How to use ScriptIntrinsic3DLUT with a .cube file?

问题

first, I'm new to image processing in Android. I have a .cube file that was "Generated by Resolve" that is LUT_3D_SIZE 33. I'm trying to use android.support.v8.renderscript.ScriptIntrinsic3DLUT to apply the lookup table to process an image. I assume that I should use ScriptIntrinsic3DLUT and NOT android.support.v8.renderscript.ScriptIntrinsicLUT, correct?

I'm having problems finding sample code to do this so this is what I've pieced together so far. The issue I'm having is how to create an Allocation based on my .cube file?

...
final RenderScript renderScript = RenderScript.create(getApplicationContext());
final ScriptIntrinsic3DLUT scriptIntrinsic3DLUT = ScriptIntrinsic3DLUT.create(renderScript, Element.U8_4(renderScript));

// How to create an Allocation from .cube file?
//final Allocation allocationLut = Allocation.createXXX();

scriptIntrinsic3DLUT.setLUT(allocationLut);

Bitmap bitmapIn = selectedImage;
Bitmap bitmapOut = selectedImage.copy(bitmapIn.getConfig(),true);

Allocation aIn = Allocation.createFromBitmap(renderScript, bitmapIn);
Allocation aOut = Allocation.createTyped(renderScript, aIn.getType());

aOut.copyTo(bitmapOut);
imageView.setImageBitmap(bitmapOut);
...

Any thoughts?

回答1:

With a 3D LUT yes, you have to use the core framework version as there is no support library version of 3D LUT at this time. Your 3D LUT allocation would have to be created by parsing the file appropriately, there is no built in support for .cube files (or any other 3D LUT format).

回答2:

Parsing the .cube file

First, what you should do is to parse the .cube file. OpenColorIO shows how to do this in C++. It has some ways to parse the LUT files like .cube, .lut, etc. For example, FileFormatIridasCube.cpp shows how to process a .cube file.

You can easily get the size through LUT_3D_SIZE. I have contacted an image processing algorithm engineer. This is what he said:

Generally in the industry a 17^3 cube is considered preview, 33^3 normal and 65^3 for highest quality output.

Note that in a .cube file, we can get 3*LUT_3D_SIZE^3 floats. The key point is what to do with the float array. We cannot set this array to the cube in ScriptIntrinsic3DLUT with the Allocation. Before doing this we need to handle the float array.

Handle the data in .cube file

As we know, each RGB component is an 8-bit int if it is 8-bit depth. R is in the high 8-bit, G is in the middle, and B is in the low 8-bit. In this way, a 24-bit int can contain these three components at the same time.

In a .cube file, each data line contains 3 floats. Please note: the blue component goes first!!!

I get this conclusion from trial and error. (Or someone can give a more accurate explanation.)

Each float represents the coefficient of the component according to 255. Therefore, we need to calculate the real value with these three components:

int getRGBColorValue(float b, float g, float r) {
    int bcol = (int) (255 * clamp(b, 0.f, 1.f));
    int gcol = (int) (255 * clamp(g, 0.f, 1.f));
    int rcol = (int) (255 * clamp(r, 0.f, 1.f));
    return bcol | (gcol << 8) | (rcol << 16);
}

So we can get an integer from each data line, which contains 3 floats. And finally, we get the integer array, the length of which is LUT_3D_SIZE^3. This array is expected to be applied to the cube.

ScriptIntrinsic3DLUT

RsLutDemo shows how to apply ScriptIntrinsic3DLUT.

RenderScript mRs;
Bitmap mBitmap;
Bitmap mLutBitmap;
ScriptIntrinsic3DLUT mScriptlut;
Bitmap mOutputBitmap;
Allocation mAllocIn;
Allocation mAllocOut;
Allocation mAllocCube;
...
int redDim, greenDim, blueDim;
int[] lut;
if (mScriptlut == null) {
    mScriptlut = ScriptIntrinsic3DLUT.create(mRs, Element.U8_4(mRs));
}
if (mBitmap == null) {
    mBitmap = BitmapFactory.decodeResource(getResources(),
            R.drawable.bugs);

    mOutputBitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig());

    mAllocIn = Allocation.createFromBitmap(mRs, mBitmap);
    mAllocOut = Allocation.createFromBitmap(mRs, mOutputBitmap);
}
...
// get the expected lut[] from .cube file.
...
Type.Builder tb = new Type.Builder(mRs, Element.U8_4(mRs));
tb.setX(redDim).setY(greenDim).setZ(blueDim);
Type t = tb.create();
mAllocCube = Allocation.createTyped(mRs, t);
mAllocCube.copyFromUnchecked(lut);

mScriptlut.setLUT(mAllocCube);
mScriptlut.forEach(mAllocIn, mAllocOut);

mAllocOut.copyTo(mOutputBitmap);

Demo

I have finished a demo to show the work. You can view it on Github.
Thanks.

来源：https://stackoverflow.com/questions/25686572/how-to-use-scriptintrinsic3dlut-with-a-cube-file

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