LabVIEW
Evaluate how red the pixels are in an image
Solved!
@Xiang00 wrote:
I have an RGB image and want to evaluate the redness of each pixel.
Most easiest way probably is to switch to CIE Lab model and check the distance between "pure red" and color of each pixel, lower values will be closer to Red, larger - far away, something like that:
And you can perform threshold to get a mask if needed:
VI is attached (LV2018).
@Xiang00 wrote:
Thank you for the suggestion! I will try to improve the code.
The image size is 3000x1000, and my CPU is the AMD Ryzen 7 5700U.
You're welcome!
I'm not sure how familiar you are with IMAQ, but if I attack this problem, I would wrap everything into a DLL. This would give you a huge improvement.
For example, first just check where we are with pure LabVIEW implementation. To check this I will upsample the original 640x400 image to 2560x1600, which is close to your image and benchmark it:
On my Intel Xeon W-2245 @ 3,90 GHz this will give me 3,2 seconds for 640x400 and 52,2 seconds for 2560x1600.
Now to get everything in DLL I will need first RGB to CIE Lab conversion. I will take the equations from OpenCV and with a little help of AI will get the following code:
// https://docs.opencv.org/3.1.0/de/d25/imgproc_color_conversions.html
inline void rgbToLab(uint8_t R, uint8_t G, uint8_t B, float* L_out, float* a_out, float* b_out) {
// Step 1: Normalize RGB values
double r = (double)R / 255.0;
double g = (double)G / 255.0;
double b = (double)B / 255.0;
// Step 2: Apply gamma correction if needed
//r = (r > 0.04045) ? pow((r + 0.055) / 1.055, 2.4) : r / 12.92;
//g = (g > 0.04045) ? pow((g + 0.055) / 1.055, 2.4) : g / 12.92;
//b = (b > 0.04045) ? pow((b + 0.055) / 1.055, 2.4) : b / 12.92;
// Convert to XYZ
double X = r * 0.412453 + g * 0.357580 + b * 0.180423;
double Y = r * 0.212671 + g * 0.715160 + b * 0.072169;
double Z = r * 0.019334 + g * 0.119193 + b * 0.950227;
// Step 3: Normalize for D65 illuminant
X /= 0.950456; // Reference white point D65
Y /= 1.000000;
Z /= 1.088754;
// Step 4: Convert to Lab
float L = (float)((Y > 0.008856) ? 116.0 * pow(Y, (1 / 3.0)) - 16.0 : 903.3 * Y);
X = (X > 0.008856) ? pow(X, (1 / 3.0)) : (X * (7.787) + (16.0 / 116.0));
Y = (Y > 0.008856) ? pow(Y, (1 / 3.0)) : (Y * (7.787) + (16.0 / 116.0));
Z = (Z > 0.008856) ? pow(Z, (1 / 3.0)) : (Z * (7.787) + (16.0 / 116.0));
*L_out = L * 2.55f; //To match LabVIEW's 8-bit images
*a_out = (float)(500.0 * (X - Y));
*b_out = (float)(200.0 * (Y - Z));
}
Now I will prepare DLL function. To stay prepared for multithreading I will add start/end parameters in assumption that I will split image to the stripes and handle these in parallel. Technically I will obtain RAW pointers to the pixels (you can use IMAQ GetImagePixelPtr, but this will require more DLLs inputs), then iterate over rows:
COLORMATCH_API int fnColorMatch(NIImageHandle src, NIImageHandle dst, TD1* color, int32_t start_line, int32_t end_line)
{
Image *ImgSrc, *ImgDst;
uint8_t *pLVImageRGB;
float* pLVImageDistance;
int LVWidth, LVHeight, x, y;
float distance;
uint8_t R, G, B;
float L_src, a_src, b_src, L_ref, a_ref, b_ref;
rgbToLab(color->RedValue, color->GreenValue, color->BlueValue, &L_ref, &a_ref, &b_ref);
if (!src || !dst) return ERR_NOT_IMAGE;
LV_SetThreadCore(1); //must be called prior to LV_LVDTToGRImage
LV_LVDTToGRImage(src, &ImgSrc);
LV_LVDTToGRImage(dst, &ImgDst);
if (!ImgSrc || !ImgDst) return ERR_NOT_IMAGE;
LVWidth = ((ImageInfo*)ImgSrc)->xRes;
LVHeight = ((ImageInfo*)ImgSrc)->yRes;
imaqSetImageSize(ImgDst, LVWidth, LVHeight);
int LVLineWidthsrc=((ImageInfo*)ImgSrc)->pixelsPerLine;
