OpenCV Java中的灰度倒置图像答案

【问题标题】：Grayscaling inverted image in OpenCV JavaOpenCV Java中的灰度倒置图像
【发布时间】：2015-01-06 22:53:51
【问题描述】：

我想在 openCV 中将反转图像转换为灰度图像，我使用 this method 来反转 BGR 图像，但我收到有关 Imgproc.cvtColor 方法的错误。

这是日志：

01-06 13:43:01.085: E/cv::error()(8837): OpenCV Error: Assertion failed (scn == 3 || scn == 4) in void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int), file /home/reports/ci/slave_desktop/50-SDK/opencv/modules/imgproc/src/color.cpp, line 3737
01-06 13:43:01.095: E/org.opencv.imgproc(8837): imgproc::cvtColor_11() caught cv::Exception: /home/reports/ci/slave_desktop/50-SDK/opencv/modules/imgproc/src/color.cpp:3737: error: (-215) scn == 3 || scn == 4 in function void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int)
01-06 13:43:01.095: E/AndroidRuntime(8837): FATAL EXCEPTION: main
01-06 13:43:01.095: E/AndroidRuntime(8837): Process: com.example.irisrecog, PID: 8837
01-06 13:43:01.095: E/AndroidRuntime(8837): java.lang.RuntimeException: Unable to resume activity {com.example.irisrecog/com.example.irisrecog.MainActivity}: CvException [org.opencv.core.CvException: cv::Exception: /home/reports/ci/slave_desktop/50-SDK/opencv/modules/imgproc/src/color.cpp:3737: error: (-215) scn == 3 || scn == 4 in function void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int)
01-06 13:43:01.095: E/AndroidRuntime(8837): ]
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2850)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2879)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1288)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.os.Looper.loop(Looper.java:212)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.ActivityThread.main(ActivityThread.java:5151)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at java.lang.reflect.Method.invokeNative(Native Method)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at java.lang.reflect.Method.invoke(Method.java:515)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:875)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:691)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at dalvik.system.NativeStart.main(Native Method)
01-06 13:43:01.095: E/AndroidRuntime(8837): Caused by: CvException [org.opencv.core.CvException: cv::Exception: /home/reports/ci/slave_desktop/50-SDK/opencv/modules/imgproc/src/color.cpp:3737: error: (-215) scn == 3 || scn == 4 in function void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int)
01-06 13:43:01.095: E/AndroidRuntime(8837): ]
01-06 13:43:01.095: E/AndroidRuntime(8837):     at org.opencv.imgproc.Imgproc.cvtColor_1(Native Method)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at org.opencv.imgproc.Imgproc.cvtColor(Imgproc.java:4598)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at com.example.irisrecog.MainActivity.segmentasi(MainActivity.java:240)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at com.example.irisrecog.MainActivity.deteksiIrisMata(MainActivity.java:283)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at com.example.irisrecog.MainActivity.onResume(MainActivity.java:135)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.Activity.performResume(Activity.java:5310)
01-06 13:43:01.095: E/AndroidRuntime(8837):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2840)
01-06 13:43:01.095: E/AndroidRuntime(8837):     ... 10 more

下面是我对倒置图像进行灰度化的代码：

//invert matrix - bgrFrame
Mat invertedMat = new Mat(bgrFrame.rows(), bgrFrame.cols(), bgrFrame.type());
Mat invertColorMat = new Mat(bgrFrame.rows(), bgrFrame.cols(), bgrFrame.type(), new Scalar(255,255,255));
Core.subtract(invertColorMat, bgrFrame, invertedMat);
//grayscaling inverted matrix
Mat grayscaledMat = new Mat();
Imgproc.cvtColor(invertedMat, grayscaledMat, Imgproc.COLOR_BGR2GRAY); // this line caused an error

我的代码有错误吗？非常感谢

【问题讨论】：

您是否尝试过先转换为灰度然后反转？据我所知，没有理由减去三个通道然后进行转换。
您的bgrFrame 是否可能是BGRA？ afaik 是 android 上的标准类型。请尝试Imgproc.COLOR_BGRA2GRAY，也许可以调整您的Scalar(255,255,255)
@Mailerdaimon 我的目标是像this tutorial 那样检测瞳孔边界，该教程说我必须先反转图像而不是先灰度化。如果我先对其进行灰度化然后反转，是否有可能，结果与该教程中的相同？如果我错了，我很抱歉，我刚刚在 OpenCV 上开始了我的第一个项目，并且我只是按照那个教程进行操作。感谢您的帮助。
@Micka 我已经尝试过 Imgproc.COLOR_BGRA2GRAY，但仍然没有运气。感谢您的帮助。
你能打印invertedMat.type()和invertedMat.channels()吗？异常告诉您，据我所知，您的源 Mat 的通道数有问题...

标签： java android opencv image-processing

【解决方案1】：

您不需要手动反转图像，有一个阈值标志，它会自动执行此操作：

Mat grayscaledMat = new Mat();
Imgproc.cvtColor(bgrFrame, grayscaledMat, Imgproc.COLOR_BGR2GRAY);

Mat thresh = new Mat();
Imgproc.threshold(grayscaledMat, thresh, 30, 255, Imgproc.THRESH_BINARY_INV);

但是您的错误消息抱怨说，cvtColor 的输入既没有 3 个也没有 4 个通道，所以它要么是灰度，要么是一个完全空/无效的 img。

【讨论】：