Firebase 图片存储 - 缩略图

Question

Firebase 图片存储 - 缩略图

3

我在我的安卓应用中使用了Picasso，因此我可以从Firebase存储中检索图像URL到我的RecyclerView并显示它。现在，我想添加一个占位符，使用户在图片加载时能看到它。但是，我想像每个应用程序一样进行操作，首先将图像模糊处理成低分辨率缩略图，然后再显示原始图像（未模糊）。

我在Stack Overflow上搜索过，找到了很好的解决方案，例如制作两个Picasso语句，一个用于缩略图，然后通过onSuccess方法传递给我原始图像。但问题是，我需要2张图片，即原始图像的缩略图和完整的原始图像。

那么，如果我只上传了一张图片到服务器，如何检索到2张图片呢？下面是我在SO上发现的一点内容：

Transformation blurTransformation = new Transformation() {
    @Override
    public Bitmap transform(Bitmap source) {
        Bitmap blurred = Blur.fastblur(LiveImageView.this.context, source, 10);
        source.recycle();
        return blurred;
    }
 
    @Override
    public String key() {
        return "blur()";
    }
};
 
Picasso.with(context)
    .load(thumbUrl) // thumbnail url goes here
    .placeholder(R.drawable.placeholder)
    .resize(imageViewWidth, imageViewHeight)
    .transform(blurTransformation)
    .into(imageView, new Callback() {
        @Override
        public void onSuccess() {
            Picasso.with(context)
                    .load(url) // image url goes here
                    .resize(imageViewWidth, imageViewHeight)
                    .placeholder(imageView.getDrawable())
                    .into(imageView);
        }
 
        @Override
        public void onError() {
        }
    });

- user6099735

你尝试过通过XML将占位图添加到ImageView中（将占位图添加到drawable文件夹中），然后使用Picasso加载原始图像吗？或者如果要同时使用Picasso处理两种图像，则可以手动将占位图上传到Firebase存储，并从Firebase控制台获取下载URL。 - RamithDR

@RamithDR 是的，我可以在我的drawable中放置一个标准图像，但我不想显示一个标准图像，我想在完全加载之前显示我上传到服务器的模糊缩略图，看一下这个链接 https://abdelhadymu.files.wordpress.com/2015/02/whatsapp.png?w=634 - user6099735

请记住，上传到服务器的图片是随机的，并不是每次都相同的，这就是为什么我无法放置一个标准的占位符。 - user6099735

请查看下面我的答案。 - RamithDR

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- RamithDR · Accepted Answer

我知道了，得说这是个相当棘手的难题！

步骤1

首先，您需要创建一个模糊的Java类：

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Bitmap;
import android.os.Build;
import android.renderscript.Allocation;
import android.renderscript.Element;
import android.renderscript.RenderScript;
import android.renderscript.ScriptIntrinsicBlur;

/**
 * Created by RamithRD on 9/12/2016.
 */
public class Blur {

    @SuppressLint("NewApi")
    public static Bitmap fastblur(Context context, Bitmap sentBitmap, int radius) {

        if (Build.VERSION.SDK_INT > 16) {
            Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);

            final RenderScript rs = RenderScript.create(context);
            final Allocation input = Allocation.createFromBitmap(rs, sentBitmap, Allocation.MipmapControl.MIPMAP_NONE,
                    Allocation.USAGE_SCRIPT);
            final Allocation output = Allocation.createTyped(rs, input.getType());
            final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
            script.setRadius(radius /* e.g. 3.f */);
            script.setInput(input);
            script.forEach(output);
            output.copyTo(bitmap);
            return bitmap;
        }

        // Stack Blur v1.0 from
        // http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
        //
        // Java Author: Mario Klingemann <mario at quasimondo.com>
        // http://incubator.quasimondo.com
        // created Feburary 29, 2004
        // Android port : Yahel Bouaziz <yahel at kayenko.com>
        // http://www.kayenko.com
        // ported april 5th, 2012

        // This is a compromise between Gaussian Blur and Box blur
        // It creates much better looking blurs than Box Blur, but is
        // 7x faster than my Gaussian Blur implementation.
        //
        // I called it Stack Blur because this describes best how this
        // filter works internally: it creates a kind of moving stack
        // of colors whilst scanning through the image. Thereby it
        // just has to add one new block of color to the right side
        // of the stack and remove the leftmost color. The remaining
        // colors on the topmost layer of the stack are either added on
        // or reduced by one, depending on if they are on the right or
        // on the left side of the stack.
        //
        // If you are using this algorithm in your code please add
        // the following line:
        //
        // Stack Blur Algorithm by Mario Klingemann <mario@quasimondo.com>

        Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);

        if (radius < 1) {
            return (null);
        }

        int w = bitmap.getWidth();
        int h = bitmap.getHeight();

        int[] pix = new int[w * h];
        bitmap.getPixels(pix, 0, w, 0, 0, w, h);

        int wm = w - 1;
        int hm = h - 1;
        int wh = w * h;
        int div = radius + radius + 1;

        int r[] = new int[wh];
        int g[] = new int[wh];
        int b[] = new int[wh];
        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
        int vmin[] = new int[Math.max(w, h)];

        int divsum = (div + 1) >> 1;
        divsum *= divsum;
        int dv[] = new int[256 * divsum];
        for (i = 0; i < 256 * divsum; i++) {
            dv[i] = (i / divsum);
        }

        yw = yi = 0;

        int[][] stack = new int[div][3];
        int stackpointer;
        int stackstart;
        int[] sir;
        int rbs;
        int r1 = radius + 1;
        int routsum, goutsum, boutsum;
        int rinsum, ginsum, binsum;

        for (y = 0; y < h; y++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            for (i = -radius; i <= radius; i++) {
                p = pix[yi + Math.min(wm, Math.max(i, 0))];
                sir = stack[i + radius];
                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);
                rbs = r1 - Math.abs(i);
                rsum += sir[0] * rbs;
                gsum += sir[1] * rbs;
                bsum += sir[2] * rbs;
                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }
            }
            stackpointer = radius;

            for (x = 0; x < w; x++) {

                r[yi] = dv[rsum];
                g[yi] = dv[gsum];
                b[yi] = dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (y == 0) {
                    vmin[x] = Math.min(x + radius + 1, wm);
                }
                p = pix[yw + vmin[x]];

                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[(stackpointer) % div];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi++;
            }
            yw += w;
        }
        for (x = 0; x < w; x++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            yp = -radius * w;
            for (i = -radius; i <= radius; i++) {
                yi = Math.max(0, yp) + x;

                sir = stack[i + radius];

                sir[0] = r[yi];
                sir[1] = g[yi];
                sir[2] = b[yi];

                rbs = r1 - Math.abs(i);

                rsum += r[yi] * rbs;
                gsum += g[yi] * rbs;
                bsum += b[yi] * rbs;

                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }

                if (i < hm) {
                    yp += w;
                }
            }
            yi = x;
            stackpointer = radius;
            for (y = 0; y < h; y++) {
                // Preserve alpha channel: ( 0xff000000 & pix[yi] )
                pix[yi] = (0xff000000 & pix[yi]) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (x == 0) {
                    vmin[y] = Math.min(y + r1, hm) * w;
                }
                p = x + vmin[y];

                sir[0] = r[p];
                sir[1] = g[p];
                sir[2] = b[p];

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[stackpointer];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi += w;
            }
        }

        bitmap.setPixels(pix, 0, w, 0, 0, w, h);
        return (bitmap);
    }
}

模糊效果的代码来自：MichaelEvans - EtsyBlurExample

步骤 2

现在创建模糊转换：

Transformation blurTransformation = new Transformation() {
            @Override
            public Bitmap transform(Bitmap source) {
                Bitmap blurred = Blur.fastblur(MainActivity.this, source, 10);
                source.recycle();
                return blurred;
            }

            @Override
            public String key() {
                return "blur()";
            }
        };

第三步

使用Picasso加载图像：

Picasso.with(context)
    .load(url) // thumnail url goes here
    .transform(blurTransformation)
    .into(imageView, new Callback() {
        @Override
        public void onSuccess() {
            Picasso.with(context)
                    .load(url) // original image url goes here
                    .placeholder(imageView.getDrawable())
                    .into(imageView);
        }

        @Override
        public void onError() {
        }
    });

当我启动应用程序时，它首先显示原始图像但是模糊，然后显示原始图像。

为使其更加高效，我建议以下操作：将图像上传到Firebase存储时，您可以缩小图像的大小并将其与原始图像一起存储（可以使用Firebase数据库轻松完成，只需存储缩略图和原始图像的下载URL），并在通过Picasso加载图像时，可以先加载缩略图，然后再加载原始图像。

为了测试目的，我只使用了相同的URL。

有关重新调整图像大小的解答，请参考此处。

这是我的示例应用程序的GIF：

_{（来源：giphy.com）}