# Sending correct mask for grabcut in python

**URL:** <https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602>\
**Category:** Uncategorized\
**Tags:** programming\
**Created:** [June 20, 2023, 6:42am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602 "2023-06-20T06:42:28Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Argha\_Chakraborty](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/argha_chakraborty/32/8055_2.png) [@Argha\_Chakraborty](https://forum.opencv.org/u/Argha_Chakraborty)\
**Post date:** [June 20, 2023, 6:42am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/1 "2023-06-20T06:42:28Z")

</div>

I am trying to send a mask for which the border pixel of the mask is 0 (sure background) and the rest of the pixels are at some gray level(say 120 as we do not know the sure foreground)

This is the function for finding the mask.

```auto
def maskImage(img):
    width = img.shape[1]
    height = img.shape[0]
    image = np.ones((height, width), dtype=np.uint8) * 120 #gray pixels
    # Set boundary pixels to black
    image[0, :] = 0 # Top boundary
    image[height - 1, :] = 0 # Bottom boundary
    image[:, 0] = 0 # Left boundary
    image[:, width - 1] = 0 # Right boundary
    _, image = cv2.threshold(image, 128,255,cv2.THRESH_BINARY)

```

Now , I want to call grabcut with this mask as initializer instead of rect.

```auto
def grabCut(img):
    imgcopy = img.copy()
    img = cv2.cvtColor(img,cv2.COLOR_RGBA2BGR)
    mask = np.zeros(img.shape[:2], np.uint8)
    m = maskImage(img)
    mask[m == 0] = 0
    bgdModel = np.zeros((1,65),np.float64)
    fgdModel = np.zeros((1,65),np.float64)
    rect = (0,0, img.shape[1]-1, img.shape[0]-1)
    mask = (0,0, mask.shape[1]-1, mask.shape[0]-1)
    mask, bgdModel, fgdModel = cv2.grabCut(img,mask,None,bgdModel,fgdModel,5,cv2.GC_INIT_WITH_MASK)
    mask2 = np.where((mask==2)|(mask==0),1,0).astype('uint8')
    img = img*mask2[:,:,np.newaxis]
    cv2.imwrite("grab.png", img)

```

With this I am getting this error:

cv2.error: OpenCV(3.4.2) /opt/concourse/worker/volumes/live/9523d527-1b9e-48e0-7ed0-a36adde286f0/volume/opencv-suite\_1535558719691/work/modules/imgproc/src/grabcut.cpp:328: error: (-5:Bad argument) mask must have CV\_8UC1 type in function ‘checkMask’

Need help fixing it.

---

<div class="post-metadata">

**Author:** ![berak](https://avatars.discourse-cdn.com/v4/letter/b/85f322/32.png) [@berak](https://forum.opencv.org/u/berak)\
**Post date:** [June 20, 2023, 7:21am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/2 "2023-06-20T07:21:50Z")

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> [@Argha\_Chakraborty](#):
>
> ```auto
> mask[m == 0] = 0
>     
> 
> ```

this is an array of boolean, not uint8

---

<div class="post-metadata">

**Author:** ![Argha\_Chakraborty](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/argha_chakraborty/32/8055_2.png) [@Argha\_Chakraborty](https://forum.opencv.org/u/Argha_Chakraborty)\
**Post date:** [June 20, 2023, 8:54am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/3 "2023-06-20T08:54:53Z")

</div>

how can I fix it? need some more inputs

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<div class="post-metadata">

**Author:** ![Argha\_Chakraborty](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/argha_chakraborty/32/8055_2.png) [@Argha\_Chakraborty](https://forum.opencv.org/u/Argha_Chakraborty)\
**Post date:** [June 20, 2023, 8:56am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/4 "2023-06-20T08:56:25Z")

</div>

I am following this tutorial [https://docs.opencv.org/3.4/d8/d83/tutorial\_py\_grabcut.html](https://docs.opencv.org/3.4/d8/d83/tutorial_py_grabcut.html)

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<div class="post-metadata">

**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [June 20, 2023, 10:46am UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/5 "2023-06-20T10:46:58Z")

</div>

_what_ is _that_ supposed to be?

> [@Argha\_Chakraborty](#):
>
> ```auto
> mask = (0,0, mask.shape[1]-1, mask.shape[0]-1)
> 
> ```

that’s not shown in the tutorial.

that’s not a mask. that’s a 4-tuple.

please think about the difference between a rectangle and a mask.

