counted. The relative count of pixels belonging to a bin then is the value for this bin. The

color histogram therefore can be seen as an statistical approximation of the continuous

distribution of color values for a frame.

Figure 6.6.: The RapidMiner process for reproducing the difference image of two frames.

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