int LVLineWidthDst = ((ImageInfo*)ImgDst)->pixelsPerLine;
pLVImageRGB = (uint8_t*)((ImageInfo*)ImgSrc)->imageStart;
pLVImageDistance = (float*)((ImageInfo*)ImgDst)->imageStart;
if (!pLVImageRGB || !pLVImageDistance) return ERR_NOT_IMAGE;
if (end_line == 0) end_line = LVHeight;
pLVImageRGB += (start_line * LVLineWidthSrc) * 4;
pLVImageDistance += start_line * LVLineWidthDst;
for (y = start_line; y < end_line; y++) {
for (x = 0; x < LVWidth; x++) {
B = *(pLVImageRGB++);
G = *(pLVImageRGB++);
R = *(pLVImageRGB++);
rgbToLab(R, G, B, &L_src, &a_src, &b_src);
distance = (float)sqrt(SQR(L_src-L_ref) + SQR(a_src - a_ref) + SQR(b_src - b_ref));
*pLVImageDistance = distance;
pLVImageRGB++;
pLVImageDistance++;
}
pLVImageRGB += (LVLineWidthSrc - LVWidth) * 4;
pLVImageDistance += (LVLineWidthDst - LVWidth);
}
return 0;
}
Header file:
#ifdef COLORMATCH_EXPORTS
#define COLORMATCH_API extern "C" __declspec(dllexport)
#else
#define COLORMATCH_API __declspec(dllimport)
#endif
#include "include/nivision.h"
#include "include/extcode.h"
/* lv_prolog.h and lv_epilog.h set up the correct alignment for LabVIEW data. */
#include "include/lv_prolog.h"
/* Typedefs */
typedef struct {
uint8_t RedValue;
uint8_t GreenValue;
uint8_t BlueValue;
} TD1;
#include "include/lv_epilog.h"
#define SQR(x) ((x)*(x))
typedef uintptr_t NIImageHandle;
extern "C" int LV_SetThreadCore(int NumThreads);
extern "C" int LV_LVDTToGRImage(NIImageHandle niImageHandle, void* image);
COLORMATCH_API int fnColorMatch(NIImageHandle src, NIImageHandle dst, TD1* color, int32_t start_line, int32_t end_line);Now I will call this DLL function like this:
Now my execution time dropped for 2560x1600 from 52 seconds to 470 milliseconds, and for 640x400 from 3,2 s to 30 ms down, which means over 100x performance improvement.
But this not all, because my CPU have 8 physical cores, so I can use parallel computation like this:
Of course, I will not get pure 8x improvement, but execution time now: for 2560x1600 image is 85 milliseconds, and for 640x400 is 5 milliseconds only, which means roughly 600x imaprovement in comparizon to original LabVIEW code.
There are some areas for further improvement (around twice shall be possible), for example, we can use SIMD (AVX/AVX2) commands to compute multiple pixels with single commands, but this will require to use Intrinsics or Assembler, and usually required huge amount of time for programming. This technique was demonstrated here when I replaced IMAQ FlatField correction with AVX-based computation. Another possible way is to use highly optimized Intel Compiler, for example, if I will compile DLL with OneAPI, then the execution time will be 3 ms and 47 ms for small and large images (means over 1000x times speed improvement), but this will add additional dependencies to your project.
Summary:
Full source code downgraded to LV2018 (x64 only) including C source code and project for Visual Studio Professional 2022 (v.17.11.4) in the attachment, feel free to use it as "getting started".
@Andrey_Dmitriev wrote:
@Xiang00 wrote:
Thank you for the suggestion! I will try to improve the code.
The image size is 3000x1000, and my CPU is the AMD Ryzen 7 5700U.
You're welcome!
I'm not sure how familiar you are with IMAQ, but if I attack this problem, I would wrap everything into a DLL. This would give you a huge improvement.
For example, first just check where we are with pure LabVIEW implementation. To check this I will upsample the original 640x400 image to 2560x1600, which is close to your image and benchmark it:
On my Intel Xeon W-2245 @ 3,90 GHz this will give me 3,2 seconds for 640x400 and 52,2 seconds for 2560x1600.
