remove line throws nullpointer

[ghost]

I have an scanned document from which i am trying to remove lines. I am getting Nullpointer as
Leptonica1.pixThresholdToBinary(pixs, 170) returns Null (in LeptUtils.removeLines method . line 107).

if i try with the image available in test_data i.e. dave-orig.png everything works fine.

Any idea what could be the reason ?

[nguyenq]

Make sure the input image is grayscale.

[braj302019]

Thanks its working after converting image to gray scale.

Sample code:
Pix grayPix = Leptonica1.pixConvertRGBToGrayFast(pixs);