opencv on mbed
Image file reading and writing
Modules | |
C API | |
iOS glue | |
Enumerations | |
enum | ImreadModes { IMREAD_UNCHANGED = -1, IMREAD_GRAYSCALE = 0, IMREAD_COLOR = 1, IMREAD_ANYDEPTH = 2, IMREAD_ANYCOLOR = 4, IMREAD_LOAD_GDAL = 8, IMREAD_REDUCED_GRAYSCALE_2 = 16, IMREAD_REDUCED_COLOR_2 = 17, IMREAD_REDUCED_GRAYSCALE_4 = 32, IMREAD_REDUCED_COLOR_4 = 33, IMREAD_REDUCED_GRAYSCALE_8 = 64, IMREAD_REDUCED_COLOR_8 = 65 } |
Imread flags. More... | |
enum | ImwriteFlags { IMWRITE_JPEG_QUALITY = 1, IMWRITE_JPEG_PROGRESSIVE = 2, IMWRITE_JPEG_OPTIMIZE = 3, IMWRITE_JPEG_RST_INTERVAL = 4, IMWRITE_JPEG_LUMA_QUALITY = 5, IMWRITE_JPEG_CHROMA_QUALITY = 6, IMWRITE_PNG_COMPRESSION = 16, IMWRITE_PNG_STRATEGY = 17, IMWRITE_PNG_BILEVEL = 18, IMWRITE_PXM_BINARY = 32, IMWRITE_WEBP_QUALITY = 64 } |
Imwrite flags. More... | |
enum | ImwritePNGFlags { IMWRITE_PNG_STRATEGY_DEFAULT = 0, IMWRITE_PNG_STRATEGY_FILTERED = 1, IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY = 2, IMWRITE_PNG_STRATEGY_RLE = 3, IMWRITE_PNG_STRATEGY_FIXED = 4 } |
Imwrite PNG specific flags used to tune the compression algorithm. More... | |
Functions | |
CV_EXPORTS_W Mat | imread (const String &filename, int flags=IMREAD_COLOR) |
Loads an image from a file. | |
CV_EXPORTS_W bool | imreadmulti (const String &filename, std::vector< Mat > &mats, int flags=IMREAD_ANYCOLOR) |
Loads a multi-page image from a file. | |
CV_EXPORTS_W bool | imwrite (const String &filename, InputArray img, const std::vector< int > ¶ms=std::vector< int >()) |
Saves an image to a specified file. | |
CV_EXPORTS_W Mat | imdecode (InputArray buf, int flags) |
Reads an image from a buffer in memory. | |
CV_EXPORTS Mat | imdecode (InputArray buf, int flags, Mat *dst) |
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. | |
CV_EXPORTS_W bool | imencode (const String &ext, InputArray img, CV_OUT std::vector< uchar > &buf, const std::vector< int > ¶ms=std::vector< int >()) |
Encodes an image into a memory buffer. |
Enumeration Type Documentation
enum ImreadModes |
Imread flags.
- Enumerator:
Definition at line 64 of file imgcodecs.hpp.
enum ImwriteFlags |
Imwrite flags.
- Enumerator:
Definition at line 80 of file imgcodecs.hpp.
enum ImwritePNGFlags |
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.
- Enumerator:
Definition at line 102 of file imgcodecs.hpp.
Function Documentation
CV_EXPORTS_W Mat cv::imdecode | ( | InputArray | buf, |
int | flags | ||
) |
Reads an image from a buffer in memory.
The function imdecode reads an image from the specified buffer in the memory. If the buffer is too short or contains invalid data, the function returns an empty matrix ( Mat::data==NULL ).
See cv::imread for the list of supported formats and flags description.
- Note:
- In the case of color images, the decoded images will have the channels stored in **B G R** order.
- Parameters:
-
buf Input array or vector of bytes. flags The same flags as in cv::imread, see cv::ImreadModes.
CV_EXPORTS Mat cv::imdecode | ( | InputArray | buf, |
int | flags, | ||
Mat * | dst | ||
) |
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
- Parameters:
-
buf flags dst The optional output placeholder for the decoded matrix. It can save the image reallocations when the function is called repeatedly for images of the same size.
CV_EXPORTS_W bool cv::imencode | ( | const String & | ext, |
InputArray | img, | ||
CV_OUT std::vector< uchar > & | buf, | ||
const std::vector< int > & | params = std::vector< int >() |
||
) |
Encodes an image into a memory buffer.
The function imencode compresses the image and stores it in the memory buffer that is resized to fit the result. See cv::imwrite for the list of supported formats and flags description.
- Parameters:
-
ext File extension that defines the output format. img Image to be written. buf Output buffer resized to fit the compressed image. params Format-specific parameters. See cv::imwrite and cv::ImwriteFlags.
