I have to provide a YUV(NV21) byte array to a recognition solution and I'd like, to reduce processing time, to down scale the preview frame.
From solutions gathered here and there on SO, I manage to convert on a 1:1 ratio and I get recognition hits. But if I'd like to scale the intermediate bitmap down, I get no result. Even if I scale it down to 95% only.
Any help would be appreciated.
Thus, every 400-ish ms I take the preview frame to convert it asynchronously. I convert it to ARGB using RenderScript, scale it down and then convert it back.
// Camera callback
#Override
public void onPreviewFrame(byte[] frame, Camera camera) {
if (camera != null) {
// Debounce
if ((System.currentTimeMillis() - mStart) > 400) {
mStart = System.currentTimeMillis();
Camera.Size size = camera.getParameters().getPreviewSize();
new FrameScaleAsyncTask(frame, size.width, size.height).execute();
}
}
if (mCamera != null) {
mCamera.addCallbackBuffer(mBuffer);
}
}
// In FrameScaleAsyncTask
#Override
protected Void doInBackground(Void... params) {
// Create YUV type for in-allocation
Type yuvType = new Type.Builder(mRenderScript, Element.U8(mRenderScript))
.setX(mFrame.length)
.create();
mAllocationIn = Allocation.createTyped(mRenderScript, yuvType, Allocation.USAGE_SCRIPT);
// Create ARGB-8888 type for out-allocation
Type rgbType = new Type.Builder(mRenderScript, Element.RGBA_8888(mRenderScript))
.setX(mWidth)
.setY(mHeight)
.create();
mAllocationOut = Allocation.createTyped(mRenderScript, rgbType, Allocation.USAGE_SCRIPT);
// Copy frame data into in-allocation
mAllocationIn.copyFrom(mFrame);
// Set script input and fire !
mScript.setInput(mAllocationIn);
mScript.forEach(mAllocationOut);
// Create a bitmap of camera preview size (see camera setup) and copy out-allocation to it
Bitmap bitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);
mAllocationOut.copyTo(bitmap);
// Scale bitmap down
double scaleRatio = 1;
Bitmap scaledBitmap = Bitmap.createScaledBitmap(
bitmap,
(int) (bitmap.getWidth() * scaleRatio),
(int) (bitmap.getHeight() * scaleRatio),
false
);
bitmap.recycle();
int size = scaledBitmap.getRowBytes() * scaledBitmap.getHeight();
int scaledWidth = scaledBitmap.getWidth();
int scaledHeight = scaledBitmap.getHeight();
int[] pixels = new int[scaledWidth * scaledHeight];
// Put bitmap pixels into an int array
scaledBitmap.getPixels(pixels, 0, scaledWidth, 0, 0, scaledWidth, scaledHeight);
mFrame = new byte[pixels.length * 3 / 2];
ImageHelper.encodeYUV420SPAlt(mFrame, pixels, scaledWidth, scaledHeight);
return null;
}
The RGB to YUV algorithm (see : this answer ):
public static void encodeYUV420SPAlt(byte[] yuv420sp, int[] argb, int width, int height) {
final int frameSize = width * height;
int yIndex = 0;
int uvIndex = frameSize;
int a, R, G, B, Y, U, V;
int index = 0;
for (int j = 0; j < height; j++) {
for (int i = 0; i < width; i++) {
a = (argb[index] & 0xff000000) >> 24; // a is not used obviously
R = (argb[index] & 0xff0000) >> 16;
G = (argb[index] & 0xff00) >> 8;
B = (argb[index] & 0xff) >> 0;
// well known RGB to YUV algorithm
Y = ((66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
U = ((-38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
V = ((112 * R - 94 * G - 18 * B + 128) >> 8) + 128;
// NV21 has a plane of Y and interleaved planes of VU each sampled by a factor of 2
// meaning for every 4 Y pixels there are 1 V and 1 U. Note the sampling is every other
// pixel AND every other scanline.
yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0 : ((Y > 255) ? 255 : Y));
if (j % 2 == 0 && index % 2 == 0) {
yuv420sp[uvIndex++] = (byte) ((V < 0) ? 0 : ((V > 255) ? 255 : V));
yuv420sp[uvIndex++] = (byte) ((U < 0) ? 0 : ((U > 255) ? 255 : U));
}
index++;
}
}
}
I finally end up resizing my image (as a OpenCV.Mat) directly in C++. This was way easier and faster.
