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PORgb to grayscale conversion with arm neon
 

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  1. PORgb to grayscale conversion with arm neon
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    <p>I´m trying to convert from rgb to grayscale efficiently, so I got a function from <a href="http://computer-vision-talks.com/2011/02/a-very-fast-bgra-to-grayscale-conversion-on-iphone/" rel="nofollow">here</a> where it explains how to convert from rgba to grayscale. Now I´m trying to do the same but with just rgb. I changed some things but it doesn´t seem to work well. I don´t know why, does anyone see my mistake?</p> <pre><code>void neon_asm_convert(uint8_t * __restrict dest, uint8_t * __restrict src, int numPixels) { __asm__ volatile( "lsr %2, %2, #3 \n" "# build the three constants: \n" "mov r4, #28 \n" // Blue channel multiplier "mov r5, #151 \n" // Green channel multiplier "mov r6, #77 \n" // Red channel multiplier "vdup.8 d4, r4 \n" "vdup.8 d5, r5 \n" "vdup.8 d6, r6 \n" "0: \n" "# load 8 pixels: \n" //RGBR "vld4.8 {d0-d3}, [%1]! \n" "# do the weight average: \n" "vmull.u8 q7, d0, d4 \n" "vmlal.u8 q7, d1, d5 \n" "vmlal.u8 q7, d2, d6 \n" "# shift and store: \n" "vshrn.u16 d7, q7, #8 \n" // Divide q3 by 256 and store in the d7 "vst1.8 {d7}, [%0]! \n" "subs %2, %2, #1 \n" // Decrement iteration count "# load 8 pixels: \n" "vld4.8 {d8-d11}, [%1]! \n" //Other GBRG "# do the weight average: \n" "vmull.u8 q7, d3, d4 \n" "vmlal.u8 q7, d8, d5 \n" "vmlal.u8 q7, d9, d6 \n" "# shift and store: \n" "vshrn.u16 d7, q7, #8 \n" // Divide q3 by 256 and store in the d7 "vst1.8 {d7}, [%0]! \n" "subs %2, %2, #1 \n" // Decrement iteration count "# load 8 pixels: \n" "vld4.8 {d0-d3}, [%1]! \n" "# do the weight average: \n" "vmull.u8 q7, d10, d4 \n" "vmlal.u8 q7, d11, d5 \n" "vmlal.u8 q7, d0, d6 \n" "# shift and store: \n" "vshrn.u16 d7, q7, #8 \n" // Divide q3 by 256 and store in the d7 "vst1.8 {d7}, [%0]! \n" "subs %2, %2, #1 \n" // Decrement iteration count "# do the weight average: \n" "vmull.u8 q7, d1, d4 \n" "vmlal.u8 q7, d2, d5 \n" "vmlal.u8 q7, d3, d6 \n" "# shift and store: \n" "vshrn.u16 d7, q7, #8 \n" // Divide q3 by 256 and store in the d7 "vst1.8 {d7}, [%0]! \n" "subs %2, %2, #1 \n" // Decrement iteration count "bne 0b \n" // Repeat unil iteration count is not zero : : "r"(dest), "r"(src), "r"(numPixels) : "r4", "r5", "r6" ); } </code></pre>
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    1. COnot well? what happens?
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    2. COThe image is not good transformed.
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    3. COScreenshots or anything?
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