Bitmap 类如何与opencv的Mat类互转？

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Bitmap,mat类,opencv,图像,渲染

Bitmap 类如何与opencv的Mat类互转？

福昕知识库
2025-12-31

当业务场景需要将 PDF 文件渲染为位图，并基于该位图开展图像处理（如裁剪、滤波）或图像识别（如 OCR、目标检测）等后续操作时，通常需要将 Foxit PDF SDK 自带的Bitmap类型，转换为常用图像类库的位图格式（以主流的 OpenCV Mat类为例），以此降低跨库开发的适配成本，便捷对接后续业务流程。

以下是 Foxit PDF SDK Bitmap 与 OpenCV Mat 双向互转的完整示例(java版本)：


    private static Bitmap Mat2Bitmap(Mat mat) throws PDFException {
        if (mat.empty()) {
            throw new RuntimeException("Mat is empty");
        }

        int width = mat.cols();
        int height = mat.rows();
        int channels = mat.channels();

        Mat convertedMat = new Mat();
        if (channels == 3) {
            // OpenCV 默认是 BGR，转回 RGB
            Imgproc.cvtColor(mat, convertedMat, Imgproc.COLOR_BGR2RGB);
        } else if (channels == 4) {
            // OpenCV 是 BGRA，转回 RGBA
            Imgproc.cvtColor(mat, convertedMat, Imgproc.COLOR_BGRA2RGBA);
        } else if (channels == 1) {
            // 灰度图无需转换
            convertedMat = mat.clone();
        } else {
            //不支持的通道数
            throw new RuntimeException("Unsupported channels: " + channels);
        }
        int bpp = channels * 8; // 每个像素的位数
        int rowValidBytes = width * channels; // 每行有效像素字节数（无填充）
        int pitch = rowValidBytes;

        int bufferSize = pitch * height;
        byte[] buffer = new byte[bufferSize];
        for (int row = 0; row < height; row++) {
            byte[] rowData = new byte[rowValidBytes];
            convertedMat.get(row, 0, rowData);

            // 复制到缓冲区的对应行（包含填充字节）
            int bufferRowStart = row * pitch;
            System.arraycopy(rowData, 0, buffer, bufferRowStart, rowValidBytes);
        }
       Bitmap bitmap = new Bitmap(width, height, e_DIBArgb, buffer,pitch);// pitch, buffer);
        convertedMat.release();
        return bitmap;
    }


    public static Mat bitmapToMat(Bitmap bitmap) throws PDFException {
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        int bpp = bitmap.getBpp();
        int pitch = bitmap.getPitch();
        byte[] buffer = bitmap.getBuffer();

        if (buffer == null) {
            throw new RuntimeException("Bitmap buffer is null");
        }

        int matType;
        int channels;
        if (bpp == 8) {
            matType = CvType.CV_8UC1;
            channels = 1;
        } else if (bpp == 24) {
            matType = CvType.CV_8UC3;
            channels = 3;
        } else if (bpp == 32) {
            matType = CvType.CV_8UC4;
            channels = 4;
        } else {
            throw new RuntimeException("Unsupported BPP: " + bpp);
        }

        Mat mat = new Mat(height, width, matType);
        int rowValidBytes = width * channels;

        for (int row = 0; row < height; row++) {
            int bufferRowStart = row * pitch;
            byte[] rowData = new byte[rowValidBytes];
            System.arraycopy(buffer, bufferRowStart, rowData, 0, rowValidBytes);

            mat.put(row, 0, rowData);
        }

        if (bpp == 24) {
            Imgproc.cvtColor(mat, mat, Imgproc.COLOR_RGB2BGR);
        } else if (bpp == 32) {
            Imgproc.cvtColor(mat, mat, Imgproc.COLOR_RGBA2BGRA);
        }

        return mat.clone();
    }