Size size(correctedWidth, correctedHeight);
Mat dst;
resize(image, dst, size);
How can I convert Bitmap created using getDrawingCache() to YUV420planar format ?
The bitmap is created from a custom view like this
view.setDrawingCacheEnabled(true);
bitmap = Bitmap.createScaledBitmap(board.getDrawingCache(), 320, 240, true);
board.setDrawingCacheEnabled(false);
This question is similar but doesn't give the same format that I am looking for.
Convert bitmap array to YUV (YCbCr NV21).
Thanks in advance.
A bit of reading into YUV formats helped me figure it out. I just had to modify a tiny bit of the code linked above. For anyone who has the same doubt
void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width, int height) {
final int frameSize = width * height;
int yIndex = 0;
int uIndex = frameSize;
int vIndex = frameSize+((yuv420sp.length-frameSize)/2);
System.out.println(yuv420sp.length+" "+frameSize);
int a, R, G, B, Y, U, V;
int index = 0;
for (int j = 0; j < height; j++) {
for (int i = 0; i < width; i++) {
a = (argb[index] & 0xff000000) >> 24; // a is not used obviously
R = (argb[index] & 0xff0000) >> 16;
G = (argb[index] & 0xff00) >> 8;
B = (argb[index] & 0xff) >> 0;
// well known RGB to YUV algorithm
Y = ( ( 66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
U = ( ( -38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
V = ( ( 112 * R - 94 * G - 18 * B + 128) >> 8) + 128;
// NV21 has a plane of Y and interleaved planes of VU each sampled by a factor of 2
// meaning for every 4 Y pixels there are 1 V and 1 U. Note the sampling is every other
// pixel AND every other scanline.
yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0 : ((Y > 255) ? 255 : Y));
if (j % 2 == 0 && index % 2 == 0) {
yuv420sp[uIndex++] = (byte)((U<0) ? 0 : ((U > 255) ? 255 : U));
yuv420sp[vIndex++] = (byte)((V<0) ? 0 : ((V > 255) ? 255 : V));
}
index ++;
}
}
}
I am capturing image using SurfaceView and getting Yuv Raw preview data in public void onPreviewFrame4(byte[] data, Camera camera)
I have to perform some image preprocessing in onPreviewFrame so i need to convert Yuv preview data to RGB data than image preprocessing and back to Yuv data.
I have used both function for encoding and decoding Yuv data to RGB as following :
public void onPreviewFrame(byte[] data, Camera camera) {
Point cameraResolution = configManager.getCameraResolution();
if (data != null) {
Log.i("DEBUG", "data Not Null");
// Preprocessing
Log.i("DEBUG", "Try For Image Processing");
Camera.Parameters mParameters = camera.getParameters();
Size mSize = mParameters.getPreviewSize();
int mWidth = mSize.width;
int mHeight = mSize.height;
int[] mIntArray = new int[mWidth * mHeight];
// Decode Yuv data to integer array
decodeYUV420SP(mIntArray, data, mWidth, mHeight);
// Converting int mIntArray to Bitmap and
// than image preprocessing
// and back to mIntArray.
