CODEWITHSUNDEEP
c++libjpeg
Anthony
Anthony

Reputation: 7828

libJpeg garbled read

I'm using the example for the most part and it does create an image it's just garbled:

unsigned char* readJpeg(JNIEnv* env, libraw_processed_image_t *raw)
{
    // http://sourceforge.net/p/libjpeg-turbo/code/HEAD/tree/trunk/example.c#l109
    // http://stackoverflow.com/questions/5616216/need-help-in-reading-jpeg-file-using-libjpeg

    struct jpeg_decompress_struct cinfo;
    struct jpeg_error_mgr jerr;
    int row_stride;     /* physical row width in output buffer */

    cinfo.err = jpeg_std_error(&jerr);

    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(&cinfo);


    /* Step 2: specify data source (eg, a file) */
    jpeg_mem_src(&cinfo, raw->data, raw->data_size);

    /* Step 3: read file parameters with jpeg_read_header() */
    (void) jpeg_read_header(&cinfo, TRUE);

    /* Step 4: set parameters for decompression */

    /* In this example, we don't need to change any of the defaults set by
    * jpeg_read_header(), so we do nothing here.
    */

    /* Step 5: Start decompressor */

    (void) jpeg_start_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
    * with the stdio data source.
    */

    /* We may need to do some setup of our own at this point before reading
    * the data.  After jpeg_start_decompress() we have the correct scaled
    * output image dimensions available, as well as the output colormap
    * if we asked for color quantization.
    * In this example, we need to make an output work buffer of the right size.
    */
    /* JSAMPLEs per row in output buffer */
    row_stride = cinfo.output_width * cinfo.output_components;
    JSAMPROW rowData;
    unsigned char* imageData = new unsigned char[cinfo.output_height * row_stride];
    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */

    /* Here we use the library's state variable cinfo.output_scanline as the
    * loop counter, so that we don't have to keep track ourselves.
    */
    __android_log_write(ANDROID_LOG_INFO, "JNI", "Made it to read lines");
    int row = 0;
    while (cinfo.output_scanline < cinfo.output_height)
    {
        rowData = imageData + (row * row_stride);
        jpeg_read_scanlines(&cinfo, &rowData, 1);
        ++row;
    }

    /* Step 7: Finish decompression */

    (void) jpeg_finish_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
    * with the stdio data source.
    */

    /* Step 8: Release JPEG decompression object */

    /* This is an important step since it will release a good deal of memory. */
    jpeg_destroy_decompress(&cinfo);

    /* At this point you may want to check to see whether any corrupt-data
    * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
    */

    /* And we're done! */
    return imageData;
}

The image I'm reading loads fine in existing readers. I'm guessing I'm missing some sort of decompress setting, though I though it would be getting those from the header.

Garbled Image

Upvotes: 1

Views: 565

Answers (1)

madrag
madrag

Reputation: 1771

I faced similar problem but then later figured out that you have to align the RGB array to 8 byte boundary. check http://atlc.sourceforge.net/bmp.html#_toc381201083

Upvotes: 1

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