VOC数据集格式转化成COCO数据集格式
一、唠叨
     之前写过一篇关于coco数据集转化成VOC格式的博客COCO2VOC，最近读到CenterNet的官方代码，实现上则是将voc转化成coco数据格式，这样的操作我个人感觉很不习惯，也觉得有些奇葩，可能是每个人习惯不一样吧，我们知道有时候我们会采用labelImg标注数据，标注出来的格式就是voc，如果直接训练就可以用来训练是不是更加友好。

     为了不大规模修改原始训练代码（虽然自己修改了一个版本的voc数据集就能直接训练centernet 😊）,同时也看到网上很多大佬也做了将VOC数据格式转化成COCO用于其训练，这里我自己做一个精细一点的，作为笔记。

二、转化过程
   数据格式的转换实际是annotation标注文件的转化，voc的数据标注文件为以.xml结尾的文件，而且每张图片均有一个对应的同名标注文件；COCO则是将所有的标注信息写在一个json文件中。VOC数据集目录如下：

    在之前的coco2voc博客中做了详细的介绍，现在直接开始转化，目标就是将Annotations中的所有标注文件中的bbox标注信息转化为json文件，根据训练集和测试集，则主要转化为四个json文件，分别是test.json、train.json、val.json和trainval.json .这里我根据ImageSets中的train.txt val.txt trainval.txt生成后三个json文件，当然也可以直接从Annotations文件夹生成。