// Encode intArray to Yuv data
encodeYUV420SP(data, mIntArray, mWidth, mHeight);
}
}
static public void decodeYUV420SP(int[] rgba, byte[] yuv420sp, int width,
int height) {
final int frameSize = width * height;
for (int j = 0, yp = 0; j < height; j++) {
int uvp = frameSize + (j >> 1) * width, u = 0, v = 0;
for (int i = 0; i < width; i++, yp++) {
int y = (0xff & ((int) yuv420sp[yp])) - 16;
if (y < 0)
y = 0;
if ((i & 1) == 0) {
v = (0xff & yuv420sp[uvp++]) - 128;
u = (0xff & yuv420sp[uvp++]) - 128;
}
int y1192 = 1192 * y;
int r = (y1192 + 1634 * v);
int g = (y1192 - 833 * v - 400 * u);
int b = (y1192 + 2066 * u);
if (r < 0)
r = 0;
else if (r > 262143)
r = 262143;
if (g < 0)
g = 0;
else if (g > 262143)
g = 262143;
if (b < 0)
b = 0;
else if (b > 262143)
b = 262143;
// rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) &
// 0xff00) | ((b >> 10) & 0xff);
// rgba, divide 2^10 ( >> 10)
rgba[yp] = ((r << 14) & 0xff000000) | ((g << 6) & 0xff0000)
| ((b >> 2) | 0xff00);
}
}
}
static public void encodeYUV420SP_original(byte[] yuv420sp, int[] rgba,
int width, int height) {
final int frameSize = width * height;
int[] U, V;
U = new int[frameSize];
V = new int[frameSize];
final int uvwidth = width / 2;
int r, g, b, y, u, v;
for (int j = 0; j < height; j++) {
int index = width * j;
for (int i = 0; i < width; i++) {
r = (rgba[index] & 0xff000000) >> 24;
g = (rgba[index] & 0xff0000) >> 16;
b = (rgba[index] & 0xff00) >> 8;
// rgb to yuv
y = (66 * r + 129 * g + 25 * b + 128) >> 8 + 16;
u = (-38 * r - 74 * g + 112 * b + 128) >> 8 + 128;
v = (112 * r - 94 * g - 18 * b + 128) >> 8 + 128;
// clip y
yuv420sp[index++] = (byte) ((y < 0) ? 0 : ((y > 255) ? 255 : y));
U[index] = u;
V[index++] = v;
}
}
The problem is that encoding and decoding Yuv data might have some mistake because if i skip the preprocessing step than also encoded Yuv data are differ from original data of PreviewCallback.
Please help me to resolve this issue. I have to used this code in OCR scanning so i need to implement this type of logic.
If any other way of doing same thing than please provide me.
Thanks in advance. :)
Although the documentation suggests that you can set which format the image data should arrive from the camera in, in practice you often have a choice of one: NV21, a YUV format. For lots of information on this format see http://www.fourcc.org/yuv.php#NV21 and for information on the theory behind converting it to RGB see http://www.fourcc.org/fccyvrgb.php. There is a picture based explanation at Extract black and white image from android camera's NV21 format. There is an android specific section on a wikipedia page about the subject (thanks #AlexCohn): YUV#Y'UV420sp (NV21) to RGB conversion (Android).
However, once you've set up your onPreviewFrame routine, the mechanics of going from the byte array it sends you to useful data is somewhat, ummmm, unclear. From API 8 onwards, the following solution is available, to get to a ByteStream holiding a JPEG of the image (compressToJpeg is the only conversion option offered by YuvImage):
// pWidth and pHeight define the size of the preview Frame
ByteArrayOutputStream out = new ByteArrayOutputStream();
// Alter the second parameter of this to the actual format you are receiving
YuvImage yuv = new YuvImage(data, ImageFormat.NV21, pWidth, pHeight, null);
// bWidth and bHeight define the size of the bitmap you wish the fill with the preview image
yuv.compressToJpeg(new Rect(0, 0, bWidth, bHeight), 50, out);
This JPEG may then need to be converted into the format you want. If you want a Bitmap:
byte[] bytes = out.toByteArray();
Bitmap bitmap= BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
If, for whatever reason, you are unable to do this, you can do the conversion manually. Some problems to be overcome in doing this:
The data arrives in a byte array. By definition, bytes are signed numbers, meaning that they go from -128 to 127. However, the data is actually unsigned bytes (0 to 255). If this isn't dealt with, the outcome is doomed to have some odd clipping effects.
