>&
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:
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)
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
driver will be used in order to decode the image by supporting the following formats:
Raster
,
Vector
.
If EXIF information are embedded in the image file, the EXIF orientation will be taken into account and thus the image will be rotated accordingly except if the flag
IMREAD_IGNORE_ORIENTATION
is passed.
Parameters:
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:
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:
