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Clarified the exact size of the HOG feature maps produced by

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extract_fhog_features().  Also fixed a minor bug where empty planar HOG feature
maps had 0 planes in them rather than 31 empty planes as the spec says they
should.
This commit is contained in:
Davis King 2014-07-19 12:09:55 -04:00
parent 98602c332a
commit 0eb725fc4f
3 changed files with 26 additions and 4 deletions
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9
dlib/image_transforms/fhog.h
View File

@ -637,7 +637,12 @@ namespace dlib
int filter_cols_padding = 1
)
{
return impl_fhog::impl_extract_fhog_features(img, hog, cell_size, filter_rows_padding, filter_cols_padding);
impl_fhog::impl_extract_fhog_features(img, hog, cell_size, filter_rows_padding, filter_cols_padding);
// If the image is too small then the above function outputs an empty feature map.
// But to make things very uniform in usage we require the output to still have the
// 31 planes (but they are just empty).
if (hog.size() == 0)
hog.resize(31);
}
template <
@ -653,7 +658,7 @@ namespace dlib
int filter_cols_padding = 1
)
{
return impl_fhog::impl_extract_fhog_features(img, hog, cell_size, filter_rows_padding, filter_cols_padding);
impl_fhog::impl_extract_fhog_features(img, hog, cell_size, filter_rows_padding, filter_cols_padding);
}
// ----------------------------------------------------------------------------------------

7
dlib/image_transforms/fhog_abstract.h
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@ -61,8 +61,11 @@ namespace dlib
area of a hog image (note that you should use the following planar version of
extract_fhog_features() instead of the interlaced version if you want to use
spatially_filter_image() on a hog image).
- #hog.nr() is approximately equal to img.nr()/cell_size + filter_rows_padding-1.
- #hog.nc() is approximately equal to img.nc()/cell_size + filter_cols_padding-1.
- #hog.nr() == max(round(img.nr()/(double)cell_size)-2,0) + filter_rows_padding-1.
- #hog.nc() == max(round(img.nc()/(double)cell_size)-2,0) + filter_cols_padding-1.
(i.e. Each output dimension is roughly 1/cell_size the original size but
there is a one cell_size border all around the image that is lost and then we
add on any additional padding that is requested.)
- for all valid r and c:
- #hog[r][c] == the FHOG vector describing the cell centered at the pixel location
fhog_to_image(point(c,r),cell_size,filter_rows_padding,filter_cols_padding) in img.

14
dlib/test/fhog.cpp
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@ -60,6 +60,10 @@ namespace
{
dlib::array<array2d<float> > hog;
extract_fhog_features(img, hog, sbin);
DLIB_TEST(hog.size() == 31);
DLIB_TEST_MSG(hog[0].nr() == max(static_cast<int>(img.nr()/(double)sbin+0.5)-2,0),
hog[0].nr() << " " << max(static_cast<int>(img.nr()/(double)sbin+0.5)-2,0));
DLIB_TEST(hog[0].nc() == max(static_cast<int>(img.nc()/(double)sbin+0.5)-2,0));
DLIB_TEST(hog.size() == 31);
for (long o = 0; o < (long)hog.size(); ++o)
@ -88,18 +92,28 @@ namespace
img.set_size(i,i);
assign_all_pixels(img, i);
extract_fhog_features(img, hog);
DLIB_TEST(hog.size() == 31);
DLIB_TEST(hog[0].nr() == max(static_cast<int>(img.nr()/8.0+0.5)-2,0));
DLIB_TEST(hog[0].nc() == max(static_cast<int>(img.nc()/8.0+0.5)-2,0));
}
for (int i = 1; i < 10; ++i)
{
img.set_size(i,i+1);
assign_all_pixels(img, i);
extract_fhog_features(img, hog);
DLIB_TEST(hog.size() == 31);
DLIB_TEST(hog[0].nr() == max(static_cast<int>(img.nr()/8.0+0.5)-2,0));
DLIB_TEST(hog[0].nc() == max(static_cast<int>(img.nc()/8.0+0.5)-2,0));
}
for (int i = 1; i < 10; ++i)
{
img.set_size(i+1,i);
assign_all_pixels(img, i);
extract_fhog_features(img, hog);
DLIB_TEST(hog.size() == 31);
DLIB_TEST(hog[0].nr() == max(static_cast<int>(img.nr()/8.0+0.5)-2,0));
DLIB_TEST(hog[0].nc() == max(static_cast<int>(img.nc()/8.0+0.5)-2,0));
}
}