Auto-fix corrupt JPEGs (ultralytics#4548)

* Autofix corrupt JPEGs

This PR automatically re-saves corrupt JPEGs and trains with the resaved images. WARNING: this will overwrite the existing corrupt JPEGs in a dataset and replace them with correct JPEGs, though the filesize may increase and the image contents may not be exactly the same due to lossy JPEG compression schemes. Results may vary by JPEG decoder and hardware.

Current behavior is to exclude corrupt JPEGs from training with a warning to the user, but many users have been complaining about large parts of their dataset being excluded from training.

* Clarify re-save reason

utils/datasets.py

@@ -314,7 +314,7 @@ def __init__(self, sources='streams.txt', img_size=640, stride=32, auto=True):
         print('')  # newline
 
         # check for common shapes
-        s = np.stack([letterbox(x, self.img_size, stride=self.stride, auto=self.auto)[0].shape for x in self.imgs], 0)  # shapes
+        s = np.stack([letterbox(x, self.img_size, stride=self.stride, auto=self.auto)[0].shape for x in self.imgs])
         self.rect = np.unique(s, axis=0).shape[0] == 1  # rect inference if all shapes equal
         if not self.rect:
             print('WARNING: Different stream shapes detected. For optimal performance supply similarly-shaped streams.')
@@ -568,7 +568,7 @@ def __getitem__(self, index):
         if self.augment:
             # Albumentations
             img, labels = self.albumentations(img, labels)
-            nl = len(labels) # update after albumentations
+            nl = len(labels)  # update after albumentations
 
             # HSV color-space
             augment_hsv(img, hgain=hyp['hsv_h'], sgain=hyp['hsv_s'], vgain=hyp['hsv_v'])
@@ -861,7 +861,7 @@ def autosplit(path='../datasets/coco128/images', weights=(0.9, 0.1, 0.0), annota
 def verify_image_label(args):
     # Verify one image-label pair
     im_file, lb_file, prefix = args
-    nm, nf, ne, nc = 0, 0, 0, 0  # number missing, found, empty, corrupt
+    nm, nf, ne, nc, msg, segments = 0, 0, 0, 0, '', []  # number (missing, found, empty, corrupt), message, segments
     try:
         # verify images
         im = Image.open(im_file)
@@ -872,10 +872,11 @@ def verify_image_label(args):
         if im.format.lower() in ('jpg', 'jpeg'):
             with open(im_file, 'rb') as f:
                 f.seek(-2, 2)
-                assert f.read() == b'\xff\xd9', 'corrupted JPEG'
+                if f.read() != b'\xff\xd9':  # corrupt JPEG
+                    im.save(im_file, format='JPEG', subsampling=0, quality=100)  # re-save image
+                    msg = f'{prefix}WARNING: corrupt JPEG restored and saved {im_file}'
 
         # verify labels
-        segments = []  # instance segments
         if os.path.isfile(lb_file):
             nf = 1  # label found
             with open(lb_file, 'r') as f:
@@ -896,7 +897,7 @@ def verify_image_label(args):
         else:
             nm = 1  # label missing
             l = np.zeros((0, 5), dtype=np.float32)
-        return im_file, l, shape, segments, nm, nf, ne, nc, ''
+        return im_file, l, shape, segments, nm, nf, ne, nc, msg
     except Exception as e:
         nc = 1
         msg = f'{prefix}WARNING: Ignoring corrupted image and/or label {im_file}: {e}'