opencv读写图像问题！
一、OpenCV中支持读取的图像格式：
1. Windows bitmaps \*.bmp, \*.dib
2. JPEG files \*.jpeg, \*.jpg, \*.jpe
3. JPEG 2000 files \*.jp2
4. Portable Network Graphics \*.png
5. WebP \*.webp
6. Portable image format \*.pbm, \*.pgm, \*.ppm \*.pxm, \*.pnm
7. Sun rasters \*.sr, \*.ras
8. TIFF files \*.tiff, \*.tif
9. OpenEXR Image files \*.exr
10. Radiance HDR \*.hdr, \*.pic
11. Raster and Vector geospatial data supported by GDAL
二、读取方式
cv2.imread(filename, flags=None)
其中：
flags = -1, 读取原始数据
flags = 0, 读取图像并将其转换为单通道灰度图，并且结果可能与使用cvtColor()函数的结果不同
flags = 1, 读取图像并将其转换为3通道图像，通道顺序为B、G、R
flags = 2, 读取并返回16位或32位图像（前提是图像必须有对应的深度，否则将转化为int8位图像返回
三、保存图像
cv2.imwrite(filename, img, params=None)
Imwrite flags
enum ImwriteFlags {
IMWRITE_JPEG_QUALITY = 1, //!< For JPEG, it can be a quality from 0 to 100 (the higher is the better). Default value is 95.
IMWRITE_JPEG_PROGRESSIVE = 2, //!< Enable JPEG features, 0 or 1, default is False.
IMWRITE_JPEG_OPTIMIZE = 3, //!< Enable JPEG features, 0 or 1, default is False.
IMWRITE_JPEG_RST_INTERVAL = 4, //!< JPEG restart interval, 0 - 65535, default is 0 - no restart.
IMWRITE_JPEG_LUMA_QUALITY = 5, //!< Separate luma quality level, 0 - 100, default is 0 - don't use.
IMWRITE_JPEG_CHROMA_QUALITY = 6, //!< Separate chroma quality level, 0 - 100, default is 0 - don't use.
IMWRITE_PNG_COMPRESSION = 16, //!< For PNG, it can be the compression level from 0 to 9. A higher value means a smaller size and longer compression time. If specified, strategy is changed to IMWRITE_PNG_STRATEGY_DEFAULT (Z_DEFAULT_STRATEGY). Default value is 1 (best speed setting).
IMWRITE_PNG_STRATEGY = 17, //!< One of cv::ImwritePNGFlags, default is IMWRITE_PNG_STRATEGY_RLE.
IMWRITE_PNG_BILEVEL = 18, //!< Binary level PNG, 0 or 1, default is 0.
IMWRITE_PXM_BINARY = 32, //!< For PPM, PGM, or PBM, it can be a binary format flag, 0 or 1. Default value is 1.
IMWRITE_WEBP_QUALITY = 64, //!< For WEBP, it can be a quality from 1 to 100 (the higher is the better). By default (without any parameter) and for quality above 100 the lossless compression is used.
IMWRITE_PAM_TUPLETYPE = 128,//!< For PAM, sets the TUPLETYPE field to the corresponding string value that is defined for the format
};
//! Imwrite PNG specific flags used to tune the compression algorithm.
/** These flags will be modify the way of PNG image compression and will be passed to the underlying zlib processing stage.
- The effect of IMWRITE_PNG_STRATEGY_FILTERED is to force more Huffman coding and less string matching; it is somewhat intermediate between IMWRITE_PNG_STRATEGY_DEFAULT and IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY.
- IMWRITE_PNG_STRATEGY_RLE is designed to be almost as fast as IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY, but give better compression for PNG image data.
- The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately.
- IMWRITE_PNG_STRATEGY_FIXED prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.
*/
enum ImwritePNGFlags {
IMWRITE_PNG_STRATEGY_DEFAULT = 0, //!< Use this value for normal data.
IMWRITE_PNG_STRATEGY_FILTERED = 1, //!< Use this value for data produced by a filter (or predictor).Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better.
IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY = 2, //!< Use this value to force Huffman encoding only (no string match).
IMWRITE_PNG_STRATEGY_RLE = 3, //!< Use this value to limit match distances to one (run-length encoding).
IMWRITE_PNG_STRATEGY_FIXED = 4 //!< Using this value prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.
};
//! Imwrite PAM specific tupletype flags used to define the 'TUPETYPE' field of a PAM file.
enum ImwritePAMFlags {
IMWRITE_PAM_FORMAT_NULL = 0,
IMWRITE_PAM_FORMAT_BLACKANDWHITE = 1,
IMWRITE_PAM_FORMAT_GRAYSCALE = 2,
IMWRITE_PAM_FORMAT_GRAYSCALE_ALPHA = 3,
IMWRITE_PAM_FORMAT_RGB = 4,
IMWRITE_PAM_FORMAT_RGB_ALPHA = 5,
};
注意使用imwire函数保存图像时，一般只能保存8位（或16位无符号型
使用此函数还可以保存带有alpha通道的png图片，需要首先创建一个8位或16位的4通道的图像BGRA，其中alpha通道放在最后，对于全透明的图像，其alpha通道值的应该设置为0，对于完全不透明的图像，其alpha通道的值应该设置为255/65535。C++版本的示例代码如下：
#include
using namespace cv;
using namespace std;
void createAlphaMat(Mat &mat)
{
CV_Assert(mat.channels() == 4);
for (int i = 0; i < mat.rows; ++i) {
for (int j = 0; j < mat.cols; ++j) {
Vec4b& bgra = mat.at(i, j);
bgra[0] = UCHAR_MAX; // Blue
bgra[1] = saturate_cast((float (mat.cols - j)) / ((float)mat.cols) * UCHAR_MAX); // Green
bgra[2] = saturate_cast((float (mat.rows - i)) / ((float)mat.rows) * UCHAR_MAX); // Red
bgra[3] = saturate_cast(0.5 * (bgra[1] + bgra[2])); // Alpha
}
}
}
int main(int argv, char **argc)
{
// Create mat with alpha channel
Mat mat(480, 640, CV_8UC4);
createAlphaMat(mat);
vector compression_params;
compression_params.push_back(IMWRITE_PNG_COMPRESSION);
compression_params.push_back(9);
try{
imwrite("alpha.png", mat, compression_params);
}
catch (cv::Exception& ex) {
fprintf(stderr, "Exception converting image to PNG format: %s\n", ex.what());
return 1;
}
fprintf(stdout, "Saved PNG file with alpha data.\n");
return 0;
}
如果你想保存其他数据类型的图像，可按照下列方式：
1.CV_16U格式的图像可以保存为：PNG、JPEG 2000、 TIFF 格式
2.CV_32F格式的图像可以保存为：TIFF、 OpenEXR、 Radiance HDR格式。