Feature proposal - image difference with offset

[Nikolai Vorontsov]

Hello Ihar,

sometimes you need not only to calculate the summary difference between two images, but also get (visualize) this difference.

Here is a ready SSE2 code snippet for the following transform:

byte out[8] = word image[8] - word previousImage[8] + fixed_offset

The difference can be small or even negative, so a fixed offset value is added. All calculation is done in 16-bit unsigned word values, saturated back to 8-bit unsigned result.

__m128i ofs = _mm_set1_epi16(offset);
__m128i zero = _mm_set1_epi8(0);

for each 16 bytes in line:
__m128i v1a = _mm_loadu_si128(image_line);
__m128i v1b = _mm_unpacklo_epi8(v1a, zero); // 16-bit high and low parts
v1a = _mm_unpackhi_epi8(v1a, zero);

__m128i v2a = _mm_loadu_si128(previousImage_line); // Same for another image line
__m128i v2b = _mm_unpacklo_epi8(v2a, zero);
v2a = _mm_unpackhi_epi8(v2a, zero);

v1b = _mm_sub_epi16(_mm_add_epi16(v1b, ofs), v2b); // Add offset first, subtract ref.image
v1a = _mm_sub_epi16(_mm_add_epi16(v1a, ofs), v2a);

v1a = _mm_packus_epi16(v1b, v1a); // Contert to 8-bit with saturation

_mm_storeu_si128(result_line, v1a);

Feel free to use it if you decide to add that kind of algo to your lib.

Nikolai

[Yermalayeu Ihar]

Hello, Nikolai!

It would be better if you add this code yourself. Join to the development of Simd Library at GitHub. If you have the wish I will give more information how to do this.

Ihar.