image roi crop + convert to ncnn::Mat
+--------------+
| y | /-------/
| x +-------+ | +-------+|
| | roih |im_h => | roih
| +-roiw--+ | +-roiw--+/
| |
+-----im_w-----+
ncnn::Mat in = ncnn::Mat::from_pixels_roi(im.data, ncnn::Mat::PIXEL_RGB, im_w, im_h, x, y, roiw, roih);
For Android Application, it is :
ncnn::Mat in = ncnn::Mat::from_android_bitmap_roi(env, image, ncnn::Mat::PIXEL_RGBA2RGB, x, y, roiw, roih);
image roi crop + resize + convert to ncnn::Mat
+--------------+
| y | /----/
| x +-------+ | +----+|
| | roih |im_h => | target_h
| +-roiw--+ | | ||
| | +----+/
+-----im_w-----+ target_w
ncnn::Mat in = ncnn::Mat::from_pixels_roi_resize(im.data, ncnn::Mat::PIXEL_RGB, im_w, im_h, x, y, roiw, roih, target_w, target_h);
For Android Application, it is :
ncnn::Mat in = ncnn::Mat::from_android_bitmap_roi_resize(env, image, ncnn::Mat::PIXEL_RGBA2RGB, x, y, roiw, roih, target_w, target_h);
ncnn::Mat export image + offset paste
+--------------+
/-------/ | y |
+-------+| | x +-------+ |
| h| => | | h |im_h
+---w---+/ | +---w---+ |
| |
+-----im_w-----+
const unsigned char* data = im.data + (y * im_w + x) * 3;
out.to_pixels(data, ncnn::Mat::PIXEL_RGB, im_w * 3);
ncnn::Mat export image + resize + roi paste
+--------------+
/----/ | y |
+----+| | x +-------+ |
| h| => | | roih|im_h
| || | +-roiw--+ |
+-w--+/ | |
+-----im_w-----+
const unsigned char* data = im.data + (y * im_w + x) * 3;
out.to_pixels_resize(data, ncnn::Mat::PIXEL_RGB, roiw, roih, im_w * 3);
image roi crop + resize
+--------------+
| y |
| x +-------+ | +----+
| | roih|im_h => | target_h
| +-roiw--+ | | |
| | +----+
+-----im_w-----+ target_w
const unsigned char* data = im.data + (y * im_w + x) * 3;
ncnn::resize_bilinear_c3(data, roiw, roih, im_w * 3, outdata, target_w, target_h, target_w * 3);
image resize + offset paste
+--------------+
| y |
+----+ | x +-------+ |
| h => | | roih |im_h
| | | +-roiw--+ |
+-w--+ | |
+-----im_w-----+
unsigned char* outdata = im.data + (y * im_w + x) * 3;
ncnn::resize_bilinear_c3(data, w, h, w * 3, outdata, roiw, roih, im_w * 3);
image roi crop + resize + roi paste
+--------------+ +-----------------+
| y | | roiy |
| x +-------+ | |roix----------+ |
| | h |im_h => | | target_h|outim_h
| +---w---+ | | | | |
| | | +-target_w-+ |
+-----im_w-----+ +-----outim_w-----+
const unsigned char* data = im.data + (y * im_w + x) * 3;
unsigned char* outdata = outim.data + (roiy * outim_w + roix) * 3;
ncnn::resize_bilinear_c3(data, w, h, im_w * 3, outdata, target_w, target_h, outim_w * 3);
image roi crop + rotate
+--------------+
| y |
| x +-------+ | +---+
| | < < h |im_h => | ^ |w
| +---w---+ | | ^ |
| | +---+
+-----im_w-----+ h
const unsigned char* data = im.data + (y * im_w + x) * 3;
ncnn::kanna_rotate_c3(data, w, h, im_w * 3, outdata, h, w, h * 3, 6);
image rotate + offset paste
+--------------+
| y |
+---+ | x +-------+ |
| ^ |h => | | < < w |im_h
| ^ | | +---h---+ |
+---+ | |
w +-----im_w-----+
unsigned char* outdata = im.data + (y * im_w + x) * 3;
ncnn::kanna_rotate_c3(data, w, h, w * 3, outdata, h, w, im_w * 3, 7);
image roi crop + rotate + roi paste
+--------------+ +-----------------+
| y | | roiy |
| x +-------+ | | roix +---+ |
| | < < h |im_h => | | ^ w |outim_h
| +---w---+ | | | ^ | |
| | | +-h-+ |
+-----im_w-----+ +-----outim_w-----+
const unsigned char* data = im.data + (y * im_w + x) * 3;
unsigned char* outdata = outim.data + (roiy * outim_w + roix) * 3;
ncnn::kanna_rotate_c3(data, w, h, im_w * 3, outdata, h, w, outim_w * 3, 6);
Source: docs/how-to-use-and-FAQ/efficient-roi-resize-rotate.md