How to train with custom dataset?

I want to train with custom dataset, and I have some questions: (1) my custom dataset has two folders images and labels, where each label image is RGB image which uses different color for different object class. Should I organize this dataset in Pascal VOC format? (2) I need to adapt voc_unet.py for custom dataset, Pascal VOC uses ignore_label for object boundary, how to set ignore_label for my own custom dataset? (3) How to set crop_size_h, crop_size_w = 513, 513? My custom dataset has image dimension 512x512. Thanks!