The data is in a very specific order (as per the previously mentioned web pages) and each pixel needs to be extracted carefully.
Each pixel needs to be put into the right place on a bitmap, say. This also requires a rather messy (in my view) approach of building a buffer of the data and then filling a bitmap from it.
In principle, the values should be stored [16..240], but it appears that they are stored [0..255] in the data sent to onPreviewFrame
Just about every web page on the matter proposes different coefficients, even allowing for [16..240] vs [0..255] options.
If you've actually got NV12 (another variant on YUV420), then you will need to swap the reads for U and V.
I present a solution (which seems to work), with requests for corrections, improvements and ways of making the whole thing less costly to run. I have set it out to hopefully make clear what is happening, rather than to optimise it for speed. It creates a bitmap the size of the preview image:
The data variable is coming from the call to onPreviewFrame
// Define whether expecting [16..240] or [0..255]
boolean dataIs16To240 = false;
// the bitmap we want to fill with the image
Bitmap bitmap = Bitmap.createBitmap(imageWidth, imageHeight, Bitmap.Config.ARGB_8888);
int numPixels = imageWidth*imageHeight;
// the buffer we fill up which we then fill the bitmap with
IntBuffer intBuffer = IntBuffer.allocate(imageWidth*imageHeight);
// If you're reusing a buffer, next line imperative to refill from the start,
// if not good practice
intBuffer.position(0);
// Set the alpha for the image: 0 is transparent, 255 fully opaque
final byte alpha = (byte) 255;
// Holding variables for the loop calculation
int R = 0;
int G = 0;
int B = 0;
// Get each pixel, one at a time
for (int y = 0; y < imageHeight; y++) {
for (int x = 0; x < imageWidth; x++) {
// Get the Y value, stored in the first block of data
// The logical "AND 0xff" is needed to deal with the signed issue
float Y = (float) (data[y*imageWidth + x] & 0xff);
// Get U and V values, stored after Y values, one per 2x2 block
// of pixels, interleaved. Prepare them as floats with correct range
// ready for calculation later.
int xby2 = x/2;
int yby2 = y/2;
// make this V for NV12/420SP
float U = (float)(data[numPixels + 2*xby2 + yby2*imageWidth] & 0xff) - 128.0f;
// make this U for NV12/420SP
float V = (float)(data[numPixels + 2*xby2 + 1 + yby2*imageWidth] & 0xff) - 128.0f;
if (dataIs16To240) {
// Correct Y to allow for the fact that it is [16..235] and not [0..255]
Y = 1.164*(Y - 16.0);
// Do the YUV -> RGB conversion
// These seem to work, but other variations are quoted
// out there.
R = (int)(Yf + 1.596f*V);
G = (int)(Yf - 0.813f*V - 0.391f*U);
B = (int)(Yf + 2.018f*U);
}
else {
// No need to correct Y
// These are the coefficients proposed by #AlexCohn
// for [0..255], as per the wikipedia page referenced
// above
R = (int)(Yf + 1.370705f*V);
G = (int)(Yf - 0.698001f*V - 0.337633f*U);
B = (int)(Yf + 1.732446f*U);
}
// Clip rgb values to 0-255
R = R < 0 ? 0 : R > 255 ? 255 : R;
G = G < 0 ? 0 : G > 255 ? 255 : G;
B = B < 0 ? 0 : B > 255 ? 255 : B;
// Put that pixel in the buffer
intBuffer.put(alpha*16777216 + R*65536 + G*256 + B);
}
}
// Get buffer ready to be read
intBuffer.flip();
// Push the pixel information from the buffer onto the bitmap.
bitmap.copyPixelsFromBuffer(intBuffer);
As #Timmmm points out below, you could do the conversion in int by multiplying the scaling factors by 1000 (ie. 1.164 becomes 1164) and then dividng the end results by 1000.
