Want faster method to write an OpenCV Mat object

[Lawrence Tsang]

Hi All,

I have recently used the following code to write the content of a
Mat object :

m_yuv.put(0, 0, mFrame);
Imgproc.cvtColor(m_yuv, m_rgba, Imgproc.COLOR_YUV420sp2RGB, 4);
m_bmp = Bitmap.createBitmap(mFrameWidth, mFrameHeight,
Bitmap.Config.ARGB_8888);
Utils.matToBitmap(m_rgba, m_bmp);

// Write the bitmap to external storage.
if ( m_ExternalStorageAvailable && m_ExternalStorageWriteable ) {
File path = Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES);
File file = new File(path, "DemoCalibrationPicture_" + new
SimpleDateFormat ("yyyyMMddHHmmss").format(new Date()) + ".png");
try {
path.mkdirs();
FileOutputStream fOut = new FileOutputStream(file);
m_bmp.compress(Bitmap.CompressFormat.PNG, 100, fOut);
fOut.flush();
fOut.close();
Log.i(TAG, "m_bmp has been written to external storage.");
} catch (IOException e) {
Log.w(TAG, "Error writing : m_bmp" + file, e);
}
} else {
Log.i(TAG, "External Storage NOT available or writable.");
}

which use the mFrame data in "onPreviewFrame" callback, put the
data into the "m_yuv" Mat object, convert it to an Android Bitmap and
then write the Bitmap to external storage.

However, it takes 1 to 2 seconds to write the Mat object into
external storage which is a bit too slow for my application.

Does anyone know a faster method to write the Mat object to
disk ? Thanks for any suggestion

Lawrence

[陈卿]

I have the same problem before. when I use the android java-api ,it takes 10 seconds. and then I change it to C++ code and build with ndk....it's instant!!!

2011/12/31 Lawrence Tsang <tkw...@gmail.com>

[Lawrence Tsang]

Hi 陈卿 and All,

Thanks for your suggestion.

If ndk is used, which method do you use to write the Mat object,
"imwrite" or something else.

Lawrence

On Dec 31, 1:06 pm, 陈卿 <chenqing1...@gmail.com> wrote:
> I have the same problem before. when I use the android java-api ,it takes
> 10 seconds. and then I change it to C++ code and build with ndk....it's
> instant!!!
>

> 2011/12/31 Lawrence Tsang <tkwi...@gmail.com>

[陈卿]

I use this method !

if 1 channel mat...

(colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels() ];

if 4 channels mat...alpha is ignored!

(colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+0 ];

(colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+1 ];

(colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+2 ];

have a try! good luck!

2011/12/31 Lawrence Tsang <tkw...@gmail.com>

[陈卿]

you mean write to SD card?

[Lawrence Tsang]

Hi 陈卿 and All,

Yes, I mean writing a Mat object to SD card. I suppose to use

imwrite("/sdcard/Pictures/filename.png", m_yuv);

But I am not sure whether I could use "imwrite" this way in
Android NDK (as Android has some file permission issues, I am not sure
if NDK could write a file directly to an external storage location.)

Lawrence

On Dec 31, 2:10 pm, 陈卿 <chenqing1...@gmail.com> wrote:
> you mean write to SD card?
>

> 在 2011年12月31日 下午2:07，陈卿 <chenqing1...@gmail.com>写道：
>
>
>
>
>
>
>
> > I use this method !
> > if 1 channel mat...
> > (colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels() ];
>
> > if 4 channels mat...alpha is ignored!
> > (colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+0
> > ];
> > (colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+1
> > ];
> > (colorZoomImg.data + colorZoomImg.step * i)[j * colorZoomImg.channels()+2
> > ];
>
> > have a try! good luck!
>

> > 2011/12/31 Lawrence Tsang <tkwi...@gmail.com>

[陈卿]

of course not.....I use this android java api 

fileUtils.writeToSDFromInput(here is your save path&bitmap);

if using ndk , you should convert C++ mat to jintArray ,then convert it to bitmap.

[Lawrence Tsang]

Thanks 陈卿.

On Dec 31, 3:00 pm, 陈卿 <chenqing1...@gmail.com> wrote:
> of course not.....I use this android java api
>
> fileUtils.writeToSDFromInput(here is your save path&bitmap);
>
> if using ndk , you should convert C++ mat to jintArray ,then convert it to
> bitmap.
>

[陈卿]

it's my pleasure!!