[英]OpenCV using cvImageCreate() with grayscale image fails, and resizing usually fails
我有這樣的代碼,它從緩沖區1byte,8bits位圖加載灰度圖像。 然后,它將調整此圖像的大小。
int resizeBitmap(const unsigned char *inData, const size_t inDataLength, const size_t inWidth, const size_t inHeight,
const int bitDepth, const int noOfChannels, unsigned char **outData, size_t *outDataLength, const size_t outWidth, const size_t outHeight) {
// create input image
IplImage *inImage = cvCreateImage(cvSize(inWidth, inHeight), bitDepth, noOfChannels);
cvSetData(inImage, inData, inImage->widthStep);
// show input image
cvNamedWindow("OpenCV Input Image", CV_WINDOW_FREERATIO);
cvShowImage("OpenCV Input Image", inImage);
cvWaitKey(0);
cvDestroyWindow("OpenCV Input Image");
/* */
// create output image
IplImage *outImage = cvCreateImage(cvSize(outWidth, outHeight), inImage->depth, inImage->nChannels);
// select interpolation type
double scaleFactor = (((double) outWidth)/inWidth + ((double) outHeight)/inHeight)/2;
int interpolation = (scaleFactor > 1.0) ? CV_INTER_LINEAR : CV_INTER_AREA;
// resize from input image to output image
cvResize(inImage, outImage, interpolation);
/* // show output image
cvNamedWindow("OpenCV Output Image", CV_WINDOW_FREERATIO);
cvShowImage("OpenCV Output Image", outImage);
cvWaitKey(0);
cvDestroyWindow("OpenCV Output Image");
*/
// get raw data from output image
int step = 0;
CvSize size;
cvGetRawData(outImage, outData, &step, &size);
*outDataLength = step*size.height;
cvReleaseImage(&inImage);
cvReleaseImage(&outImage);
return 0;
}
我在這里使用bitDepth = 8和noOfChannels =1。加載的圖像是:
由於程序通常會因以下錯誤而失敗,因此此輸出並不總是可以寫入:
OpenCV Error: Bad number of channels (Source image must have 1, 3 or 4 channels) in cvConvertImage, file /tmp/opencv-20160915-26910-go28a5/opencv-2.4.13/modules/highgui/src/utils.cpp, line 611
libc++abi.dylib: terminating with uncaught exception of type cv::Exception: /tmp/opencv-20160915-26910-go28a5/opencv-2.4.13/modules/highgui/src/utils.cpp:611: error: (-15) Source image must have 1, 3 or 4 channels in function cvConvertImage
我將附加調試器輸出,因為有一個有趣的情況,因為我正在傳遞大小為528480的灰度緩沖區,該緩沖區等於1個字節* 1101 * 480,但是在cvCreateImage之后,里面有imageSize 529920,widthStep為1104! 也許這是此圖像的問題,但是為什么呢?
此問題與IplImage的widthstep和width有關。 Opencv將圖像填充為4個字節的倍數的widthstep。 在這里,opencv使用的寬度為1101,寬度為1104。但是,當從位圖寫入IplImage時,每行寫入的像素很少(注意從左上角到右下角的對角線)。
請注意,圖像沒有傾斜。 只是每隔一行向左移一點(3個像素),從而產生剪切轉換的想法。
您提供的寬度也可能小於Bitmap的寬度。
在此處查看文檔並搜索填充。 您可以嘗試按行復制所有列數據。
為什么崩潰:有時,opencv最終會讀取到位圖緩沖區之外,並且可能會碰到無法觸及的內存地址,從而導致異常。
注意:位圖可能還具有填充,從中您會收到黑色對角線。
基於答案saurabheights,我編寫了將每個位圖行填充到行中任何給定的字節多樣性的過程。
int padBitmap(const unsigned char *data, const size_t dataLength, const size_t width, const size_t height,
const int bitDepth, const int noOfChannels, unsigned char **paddedData, size_t *paddedDataLength, const size_t row_multiple) {
size_t row_length = (width*noOfChannels*bitDepth)/CHAR_BIT;
size_t row_padding_size = row_multiple - row_length % row_multiple;
if(row_padding_size == 0) return 0;
size_t new_row_length = row_length + row_padding_size;
size_t newDataLength = height * new_row_length;
unsigned char *newData = malloc(sizeof(unsigned char) *newDataLength);
unsigned char padding[3] = {0, 0, 0};
for(int i=0; i<height; i++) {
memcpy(newData + i*new_row_length, data + i*row_length, row_length);
memcpy(newData + i*new_row_length + row_length, padding, row_padding_size);
}
*paddedData = newData;
*paddedDataLength = newDataLength;
return row_padding_size;
}
現在,在將位圖傳遞給resizeBitmap()之前,我要進行以下填充:
unsigned char *paddedData = 0;
size_t paddedDataLength = 0;
int padding = padBitmap(gData, gDataLength, width, height, PNG_BIT_DEPTH_8, GRAYSCALE_COMPONENTS_PER_PIXEL, &paddedData, &paddedDataLength, 4);
width += padding;
我使用的是paddedData
位圖。 它似乎正常工作
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