Why not specify that camera preview should provide RGB images?
i.e. Camera.Parameters.setPreviewFormat(ImageFormat.RGB_565);
You can use RenderScript -> ScriptIntrinsicYuvToRGB
Kotlin Sample
val rs = RenderScript.create(CONTEXT_HERE)
val yuvToRgbIntrinsic = ScriptIntrinsicYuvToRGB.create(rs, Element.U8_4(rs))
val yuvType = Type.Builder(rs, Element.U8(rs)).setX(byteArray.size)
val inData = Allocation.createTyped(rs, yuvType.create(), Allocation.USAGE_SCRIPT)
val rgbaType = Type.Builder(rs, Element.RGBA_8888(rs)).setX(width).setY(height)
val outData = Allocation.createTyped(rs, rgbaType.create(), Allocation.USAGE_SCRIPT)
inData.copyFrom(byteArray)
yuvToRgbIntrinsic.setInput(inData)
yuvToRgbIntrinsic.forEach(outData)
val bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
outData.copyTo(bitmap)
After some tests on Samsung S4 mini fastest code is (120% faster then Neil's [floats!] and 30% faster then original Hitesh's):
static public void decodeYUV420SP(int[] rgba, byte[] yuv420sp, int width,
int height) {
final int frameSize = width * height;
// define variables before loops (+ 20-30% faster algorithm o0`)
int r, g, b, y1192, y, i, uvp, u, v;
for (int j = 0, yp = 0; j < height; j++) {
uvp = frameSize + (j >> 1) * width;
u = 0;
v = 0;
for (i = 0; i < width; i++, yp++) {
y = (0xff & ((int) yuv420sp[yp])) - 16;
if (y < 0)
y = 0;
if ((i & 1) == 0) {
v = (0xff & yuv420sp[uvp++]) - 128;
u = (0xff & yuv420sp[uvp++]) - 128;
}
y1192 = 1192 * y;
r = (y1192 + 1634 * v);
g = (y1192 - 833 * v - 400 * u);
b = (y1192 + 2066 * u);
// Java's functions are faster then 'IFs'
r = Math.max(0, Math.min(r, 262143));
g = Math.max(0, Math.min(g, 262143));
b = Math.max(0, Math.min(b, 262143));
// rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) &
// 0xff00) | ((b >> 10) & 0xff);
// rgba, divide 2^10 ( >> 10)
rgba[yp] = ((r << 14) & 0xff000000) | ((g << 6) & 0xff0000)
| ((b >> 2) | 0xff00);
}
}
}
Speed is comparable to YuvImage.compressToJpeg() with ByteArrayOutputStream as output (30-50 ms for 640x480 image).
Result: Samsung S4 mini (2x1.7GHz) can't compress to JPEG/convert YUV to RGB in real time (640x480#30fps)
Java implementation is 10 times slow than the c version, I suggest you use GPUImage library or just move this part of code.
There is a android version of GPUImage:
https://github.com/CyberAgent/android-gpuimage
You can include this library if you use gradle, and call the method:
GPUImageNativeLibrary.YUVtoRBGA( inputArray, WIDTH, HEIGHT, outputArray);
I compare the time, for a NV21 image which is 960x540, use above java code, it cost 200ms+, with GPUImage version, just 10ms~20ms.
