PR: Make JPEG/PNG reading ops return images in CHW format (#2680)

* Make JPEG/PNG return images in CHW format

* Use int array

test/test_image.py

@@ -30,12 +30,14 @@ class ImageTester(unittest.TestCase):
     def test_read_jpeg(self):
         for img_path in get_images(IMAGE_ROOT, ".jpg"):
             img_pil = torch.load(img_path.replace('jpg', 'pth'))
+            img_pil = img_pil.permute(2, 0, 1)
             img_ljpeg = read_jpeg(img_path)
             self.assertTrue(img_ljpeg.equal(img_pil))
 
     def test_decode_jpeg(self):
         for img_path in get_images(IMAGE_ROOT, ".jpg"):
             img_pil = torch.load(img_path.replace('jpg', 'pth'))
+            img_pil = img_pil.permute(2, 0, 1)
             size = os.path.getsize(img_path)
             img_ljpeg = decode_jpeg(torch.from_file(img_path, dtype=torch.uint8, size=size))
             self.assertTrue(img_ljpeg.equal(img_pil))
@@ -68,12 +70,14 @@ class ImageTester(unittest.TestCase):
         # Check across .png
         for img_path in get_images(IMAGE_DIR, ".png"):
             img_pil = torch.from_numpy(np.array(Image.open(img_path)))
+            img_pil = img_pil.permute(2, 0, 1)
             img_lpng = read_png(img_path)
             self.assertTrue(img_lpng.equal(img_pil))
 
     def test_decode_png(self):
         for img_path in get_images(IMAGE_DIR, ".png"):
             img_pil = torch.from_numpy(np.array(Image.open(img_path)))
+            img_pil = img_pil.permute(2, 0, 1)
             size = os.path.getsize(img_path)
             img_lpng = decode_png(torch.from_file(img_path, dtype=torch.uint8, size=size))
             self.assertTrue(img_lpng.equal(img_pil))

torchvision/csrc/cpu/image/readjpeg_cpu.cpp

@@ -137,7 +137,7 @@ torch::Tensor decodeJPEG(const torch::Tensor& data) {
 
   jpeg_finish_decompress(&cinfo);
   jpeg_destroy_decompress(&cinfo);
-  return tensor;
+  return tensor.permute({2, 0, 1});
 }
 
 #endif // JPEG_FOUND

torchvision/csrc/cpu/image/readpng_cpu.cpp

@@ -79,6 +79,6 @@ torch::Tensor decodePNG(const torch::Tensor& data) {
     ptr += bytes;
   }
   png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
-  return tensor;
+  return tensor.permute({2, 0, 1});
 }
 #endif // PNG_FOUND