VOC2COCO.pyimport xml.etree.ElementTree as ET
import os
import jsoncoco = dict()
coco['images'] = []
coco['type'] = 'instances'
coco['annotations'] = []
coco['categories'] = []category_set = dict()
image_set = set()category_item_id = -1
image_id = 20180000000
annotation_id = 0def addCatItem(name):global category_item_idcategory_item = dict()category_item['supercategory'] = 'none'category_item_id += 1category_item['id'] = category_item_idcategory_item['name'] = namecoco['categories'].append(category_item)category_set[name] = category_item_idreturn category_item_iddef addImgItem(file_name, size):global image_idif file_name is None:raise Exception('Could not find filename tag in xml file.')if size['width'] is None:raise Exception('Could not find width tag in xml file.')if size['height'] is None:raise Exception('Could not find height tag in xml file.')image_id += 1image_item = dict()image_item['id'] = image_idimage_item['file_name'] = file_nameimage_item['width'] = size['width']image_item['height'] = size['height']coco['images'].append(image_item)image_set.add(file_name)return image_iddef addAnnoItem(object_name, image_id, category_id, bbox):global annotation_idannotation_item = dict()annotation_item['segmentation'] = []seg = []# bbox[] is x,y,w,h# left_topseg.append(bbox[0])seg.append(bbox[1])# left_bottomseg.append(bbox[0])seg.append(bbox[1] + bbox[3])# right_bottomseg.append(bbox[0] + bbox[2])seg.append(bbox[1] + bbox[3])# right_topseg.append(bbox[0] + bbox[2])seg.append(bbox[1])annotation_item['segmentation'].append(seg)annotation_item['area'] = bbox[2] * bbox[3]annotation_item['iscrowd'] = 0annotation_item['ignore'] = 0annotation_item['image_id'] = image_idannotation_item['bbox'] = bboxannotation_item['category_id'] = category_idannotation_id += 1annotation_item['id'] = annotation_idcoco['annotations'].append(annotation_item)def _read_image_ids(image_sets_file):ids = []with open(image_sets_file) as f:for line in f:ids.append(line.rstrip())return ids"""通过txt文件生成"""
#split ='train' 'va' 'trainval' 'test'
def parseXmlFiles_by_txt(data_dir,json_save_path,split='train'):print("hello")labelfile=split+".txt"image_sets_file = data_dir + "/ImageSets/Main/"+labelfileids=_read_image_ids(image_sets_file)for _id in ids:xml_file=data_dir + f"/Annotations/{_id}.xml"bndbox = dict()size = dict()current_image_id = Nonecurrent_category_id = Nonefile_name = Nonesize['width'] = Nonesize['height'] = Nonesize['depth'] = Nonetree = ET.parse(xml_file)root = tree.getroot()if root.tag != 'annotation':raise Exception('pascal voc xml root element should be annotation, rather than {}'.format(root.tag))# elem is <folder>, <filename>, <size>, <object>for elem in root:current_parent = elem.tagcurrent_sub = Noneobject_name = Noneif elem.tag == 'folder':continueif elem.tag == 'filename':file_name = elem.textif file_name in category_set:raise Exception('file_name duplicated')# add img item only after parse <size> tagelif current_image_id is None and file_name is not None and size['width'] is not None:if file_name not in image_set:current_image_id = addImgItem(file_name, size)print('add image with {} and {}'.format(file_name, size))else:raise Exception('duplicated image: {}'.format(file_name))# subelem is <width>, <height>, <depth>, <name>, <bndbox>for subelem in elem:bndbox['xmin'] = Nonebndbox['xmax'] = Nonebndbox['ymin'] = Nonebndbox['ymax'] = Nonecurrent_sub = subelem.tagif current_parent == 'object' and subelem.tag == 'name':object_name = subelem.textif object_name not in category_set:current_category_id = addCatItem(object_name)else:current_category_id = category_set[object_name]elif current_parent == 'size':if size[subelem.tag] is not None:raise Exception('xml structure broken at size tag.')size[subelem.tag] = int(subelem.text)# option is <xmin>, <ymin>, <xmax>, <ymax>, when subelem is <bndbox>for option in subelem:if current_sub == 'bndbox':if bndbox[option.tag] is not None:raise Exception('xml structure corrupted at bndbox tag.')bndbox[option.tag] = int(option.text)# only after parse the <object> tagif bndbox['xmin'] is not None:if object_name is None:raise Exception('xml structure broken at bndbox tag')if current_image_id is None:raise Exception('xml structure broken at bndbox tag')if current_category_id is None:raise Exception('xml structure broken at bndbox tag')bbox = []# xbbox.append(bndbox['xmin'])# ybbox.append(bndbox['ymin'])# wbbox.append(bndbox['xmax'] - bndbox['xmin'])# hbbox.append(bndbox['ymax'] - bndbox['ymin'])print('add annotation with {},{},{},{}'.format(object_name, current_image_id, current_category_id,bbox))addAnnoItem(object_name, current_image_id, current_category_id, bbox)json.dump(coco, open(json_save_path, 'w'))"""直接从xml文件夹中生成"""
def parseXmlFiles(xml_path,json_save_path):for f in os.listdir(xml_path):if not f.endswith('.xml'):continuebndbox = dict()size = dict()current_image_id = Nonecurrent_category_id = Nonefile_name = Nonesize['width'] = Nonesize['height'] = Nonesize['depth'] = Nonexml_file = os.path.join(xml_path, f)print(xml_file)tree = ET.parse(xml_file)root = tree.getroot()if root.tag != 'annotation':raise Exception('pascal voc xml root element should be annotation, rather than {}'.format(root.tag))# elem is <folder>, <filename>, <size>, <object>for elem in root:current_parent = elem.tagcurrent_sub = Noneobject_name = Noneif elem.tag == 'folder':continueif elem.tag == 'filename':file_name = elem.textif file_name in category_set:raise Exception('file_name duplicated')# add img item only after parse <size> tagelif current_image_id is None and file_name is not None and size['width'] is not None:if file_name not in image_set:current_image_id = addImgItem(file_name, size)print('add image with {} and {}'.format(file_name, size))else:raise Exception('duplicated image: {}'.format(file_name))# subelem is <width>, <height>, <depth>, <name>, <bndbox>for subelem in elem:bndbox['xmin'] = Nonebndbox['xmax'] = Nonebndbox['ymin'] = Nonebndbox['ymax'] = Nonecurrent_sub = subelem.tagif current_parent == 'object' and subelem.tag == 'name':object_name = subelem.textif object_name not in category_set:current_category_id = addCatItem(object_name)else:current_category_id = category_set[object_name]elif current_parent == 'size':if size[subelem.tag] is not None:raise Exception('xml structure broken at size tag.')size[subelem.tag] = int(subelem.text)# option is <xmin>, <ymin>, <xmax>, <ymax>, when subelem is <bndbox>for option in subelem:if current_sub == 'bndbox':if bndbox[option.tag] is not None:raise Exception('xml structure corrupted at bndbox tag.')bndbox[option.tag] = int(option.text)# only after parse the <object> tagif bndbox['xmin'] is not None:if object_name is None:raise Exception('xml structure broken at bndbox tag')if current_image_id is None:raise Exception('xml structure broken at bndbox tag')if current_category_id is None:raise Exception('xml structure broken at bndbox tag')bbox = []# xbbox.append(bndbox['xmin'])# ybbox.append(bndbox['ymin'])# wbbox.append(bndbox['xmax'] - bndbox['xmin'])# hbbox.append(bndbox['ymax'] - bndbox['ymin'])print('add annotation with {},{},{},{}'.format(object_name, current_image_id, current_category_id,bbox))addAnnoItem(object_name, current_image_id, current_category_id, bbox)json.dump(coco, open(json_save_path, 'w'))if __name__ == '__main__':#通过txt文件生成# voc_data_dir="E:/VOCdevkit/VOC2007"# json_save_path="E:/VOCdevkit/voc2007trainval.json"# parseXmlFiles_by_txt(voc_data_dir,json_save_path,"trainval")#通过文件夹生成ann_path="E:/VOCdevkit/VOC2007/Annotations"json_save_path="E:/VOCdevkit/test.json"parseXmlFiles(ann_path,json_save_path)

 生成之后就是这样：

到此就结束了，提供两个关键函数，一个是通过txt，另一个使用过文件夹，然后就可以用于centernet训练了，或者也可以用于其他的算法数据准备。

任何程序错误，以及技术疑问或需要解答的，请添加