目錄
目錄
- JPEG圖片解碼
- 一：建立並初始化一個JPEG解碼物件（解碼物件是一個結構圖物件）
- 二：建立錯誤處理物件，並繫結解碼物件
- 三：開啟指定帶解碼的JPEG圖片
- 四：獲取待解碼圖片的圖片資訊，解析檔案頭。JPEG檔案中包含一些後設資料，如影像尺寸、顏色空間資訊等。解析檔案頭可以獲得這些後設資料，為後續處理做準備。
- 五：設定解碼引數。（可根據自身要求選擇對應引數，也可使用預設的引數）
- 六：開始解碼
- 七：呼叫迴圈從JPEG圖片中以行為單位進行解碼
- 八： 完成解碼
- 九：釋放解碼物件
- JPEG圖片編碼
JPEG圖片解碼
一：建立並初始化一個JPEG解碼物件（解碼物件是一個結構圖物件）
/* Step 1: allocate and initialize JPEG decompression object */
/* override error_exit. */
/* Now we can initialize the JPEG decompression object. */
jpeg_create_decompress(&cinfo);
二：建立錯誤處理物件，並繫結解碼物件
/* Step 2: We set up the normal JPEG error routines */
cinfo.err = jpeg_std_error(&jerr);
三：開啟指定帶解碼的JPEG圖片
/* Step 3: specify data source (eg, a file) */
jpeg_stdio_src(&cinfo, infile);
四：獲取待解碼圖片的圖片資訊，解析檔案頭。JPEG檔案中包含一些後設資料，如影像尺寸、顏色空間資訊等。解析檔案頭可以獲得這些後設資料，為後續處理做準備。
/* Step 4: read file parameters with jpeg_read_header() */
(void)jpeg_read_header(&cinfo, TRUE);
/* We can ignore the return value from jpeg_read_header since
* (a) suspension is not possible with the stdio data source, and
* (b) we passed TRUE to reject a tables-only JPEG file as an error.
* See libjpeg.txt for more info.
*/
五：設定解碼引數。（可根據自身要求選擇對應引數，也可使用預設的引數）
/* Step 5: 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.
*/
六：開始解碼
/* Step 6: 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; // 計算一行的大小
/* Make a one-row-high sample array that will go away when done with image */
buffer = calloc(1, row_stride);
七：呼叫迴圈從JPEG圖片中以行為單位進行解碼
/* Step 7: 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.
*/
int data = 0;
while (cinfo.output_scanline < cinfo.output_height)
{
/* jpeg_read_scanlines expects an array of pointers to scanlines.
* Here the array is only one element long, but you could ask for
* more than one scanline at a time if that's more convenient.
*/
(void)jpeg_read_scanlines(&cinfo, &buffer, 1); // 從上到下，從左到右 RGB RGB RGB RGB
for (int i = 0; i < cinfo.output_width; ++i) // 012 345
{
data |= buffer[3 * i] << 16; // R
data |= buffer[3 * i + 1] << 8; // G
data |= buffer[3 * i + 2]; // B
// 把畫素點寫入到LCD的指定位置
lcd_mp[800 * start_y + start_x + 800 * (cinfo.output_scanline - 1) + i] = data;
data = 0;
}
}
八： 完成解碼
/* Step 8: Finish decompression */
(void)jpeg_finish_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
九：釋放解碼物件
/* Step 9: Release JPEG decompression object */
/* This is an important step since it will release a good deal of memory. */
jpeg_destroy_decompress(&cinfo);
/* After finish_decompress, we can close the input file.
* Here we postpone it until after no more JPEG errors are possible,
* so as to simplify the setjmp error logic above. (Actually, I don't
* think that jpeg_destroy can do an error exit, but why assume anything...)
*/
fclose(infile);
/* 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 1;