base64ToMat failing with JPEG image on iOS

[HugoBde]

I am trying to feed a base64 image into a model, and I'm trying to use OpenCV to convert the base64 image data to a Float32Array as follow (example taken from another issue):

const matImage = OpenCV.base64ToMat(base64String);
cv.OpenCV.invoke('convertTo', matImage, matImage, DataTypes.CV_32F, 1 / 255);
const { buffer, channels, cols, rows } = cv.OpenCV.matToBuffer(matImage, 'float32');

However, on iOS, I end up with an empty buffer, channels is 1, cols and rows are both 0.

I tried some different inputs on both platforms and I noticed that this issue only happens when the base64 string represents a JPEG image, and on iOS.

Minimal reproducible example:

// Both base64 strings can be checked for validity here: https://base64.guru/converter/decode/image

// Should be a 8x8 pixels grayscale image
const jpegImageString = "/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAMCAgICAgMCAgIDAwMDBAYEBAQEBAgGBgUGCQgKCgkICQkKDA8MCgsOCwkJDRENDg8QEBEQCgwSExIQEw8QEBD/wAALCAAIAAgBAREA/8QAFAABAAAAAAAAAAAAAAAAAAAACP/EAB4QAAEBCQAAAAAAAAAAAAAAABETEhUhN0FhZYSS/9oACAEBAAA/AH7JbMvnXSS7aKtgKmH/2Q=="

// Should be a 3 channels 8x8 image
const pngImageString = "iVBORw0KGgoAAAANSUhEUgAAAAgAAAAIAQMAAAD+wSzIAAAABlBMVEX///+/v7+jQ3Y5AAAADklEQVQI12P4AIX8EAgALgAD/aNpbtEAAAAASUVORK5CYII="

const jpegImage = OpenCV.base64ToMat(jpegImageString);
// buffer is empty
const { buffer, channels, cols, rows } = cv.OpenCV.matToBuffer(matImage, 'uint8'); 

const pngImage = OpenCV.base64ToMat(pngImageString);
// buffer is filled, channels == 3, cols and rows == 8
const { buffer, channels, cols, rows } = cv.OpenCV.matToBuffer(matImage, 'uint8'); 

As stated above, this issue only seems to happen on iOS, the same code on my Android device will produce the expected result for the JPEG image.

[imelos]

I ran into the same issue. As a temporary workaround, I convert the image to PNG before calling base64ToMat.