【发布时间】：2013-10-23 13:20:28
【问题描述】：
我大部分时间都在使用该示例，它确实创建了一个只是乱码的图像：
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;
}
我正在阅读的图像在现有阅读器中加载良好。我猜我错过了某种解压缩设置，尽管我会从标题中获取这些设置。
【问题讨论】：
-
在我看来，行步长计算存在一些问题。可以调试看看没问题吗？在读取和显示功能中。
-
是的，这是有道理的，但我在整个程序中记录了输入并且它起作用了。另外只是为了检查我增加了宽度并得到了段错误，所以它是正确的尺寸。
-
实际上这似乎是正确的，在我看过的每张图像中，cinfo.output_width 似乎都偏离了 18 个像素......
-
更正，它因图像尺寸而异，在 18 像素范围内。高度也不对。基本上 cinfo 中的值由于某种原因是错误的......