使用 OpenCV 时无法将图像转换为灰度 [英] Can't convert image to grayscale when using OpenCV

问题描述

我有一个透明的徽标，我想使用 OpenCV 将其转换为灰度.我正在使用以下代码

I have a transparent logo that I want to convert to grayscale using OpenCV. I am using the following code

def to_grayscale(logo):
    gray = cv2.cvtColor(logo, cv2.COLOR_RGB2GRAY)
    blur = cv2.GaussianBlur(gray, (5, 5), 0)
    canny = cv2.Canny(blur, 50, 150)  # sick
    return canny

这是图像变量:

brand_logo = Image.open(current_dir + '/logos/' + logo_image, 'r').convert('RGBA')
brand_logo = to_grayscale(brand_logo)

这是错误:

TypeError: Expected Ptr<cv::UMat> for argument 'src'

我尝试使用 PIL 中的 .convert('L') 但它使其 90% 透明灰色.无论如何我能解决这个问题吗?

I tried to use .convert('L') from PIL but it makes it 90% transparent gray. Anyway I can fix this issue?

更新

def to_grayscale(logo):
    OCVim = np.array(logo)
    BGRim = cv2.cvtColor(OCVim, cv2.COLOR_RGB2BGR)
    blurry = cv2.GaussianBlur(BGRim, (5, 5), 0)
    canny = cv2.Canny(blurry, 50, 150)
    PILim = Image.fromarray(canny)
    return PILim

推荐答案

你不必要地混合了 OpenCV 和 PIL/Pillow 并且会混淆你自己.如果你用 PIL 打开一个图像，你会得到一个 PIL 图像，这对 OpenCV 来说是双重没有用的，因为:

You are mixing OpenCV and PIL/Pillow unnecessarily and will confuse yourself. If you open an image with PIL, you will get a PIL Image which is doubly no use for OpenCV because:

• OpenCV 需要 Numpy 数组，而不是 PIL Images 和
• OpenCV 使用 BGR 排序，而不是 PIL 使用的 RGB 排序.

• OpenCV expects Numpy arrays, not PIL Images, and
• OpenCV uses BGR ordering, not RGB ordering like PIL uses.

同样适用于保存图像.

有三种可能的解决方案:

There are three possible solutions:

• 坚持PIL
• 坚持使用 OpenCV
• 每次在两个包之间移动时都进行转换.

从PIL Image转换为OpenCV的Numpy数组:

OCVim = np.array(PILim)

要将OpenCV的Numpy array转换为PIL Image:

PILim = Image.fromarray(OCVim)

---

要反转颜色顺序，显然不需要灰度，请使用:

---

To reverse the colour ordering, not necessary with greyscale obviously, either use:

BGRim = cv2.cvtColor(RGBim, cv2.COLOR_RGB2BGR)

或使用负的 Numpy 步幅:

or use a negative Numpy stride:

BGRim = RGBim[..., ::-1]

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