如何在Android上以字节格式降低图像的质量？ [英] How do I reduce the quality of an image in byte format on Android?

问题描述

使用StackOverflow和其他有用网站的资源，我成功地创建了一个应用程序，可以上传相机应用程序在Android手机上拍摄的图像。唯一的麻烦是，手机我现在需要非常高品质的图片，导致上传的长等待时间。

Using resources from StackOverflow and other helpful websites, I was successful in creating an application that can upload an image taken by the camera application on an Android phone. The only trouble is, the phone I have right now takes very high-quality pictures, resulting in a long wait-time for uploads.

我阅读关于从jpeg转换图像到更低的速率（更小的尺寸或只是网络友好的大小），但我现在使用的代码现在保存捕获的图像作为一个字节（见下面的代码）。有没有任何方法来降低图像的质量，它的形式，或者我需要找到一种方式将其转换回jpeg，降低图像质量，然后将其放回字节形式？

I read about converting images from jpeg to a lower rate (smaller size or just web-friendly sizes), but the code I am using right now saves the captured image as a byte (see code below). Is there any way to reduce the quality of the image in the form that it is in, or do I need to find a way to convert it back to jpeg, reduce the image quality, and then place it back in byte form?

这是我使用的代码片段：

Here is the code snippet I'm working with:

    if (Intent.ACTION_SEND.equals(action)) {

        if (extras.containsKey(Intent.EXTRA_STREAM)) {
            try {

                // Get resource path from intent callee
                Uri uri = (Uri) extras.getParcelable(Intent.EXTRA_STREAM);

                // Query gallery for camera picture via
                // Android ContentResolver interface
                ContentResolver cr = getContentResolver();
                InputStream is = cr.openInputStream(uri);
                // Get binary bytes for encode
                byte[] data = getBytesFromFile(is);

                // base 64 encode for text transmission (HTTP)
                int flags = 1;
                byte[] encoded_data = Base64.encode(data, flags);
                // byte[] encoded_data = Base64.encodeBase64(data);
                String image_str = new String(encoded_data); // convert to
                                                                // string

                ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();

                nameValuePairs.add(new BasicNameValuePair("image",
                        image_str));

                HttpClient httpclient = new DefaultHttpClient();
                HttpPost httppost = new HttpPost(
                        "http://xxxxx.php");
                httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
                HttpResponse response = httpclient.execute(httppost);
                String the_string_response = convertResponseToString(response);
                Toast.makeText(UploadImage.this,
                        "Response " + the_string_response,
                        Toast.LENGTH_LONG).show();
            } catch (Exception e) {
                Toast.makeText(UploadImage.this, "ERROR " + e.getMessage(),
                        Toast.LENGTH_LONG).show();
                System.out.println("Error in http connection "
                        + e.toString());
            }
        }
    }
}

推荐答案

对于网络应用程序，你绝对不需要相机产生的5+ MP图像;图像分辨率是图像大小的主要因素，因此我建议您使用BitmapFactory类来产生一个下采样的位图。

For web apps, you definitely don't need the 5+ MP images that cameras produce; image resolution is the primary factor in image size, so I'd suggest you use the BitmapFactory class to produce a downsampled bitmap.

特别是看看BitmapFactory.decodeByteArray ，并传递一个BitmapFactory.Options参数，指示您想要一个下采样位图。

Particularly, look at BitmapFactory.decodeByteArray(), and pass it a BitmapFactory.Options parameter indicating you want a downsampled bitmap.

// your bitmap data
byte[] rawBytes = .......... ;

// downsample factor
options.inSampleSize = 4;  // downsample factor (16 pixels -> 1 pixel)

// Decode bitmap with inSampleSize set
return BitmapFactory.decodeByteArray(rawBytes, 0, rawBytes.length, options);

有关详情，请参阅有关显示位图的Android培训课程以及BitmapFactory ：

For more info, take a look at the Android Training lesson on displaying bitmaps efficiently and the reference for BitmapFactory:

http://developer.android。 com / training / displaying-bitmaps / index.html

http://developer.android.com/reference/android/graphics/BitmapFactory.html

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