You can use ColorHelper library for this:
using ColorHelper;
YUV yuv = new YUV(0.1, 0.1, 0.2);
RGB rgb = ColorConverter.YuvToRgb(yuv);
Links:
Github
Nuget
Fixup the above code snippet
static public void decodeYUV420SP(int[] rgba, byte[] yuv420sp, int width,
int height) {
final int frameSize = width * height;
int r, g, b, y1192, y, i, uvp, u, v;
for (int j = 0, yp = 0; j < height; j++) {
uvp = frameSize + (j >> 1) * width;
u = 0;
v = 0;
for (i = 0; i < width; i++, yp++) {
y = (0xff & ((int) yuv420sp[yp])) - 16;
if (y < 0)
y = 0;
if ((i & 1) == 0) {
// above answer is wrong at the following lines. just swap ***u*** and ***v***
u = (0xff & yuv420sp[uvp++]) - 128;
v = (0xff & yuv420sp[uvp++]) - 128;
}
y1192 = 1192 * y;
r = (y1192 + 1634 * v);
g = (y1192 - 833 * v - 400 * u);
b = (y1192 + 2066 * u);
r = Math.max(0, Math.min(r, 262143));
g = Math.max(0, Math.min(g, 262143));
b = Math.max(0, Math.min(b, 262143));
// combine ARGB
rgba[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) & 0xff00)
| ((b >> 10) | 0xff);
}
}
}
Try RenderScript ScriptIntrinsicYuvToRGB, which comes with JellyBean 4.2 (Api 17+).
https://developer.android.com/reference/android/renderscript/ScriptIntrinsicYuvToRGB.html
On Nexus 7 (2013, JellyBean 4.3) a 1920x1080 image conversion (full HD camera preview) takes about 7 ms.
You can get the bitmap directly from the TextureView. Which is really fast.
Bitmap bitmap = textureview.getBitmap()
After reading many suggested links, articles, etc. I found the following great Android example app which captures the YUV Image from the camera and converts it into RGB Bitmap:
https://github.com/android/camera-samples/tree/main/CameraXTfLite
Nice things about this:
It uses the aforementioned RenderScript framework and the code can be easily reused - check out the YuvToRgbConverter.kt class
according to their documentation, this code achieves " ~30 FPS # 640x480 on a Pixel 3 phone"
After switching to this code (especially the YUV to RGB conversion part) my framerate doubled! I am not quite reaching 30 FPS overall since I am doing a bit more things after capturing the image, but the speed-up is remarkable!
In our application, we need to transfer video, we are using Camera class to capture the buffer and send to destination,
I have set format is YV12 as a Camera parameter to receive the buffer,
for the 500X300 buffer, we receive buffer of 230400 bytes,
i want to know , is this expected buffer size ?
I believe the size would be
Y Plane = width * height = 500X300 = 150000
U Plane = width/2 * height/2 = = 37500
V Plane = width/2 * height/2 = = 37500
========
225000
========
Can anyone explain me, if i need to get stride values of each component, how can i get that
Is there any way to get it ?
I can show you how you can get int rgb[] from this:
public int[] decodeYUV420SP(byte[] yuv420sp, int width, int height) {
final int frameSize = width * height;
int rgb[] = new int[width * height];
for (int j = 0, yp = 0; j < height; j++) {
int uvp = frameSize + (j >> 1) * width, u = 0, v = 0;
for (int i = 0; i < width; i++, yp++) {
int y = (0xff & ((int) yuv420sp[yp])) - 16;
if (y < 0)
y = 0;
if ((i & 1) == 0) {
v = (0xff & yuv420sp[uvp++]) - 128;
u = (0xff & yuv420sp[uvp++]) - 128;
}
int y1192 = 1192 * y;
int r = (y1192 + 1634 * v);
int g = (y1192 - 833 * v - 400 * u);
int b = (y1192 + 2066 * u);
if (r < 0)
r = 0;
else if (r > 262143)
r = 262143;
if (g < 0)
g = 0;
else if (g > 262143)
g = 262143;
if (b < 0)
b = 0;
else if (b > 262143)
b = 262143;
rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000)
| ((g >> 2) & 0xff00) | ((b >> 10) & 0xff);
}
}
return rgb;
}
I guess Android document is already explained it:
http://developer.android.com/reference/android/graphics/ImageFormat.html#YV12
I think this is simple.
chekout YUVImage class from android. You can construct an YUV Image from byte[]data coming from camera preview.
