Android相机能否限制拍摄图片的尺寸或文件大小？

问题背景 #

开发安卓应用时，系统相机拍摄的图片可达10MB（8000x6000像素），性能过剩，需要限制最大分辨率为4032x3024或最大文件大小3MB，现有代码如下：

private void dispatchTakePictureIntent() {
    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    // Ensure that there's a camera activity to handle the intent
    if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
        // Create the File where the photo should go
        File photoFile = null;
        try {
            photoFile = createImageFile();
        } catch (IOException ex) {
            // Error occurred while creating the File
            ...
        }
        // Continue only if the File was successfully created
        if (photoFile != null) {
            Uri photoURI = FileProvider.getUriForFile(this,
                                                  "com.example.android.fileprovider",
                                                  photoFile);
            takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
            startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
        }
    }
}

一、尝试直接限制拍摄分辨率（4032x3024） #

通过给相机Intent添加分辨率相关参数，可以尝试让系统相机直接输出指定尺寸的图片，但不同安卓厂商的系统相机对这些参数的支持不一致，部分厂商可能会忽略设置：

修改dispatchTakePictureIntent方法，添加分辨率参数：

private void dispatchTakePictureIntent() {
    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
        File photoFile = null;
        try {
            photoFile = createImageFile();
        } catch (IOException ex) {
            // 处理文件创建异常
        }
        if (photoFile != null) {
            Uri photoURI = FileProvider.getUriForFile(this,
                                                  "com.example.android.fileprovider",
                                                  photoFile);
            takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
            
            // 添加分辨率限制参数
            takePictureIntent.putExtra("outputX", 4032);
            takePictureIntent.putExtra("outputY", 3024);
            takePictureIntent.putExtra("aspectX", 4);
            takePictureIntent.putExtra("aspectY", 3);
            
            startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
        }
    }
}

如果系统相机不支持上述参数，这种方法会失效，此时需要在拍摄完成后对图片进行压缩处理。

二、拍摄后压缩图片（保证分辨率/文件大小达标） #

由于系统相机的兼容性问题，更可靠的方式是拍摄完成后，对图片进行压缩处理，同时满足分辨率和文件大小要求：

1. 工具类实现压缩逻辑

public class ImageCompressor {

    // 按分辨率压缩图片到指定尺寸以内
    public static Bitmap compressByResolution(String imagePath, int maxWidth, int maxHeight) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(imagePath, options);
        
        options.inSampleSize = calculateInSampleSize(options, maxWidth, maxHeight);
        options.inJustDecodeBounds = false;
        
        return BitmapFactory.decodeFile(imagePath, options);
    }

    // 计算图片采样率，避免内存溢出
    private static int calculateInSampleSize(BitmapFactory.Options options, int maxWidth, int maxHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > maxHeight || width > maxWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            while ((halfHeight / inSampleSize) >= maxHeight && (halfWidth / inSampleSize) >= maxWidth) {
                inSampleSize *= 2;
            }
        }
        return inSampleSize;
    }

    // 按文件大小压缩，直到文件小于目标大小（单位：KB）
    public static File compressByFileSize(Bitmap bitmap, String outputPath, int targetSizeKB) {
        File outputFile = new File(outputPath);
        int quality = 100;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos);

        while (baos.toByteArray().length / 1024 > targetSizeKB && quality > 0) {
            baos.reset();
            quality -= 10;
            bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos);
        }

        try {
            FileOutputStream fos = new FileOutputStream(outputFile);
            fos.write(baos.toByteArray());
            fos.flush();
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return outputFile;
    }
}

2. 在拍摄完成后调用压缩

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
        // 获取拍摄后图片的路径（需自行实现getImagePathFromUri方法）
        String imagePath = getImagePathFromUri(photoURI);
        
        // 先按分辨率压缩到4032x3024
        Bitmap compressedBitmap = ImageCompressor.compressByResolution(imagePath, 4032, 3024);
        // 再压缩到3MB以内（3*1024=3072KB）
        File finalFile = ImageCompressor.compressByFileSize(compressedBitmap, getCompressedImagePath(), 3072);
        
        // 使用finalFile进行后续业务处理
    }
}

三、注意事项 #

• 系统相机的ACTION_IMAGE_CAPTURE参数兼容性差，依赖厂商实现，拍摄后压缩是更可靠的方案
• 压缩图片时要注意读取Exif信息修正图片方向（部分相机拍摄的图片会有旋转角度）
• 处理大图片时要注意内存溢出问题，务必使用BitmapFactory.Options进行采样加载

内容的提问来源于stack exchange，提问作者JavaSheriff