libpng is linked despite being excluded in cmake

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I'm trying to generate very compact version of OpenCV and it generally works except libpng (8 MB) cannot be striped out of the resulting binary (iOS Framework), despite having specified -DBUILD_PNG=OFF

Is there any dependency by the included modules (actually it should not be)?

Merging libraries:
/works/opencv-master/ios/build/build-arm64-iphoneos/install/lib/libopencv_calib3d.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/lib/libopencv_features2d.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/lib/libopencv_core.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/lib/libopencv_video.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/lib/libopencv_imgproc.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/share/OpenCV/3rdparty/lib/liblibpng.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/share/OpenCV/3rdparty/lib/libzlib.a
/works/opencv-master/ios/build/build-arm64-iphoneos/install/share/OpenCV/3rdparty/lib/liblibjpeg-turbo.a