allele balance gatk

Hi,

I am trying to calculate allele balance for both the heterozygous (.40 to .60 ) and homozygous base through vcf file.
plz let me know how to achieve it through gatk.

I tried using FilterVCF(picard) command as follows

–I inputFile.vcf –MIN_AB -O outputfile.

I would really appreciate any help.

Regards,
Sabeen