CV_EXPORTS_W Mat cv::imread | ( | const String & | filename, |
int | flags = IMREAD_COLOR |
||
) |
Loads an image from a file.
The function imread loads an image from the specified file and returns it. If the image cannot be read (because of missing file, improper permissions, unsupported or invalid format), the function returns an empty matrix ( Mat::data==NULL ).
Currently, the following file formats are supported:
- Windows bitmaps - \*.bmp, \*.dib (always supported)
- JPEG files - \*.jpeg, \*.jpg, \*.jpe (see the *Notes* section)
- JPEG 2000 files - \*.jp2 (see the *Notes* section)
- Portable Network Graphics - \*.png (see the *Notes* section)
- WebP - \*.webp (see the *Notes* section)
- Portable image format - \*.pbm, \*.pgm, \*.ppm \*.pxm, \*.pnm (always supported)
- Sun rasters - \*.sr, \*.ras (always supported)
- TIFF files - \*.tiff, \*.tif (see the *Notes* section)
- OpenEXR Image files - \*.exr (see the *Notes* section)
- Radiance HDR - \*.hdr, \*.pic (always supported)
- Raster and Vector geospatial data supported by Gdal (see the *Notes* section)
- Note:
- The function determines the type of an image by the content, not by the file extension.
- In the case of color images, the decoded images will have the channels stored in **B G R** order.
- On Microsoft Windows\* OS and MacOSX\*, the codecs shipped with an OpenCV image (libjpeg, libpng, libtiff, and libjasper) are used by default. So, OpenCV can always read JPEGs, PNGs, and TIFFs. On MacOSX, there is also an option to use native MacOSX image readers. But beware that currently these native image loaders give images with different pixel values because of the color management embedded into MacOSX.
- On Linux\*, BSD flavors and other Unix-like open-source operating systems, OpenCV looks for codecs supplied with an OS image. Install the relevant packages (do not forget the development files, for example, "libjpeg-dev", in Debian\* and Ubuntu\*) to get the codec support or turn on the OPENCV_BUILD_3RDPARTY_LIBS flag in CMake.
- In the case you set *WITH_GDAL* flag to true in CMake and IMREAD_LOAD_GDAL to load the image, then [GDAL](http://www.gdal.org) driver will be used in order to decode the image by supporting the following formats: [Raster](http://www.gdal.org/formats_list.html), [Vector](http://www.gdal.org/ogr_formats.html).
- Parameters:
-
filename Name of file to be loaded. flags Flag that can take values of cv::ImreadModes
CV_EXPORTS_W bool cv::imreadmulti | ( | const String & | filename, |
std::vector< Mat > & | mats, | ||
int | flags = IMREAD_ANYCOLOR |
||
) |
Loads a multi-page image from a file.
The function imreadmulti loads a multi-page image from the specified file into a vector of Mat objects.
- Parameters:
-
filename Name of file to be loaded. flags Flag that can take values of cv::ImreadModes, default with cv::IMREAD_ANYCOLOR. mats A vector of Mat objects holding each page, if more than one.
- See also:
- cv::imread
CV_EXPORTS_W bool cv::imwrite | ( | const String & | filename, |
InputArray | img, | ||
const std::vector< int > & | params = std::vector< int >() |
||
) |
Saves an image to a specified file.
The function imwrite saves the image to the specified file. The image format is chosen based on the filename extension (see cv::imread for the list of extensions). Only 8-bit (or 16-bit unsigned (CV_16U) in case of PNG, JPEG 2000, and TIFF) single-channel or 3-channel (with 'BGR' channel order) images can be saved using this function. If the format, depth or channel order is different, use Mat::convertTo , and cv::cvtColor to convert it before saving. Or, use the universal FileStorage I/O functions to save the image to XML or YAML format.
It is possible to store PNG images with an alpha channel using this function. To do this, create 8-bit (or 16-bit) 4-channel image BGRA, where the alpha channel goes last. Fully transparent pixels should have alpha set to 0, fully opaque pixels should have alpha set to 255/65535.
The sample below shows how to create such a BGRA image and store to PNG file. It also demonstrates how to set custom compression parameters :
#include <opencv2/opencv.hpp> 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<Vec4b>(i, j); bgra[0] = UCHAR_MAX; // Blue bgra[1] = saturate_cast<uchar>((float (mat.cols - j)) / ((float)mat.cols) * UCHAR_MAX); // Green bgra[2] = saturate_cast<uchar>((float (mat.rows - i)) / ((float)mat.rows) * UCHAR_MAX); // Red bgra[3] = saturate_cast<uchar>(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<int> 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; }
- Parameters:
-
filename Name of the file. img Image to be saved. params Format-specific parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ... .) see cv::ImwriteFlags
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