The Cloud Masking Settings window allows you to experiment with different cloud masking threshold values and immediately visualize the effects of the changes. As you change the values in each field, the Preview window displays the effect that the specified value will have on the image. The cloud mask that initially appears in the preview is calculated using default values and is displayed with 50% transparency, allowing you to see how accurately the mask matches the clouds.
The preview window displays the image at a 1:1 resolution; you can change the position of the window in the Overview pane to preview a different area of the image.
To specify cloud masking threshold values:
The Cloud Masking Settings window opens.
The Seed TOA value represents the brightest pixels on clouds. This value determines whether a cloud is included or excluded from the cloud mask. If a cloud has at least one pixel above this value, it is incuded in the mask. If all pixels in a cloud are below this value, the cloud is excluded from the cloud mask. If urban or other bright features are being misclassified as clouds, try increasing this value. If the mask is missing most of the clouds, try decreasing this value.
The Lowest TOA value represents the lowest value of all pixels in a cloud. If some portion of the cloud is being excluded from the mask, try decreasing this value. If clouds extend to urban features or other bright features, try increasing this value.
The Maximum dilation value represents the growing distance (in pixels) of each cloud. This distance does not consider the pixel values.
The specified cloud masking threshold values are automatically adjusted in the Cloud Masking fields.
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