image variable attributes

• image-max - An string ``pointer'' attribute containing the variable name that stores the real value maximum for the image. In most cases the variable has the same name as the attribute.

• image-min - Like image-max, but points to the image-min variable for the image.

• complete - A boolean attribute (with values ``true_'' or ``false'') that indicates whether the variable has been written in its entirety. This can be used to detect program failure when writing out images as they are processed : complete is set to false at the beginning and set to true_ when all data has been processed and written to the file.