Hi Aberna,
I understand that you want to calculate the energy stored in DCT coefficients. The energy compaction property of DCT tells that you can reconstruct a signal from only a fraction of its DCT coefficients.
You can calculate the energy stored in DCT coefficients by applying 'norm' function to the DCT coefficients matrix. For more information please refer the example Energy Stored in DCT Coefficients.
I hope this helps.
