The mask or "validity mask" segment within an image file informs which pixels in the image are valid. There are several applications that use this facility or concept.
The data model with the "validity mask" segment is shown below.
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We will illustrate the use of it with an ultrasound image. Shown below is the ultasound image and we wish to compute the statistics of it. Note that there is a "black" area that contains no valid information.
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Computing statistics on the image will include the entire "black" area.
Object Dimension: w=250 h=200 d=1 t=1 e=1 Mean: 63.2069 Variance: 2132.67 Std Dev: 46.1808 RMS: 78.2799 Total Contributing Points: 50000
If we incorporate a validity mask then the statistics computed on the image will not include the "black" area, i.e., only the unmasked data will be used for the computation. Shown below are the validity mask and the image with the validity mask segment.
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a) | b) |
The new statistics are shown below.
Object Dimension: w=250 h=200 d=1 t=1 e=1 Mean: 77.2634 Variance: 2384.87 Std Dev: 48.8351 RMS: 91.4026 Total Contributing Points: 33816
Below, the histogram of the original image and the histogram of the data of interest.
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a) | b) |