You can write like this:
//width and height you get it from camera properties, image width and height of camera preview
YuvImage image=new YuvImage(data, ImageFormat.NV21, int width, int height, null);
byte[] newData = image.getYuvData();
//or if you want int format = image.getYuvFormat();
It's a quite old question, but I've struggled with the same issue for a few days. So I decided to write some comments to help others.
YV12 described in the Android developer site(here) seems not a kind of YV12 but IMC1. The page says that both of the y-stride and the uv-stride should be aligned in 16bytes.
And also this page says that:
For YV12, the image buffer that is received is not necessarily tightly
packed, as there may be padding at the end of each row of pixel data,
as described in YV12.
Based on the above comments, I calculated it using python command line:
>>> w = 500
>>> h = 300
>>> y_stride = (500 + 15) / 16 * 16.0
>>> y_stride
512.0
>>> y_size = y_stride * h
>>> y_size
153600.0
>>> uv_stride = (500 / 2 + 15) / 16 * 16.0
>>> uv_stride
256.0
>>> u_size = uv_stride * h / 2
>>> v_size = uv_stride * h / 2
>>> size = y_size + u_size + v_size
>>> size
230400.0
I am currently working on an Android application that processes camera frames retrieved from Camera.PreviewCallback.onPreviewFrame(). These frames are encoded in YUV420SP format and provided as a byte array.
I need to downsize the full frame and its contents, let's say by a factor of 2, from 640x480 px to 320x240. I guess, for downsizing the luminance part, I could just run a loop copying every second value from the byte[] frame to a new, smaller array, but what about the chrominance part? Does anyone know more about the structure of a YUV420SP frame?
Many thanks in advance!
Here is a code to get a half size RGBA image from yuv420sp bytes:
//byte[] data;
int frameSize = getFrameWidth() * getFrameHeight();
int[] rgba = new int[frameSize / 4];
for (int i = 0; i < getFrameHeight() / 2; i++)
for (int j = 0; j < getFrameWidth() / 2; j++) {
int y1 = (0xff & ((int) data[2 * i * getFrameWidth() + j * 2]));
int y2 = (0xff & ((int) data[2 * i * getFrameWidth() + j * 2 + 1]));
int y3 = (0xff & ((int) data[(2 * i + 1) * getFrameWidth() + j * 2]));
int y4 = (0xff & ((int) data[(2 * i + 1) * getFrameWidth() + j * 2 + 1]));
int y = (y1 + y2 + y3 + y4) / 4;
int u = (0xff & ((int) data[frameSize + i * getFrameWidth() + j * 2 + 0]));
int v = (0xff & ((int) data[frameSize + i * getFrameWidth() + j * 2 + 1]));
y = y < 16 ? 16 : y;
int r = Math.round(1.164f * (y - 16) + 1.596f * (v - 128));
int g = Math.round(1.164f * (y - 16) - 0.813f * (v - 128) - 0.391f * (u - 128));
int b = Math.round(1.164f * (y - 16) + 2.018f * (u - 128));
r = r < 0 ? 0 : (r > 255 ? 255 : r);
g = g < 0 ? 0 : (g > 255 ? 255 : g);
b = b < 0 ? 0 : (b > 255 ? 255 : b);
rgba[i * getFrameWidth() / 2 + j] = 0xff000000 + (b << 16) + (g << 8) + r;
}
Bitmap bmp = Bitmap.createBitmap(getFrameWidth()/2, getFrameHeight()/2, Bitmap.Config.ARGB_8888);
bmp.setPixels(rgba, 0/* offset */, getFrameWidth()/2 /* stride */, 0, 0, getFrameWidth()/2, getFrameHeight()/2);