OpenCV Assertion failed type mismatch - node.js

Question

I am using node-opencv and I want to get norm for two PNG images, but I have this instead:
OpenCV Error: Assertion failed (src1.size == src2.size && src1.type()
== src2.type()) in norm, file /build/opencv-RI6cfE/opencv-2.4.9.1+dfsg1/modules/core/src/stat.cpp,
line 1978
sizes are equal, types are different. type() and channels() methods for first Mat return 16 and 3 and for second 24 and 4.
I tried to do convertGrayscale with both images and got "Error: Image is no 3-channel" (ok, second has 4 channels, but first?)
I also tried to do second.convertTo(second,16) but got
libpng warning: iCCP: known incorrect sRGB profile
and there was no effect, second.type() still returned 24
Is there some way to convert Mat of any type to some kind of grayscale?
I plan to process a lot of images of different types, and I need to compare them with norm as grayscales.
here is my script:
var Promise = require("bluebird")
, fs = Promise.promisifyAll(require('fs'))
, cv = require('./opencv-build/node-opencv/lib/opencv');
var readImage = Promise.promisify(cv.readImage);
var ImageSimilarity = Promise.promisify(cv.ImageSimilarity);;
var imgdir = __dirname+'/img/';
var img_o = imgdir + 'src/walken.png';
var img_d = imgdir + 'dst/walken.png';
readImage(img_o).
then(function(first){
readImage(img_d)
.then(second=>{
second.convertTo(second,16);//no effect and >libpng warning: iCCP: known incorrect sRGB profile
console.log("first",
first.size(),
first.type(),
first.channels(),
"second",
second.size(),
second.type(),
second.channels());
//second.convertGrayscale();//doesn't work Error: Image is no 3-channel
console.log(first.norm(second, cv.Constants.NORM_L2));
});
});
and this is the output:
libpng warning: iCCP: known incorrect sRGB profile first [ 963, 1848 ]
16 3 second [ 963, 1848 ] 24 4 OpenCV Error: Assertion failed
(src1.size == src2.size && src1.type() == src2.type()) in norm, file
/build/opencv-RI6cfE/opencv-2.4.9.1+dfsg1/modules/core/src/stat.cpp,
line 1978 terminate called after throwing an instance of
'cv::Exception' what():
/build/opencv-RI6cfE/opencv-2.4.9.1+dfsg1/modules/core/src/stat.cpp:1978:
error: (-215) src1.size == src2.size && src1.type() == src2.type() in
function norm
Aborted (core dumped)
I think that libpng warning changes nothing.
P.S.
I tried to convert both images to grayscale in GIMP, type and channels of both images become 0/1 and norm works as expected, I can't understand why opencv can't do it.

Answer 1

Finally I switched from node-opencv (which works with OpenCV v2.3.1 bit not 3.x) to opencv4nodejs (which works with OpenCV v3+)
And now norm just works well. There is still libpng warning, but it works correctly.
So looks like OpenCV now handles channels mismatch by itself.
Here is my code for opencv4nodejs:
const cv = require('opencv4nodejs');
var imgdir = __dirname+'/img/';
var img_o = imgdir + 'src/walken.png';
var img_d = imgdir + 'dst/walken.png';
var first = cv.imread(img_o);
var second = cv.imread(img_d);
console.log(first.norm(second), cv.NORM_L2);
As you see, this code now works synchronously, so it's looks cleaner.