Android 位图中 getPixel 和 getPixel 的更快替代方案？

Question

我正在为我的 Bitmap 使用方法 getPixel 和 setPixel，但它太慢了（getPixels 也是）。我想处理 Bitmap 的每个像素，然后创建另一个 Bitmap。如何通过 RenderScript 或使用 C++ 访问像素？我认为他们更快，但我不知道该怎么做。

这就是我使用 getPixel / setPixel:

所做的

  bitmap.getPixels(colorArray, 0, width, 0, 0, width, height);

    for (int x = 0; x < width; x++) {
        for (int y = 0; y < height; y++) {
            int g = Color.green(colorArray[y * width + x]);
            int b = Color.blue(colorArray[y * width + x]);
            int r = Color.red(colorArray[y * width + x]);
            //some color changes ....
            colorArray[y * width + x] = Color.rgb(r, g, b);
            returnBitmap.setPixel(x, y, colorArray[y * width + x]);
        }
    }

谢谢！

Answer 1

使用getPixels()获取所有像素，修改byte[]中的值，然后调用setPixels()一次存储所有像素。在每个像素上调用 setPixel() 的开销会降低您的性能。

如果仍然不够快，您可以将数组传递给 NDK 函数。

如果您正在对相机图像进行实时处理，则可以获得 even fancier。

Answer 2

我找到了这个 ColorMatrix 示例

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.graphics;

import com.example.android.apis.R;

import android.app.Activity;
import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;

public class ColorMatrixSample extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }

    private static class SampleView extends View {
        private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        private ColorMatrix mCM = new ColorMatrix();
        private Bitmap mBitmap;
        private float mSaturation;
        private float mAngle;

        public SampleView(Context context) {
            super(context);

            mBitmap = BitmapFactory.decodeResource(context.getResources(),
                                                   R.drawable.balloons);
        }

        private static void setTranslate(ColorMatrix cm, float dr, float dg,
                                         float db, float da) {
            cm.set(new float[] {
                   2, 0, 0, 0, dr,
                   0, 2, 0, 0, dg,
                   0, 0, 2, 0, db,
                   0, 0, 0, 1, da });
        }

        private static void setContrast(ColorMatrix cm, float contrast) {
            float scale = contrast + 1.f;
               float translate = (-.5f * scale + .5f) * 255.f;
            cm.set(new float[] {
                   scale, 0, 0, 0, translate,
                   0, scale, 0, 0, translate,
                   0, 0, scale, 0, translate,
                   0, 0, 0, 1, 0 });
        }

        private static void setContrastTranslateOnly(ColorMatrix cm, float contrast) {
            float scale = contrast + 1.f;
               float translate = (-.5f * scale + .5f) * 255.f;
            cm.set(new float[] {
                   1, 0, 0, 0, translate,
                   0, 1, 0, 0, translate,
                   0, 0, 1, 0, translate,
                   0, 0, 0, 1, 0 });
        }

        private static void setContrastScaleOnly(ColorMatrix cm, float contrast) {
            float scale = contrast + 1.f;
               float translate = (-.5f * scale + .5f) * 255.f;
            cm.set(new float[] {
                   scale, 0, 0, 0, 0,
                   0, scale, 0, 0, 0,
                   0, 0, scale, 0, 0,
                   0, 0, 0, 1, 0 });
        }

        @Override protected void onDraw(Canvas canvas) {
            Paint paint = mPaint;
            float x = 20;
            float y = 20;

            canvas.drawColor(Color.WHITE);

            paint.setColorFilter(null);
            canvas.drawBitmap(mBitmap, x, y, paint);

            ColorMatrix cm = new ColorMatrix();

            mAngle += 2;
            if (mAngle > 180) {
                mAngle = 0;
            }

            //convert our animated angle [-180...180] to a contrast value of [-1..1]
            float contrast = mAngle / 180.f;

            setContrast(cm, contrast);
            paint.setColorFilter(new ColorMatrixColorFilter(cm));
            canvas.drawBitmap(mBitmap, x + mBitmap.getWidth() + 10, y, paint);

            setContrastScaleOnly(cm, contrast);
            paint.setColorFilter(new ColorMatrixColorFilter(cm));
            canvas.drawBitmap(mBitmap, x, y + mBitmap.getHeight() + 10, paint);

            setContrastTranslateOnly(cm, contrast);
            paint.setColorFilter(new ColorMatrixColorFilter(cm));
            canvas.drawBitmap(mBitmap, x, y + 2*(mBitmap.getHeight() + 10),
                              paint);

            invalidate();
        }
    }
}

取自http://alvinalexander.com/java/jwarehouse/android-examples/platforms/android-6/samples/ApiDemos/src/com/example/android/apis/graphics/ColorMatrixSample.java.shtml

其他人在 SO 中也有很好的答案 Understanding the Use of ColorMatrix and ColorMatrixColorFilter to Modify a Drawable's Hue

Android 位图中 getPixel 和 getPixel 的更快替代方案？

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