---

<div class="post-metadata">

**Author:** ![Argha\_Chakraborty](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/argha_chakraborty/32/8055_2.png) [@Argha\_Chakraborty](https://forum.opencv.org/u/Argha_Chakraborty)\
**Post date:** [June 20, 2023, 2:08pm UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/6 "2023-06-20T14:08:51Z")

</div>

Thanks for pointing this .

Now I have modified my grabCut function:

```auto
def grabCut1(img):
    imgcopy = img.copy()
    img = cv2.cvtColor(img,cv2.COLOR_RGBA2BGR)
    mask = np.zeros((img.shape[0], img.shape[1]), np.uint8)
    m = maskImage(img)
    mask[m == 0] = 0
    print("mask shape ", mask.shape)
    bgdModel = np.zeros((1,65),np.float64)
    fgdModel = np.zeros((1,65),np.float64)
    mask, bgdModel, fgdModel = cv2.grabCut(img,mask,None,bgdModel,fgdModel,5,cv2.GC_INIT_WITH_MASK)
    mask2 = np.where((mask==2)|(mask==0),1,0).astype('uint8')
    img = img*mask2[:,:,np.newaxis]
    cv2.imwrite("graby.png", img)

```

But still getting this error related to bgdModel, fgdModel.

> ", line 167, in run\_endpoint\_function  
> return await dependant.call(\*\*values)  
> File “./api.py”, line 37, in find\_contour  
> contours = grabCut1(img)  
> File “./api.py”, line 67, in grabCut1  
> mask, bgdModel, fgdModel = cv2.grabCut(img,mask,None,bgdModel,fgdModel,5,cv2.GC\_INIT\_WITH\_MASK)  
> cv2.error: OpenCV(3.4.2) /opt/concourse/worker/volumes/live/9523d527-1b9e-48e0-7ed0-a36adde286f0/volume/opencv-suite\_1535558719691/work/modules/imgproc/src/grabcut.cpp:380: error: (-215:Assertion failed) !bgdSamples.empty() && !fgdSamples.empty() in function ‘initGMMs’

---

<div class="post-metadata">

**Author:** ![Argha\_Chakraborty](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/argha_chakraborty/32/8055_2.png) [@Argha\_Chakraborty](https://forum.opencv.org/u/Argha_Chakraborty)\
**Post date:** [June 20, 2023, 3:54pm UTC](https://forum.opencv.org/t/sending-correct-mask-for-grabcut-in-python/13602/7 "2023-06-20T15:54:59Z")

</div>

In fact it is not working with the example given in the opencv doc. I used the same image as mask just for sanity testing.

```auto
import numpy as np
import cv2 as cv
from matplotlib import pyplot as plt
img = cv.imread('messi.jpg')
assert img is not None, "file could not be read, check with os.path.exists()"
mask = np.zeros(img.shape[:2],np.uint8)
bgdModel = np.zeros((1,65),np.float64)
fgdModel = np.zeros((1,65),np.float64)
newmask = cv.imread('messi.jpg', cv.IMREAD_GRAYSCALE)
assert newmask is not None, "file could not be read, check with os.path.exists()"
# wherever it is marked white (sure foreground), change mask=1
# wherever it is marked black (sure background), change mask=0
mask[newmask == 0] = 0
mask[newmask == 255] = 1
_ = cv.grabCut(img,mask,None,bgdModel,fgdModel,5,cv.GC_INIT_WITH_MASK)
mask = np.where((mask==2)|(mask==0),0,1).astype('uint8')
img = img*mask[:,:,np.newaxis]
plt.imshow(img),plt.colorbar(),plt.show()

```

Still getting:

> Traceback (most recent call last):  
> File “mask.py”, line 15, in   
> \_ = cv.grabCut(img,mask,None,bgdModel,fgdModel,5,cv.GC\_INIT\_WITH\_MASK)  
> cv2.error: OpenCV(3.4.2) /opt/concourse/worker/volumes/live/9523d527-1b9e-48e0-7ed0-a36adde286f0/volume/opencv-suite\_1535558719691/work/modules/imgproc/src/grabcut.cpp:380: error: (-215:Assertion failed) !bgdSamples.empty() && !fgdSamples.empty() in function ‘initGMMs’