Now to get everything in DLL I will need first RGB to CIE Lab conversion. I will take the equations from OpenCV and with a little help of AI will get the following code:
// https://docs.opencv.org/3.1.0/de/d25/imgproc_color_conversions.html inline void rgbToLab(uint8_t R, uint8_t G, uint8_t B, float* L_out, float* a_out, float* b_out) { // Step 1: Normalize RGB values double r = (double)R / 255.0; double g = (double)G / 255.0; double b = (double)B / 255.0; // Step 2: Apply gamma correction if needed //r = (r > 0.04045) ? pow((r + 0.055) / 1.055, 2.4) : r / 12.92; //g = (g > 0.04045) ? pow((g + 0.055) / 1.055, 2.4) : g / 12.92; //b = (b > 0.04045) ? pow((b + 0.055) / 1.055, 2.4) : b / 12.92; // Convert to XYZ double X = r * 0.412453 + g * 0.357580 + b * 0.180423; double Y = r * 0.212671 + g * 0.715160 + b * 0.072169; double Z = r * 0.019334 + g * 0.119193 + b * 0.950227; // Step 3: Normalize for D65 illuminant X /= 0.950456; // Reference white point D65 Y /= 1.000000; Z /= 1.088754; // Step 4: Convert to Lab float L = (float)((Y > 0.008856) ? 116.0 * pow(Y, (1 / 3.0)) - 16.0 : 903.3 * Y); X = (X > 0.008856) ? pow(X, (1 / 3.0)) : (X * (7.787) + (16.0 / 116.0)); Y = (Y > 0.008856) ? pow(Y, (1 / 3.0)) : (Y * (7.787) + (16.0 / 116.0)); Z = (Z > 0.008856) ? pow(Z, (1 / 3.0)) : (Z * (7.787) + (16.0 / 116.0)); *L_out = L * 2.55f; //To match LabVIEW's 8-bit images *a_out = (float)(500.0 * (X - Y)); *b_out = (float)(200.0 * (Y - Z)); }
Now I will prepare DLL function. To stay prepared for multithreading I will add start/end parameters in assumption that I will split image to the stripes and handle these in parallel. Technically I will obtain RAW pointers to the pixels (you can use IMAQ GetImagePixelPtr, but this will require more DLLs inputs), then iterate over rows:
COLORMATCH_API int fnColorMatch(NIImageHandle src, NIImageHandle dst, TD1* color, int32_t start_line, int32_t end_line) { Image *ImgSrc, *ImgDst; uint8_t *pLVImageRGB; float* pLVImageDistance; int LVWidth, LVHeight, x, y; float distance; uint8_t R, G, B; float L_src, a_src, b_src, L_ref, a_ref, b_ref; rgbToLab(color->RedValue, color->GreenValue, color->BlueValue, &L_ref, &a_ref, &b_ref); if (!src || !dst) return ERR_NOT_IMAGE; LV_SetThreadCore(1); //must be called prior to LV_LVDTToGRImage LV_LVDTToGRImage(src, &ImgSrc); LV_LVDTToGRImage(dst, &ImgDst); if (!ImgSrc || !ImgDst) return ERR_NOT_IMAGE; LVWidth = ((ImageInfo*)ImgSrc)->xRes; LVHeight = ((ImageInfo*)ImgSrc)->yRes; imaqSetImageSize(ImgDst, LVWidth, LVHeight); int LVLineWidthsrc=((ImageInfo*)ImgSrc)->pixelsPerLine; int LVLineWidthDst = ((ImageInfo*)ImgDst)->pixelsPerLine; pLVImageRGB = (uint8_t*)((ImageInfo*)ImgSrc)->imageStart; pLVImageDistance = (float*)((ImageInfo*)ImgDst)->imageStart; if (!pLVImageRGB || !pLVImageDistance) return ERR_NOT_IMAGE; if (end_line == 0) end_line = LVHeight; pLVImageRGB += (start_line * LVLineWidthSrc) * 4; pLVImageDistance += start_line * LVLineWidthDst; for (y = start_line; y < end_line; y++) { for (x = 0; x < LVWidth; x++) { B = *(pLVImageRGB++); G = *(pLVImageRGB++); R = *(pLVImageRGB++); rgbToLab(R, G, B, &L_src, &a_src, &b_src); distance = (float)sqrt(SQR(L_src-L_ref) + SQR(a_src - a_ref) + SQR(b_src - b_ref)); *pLVImageDistance = distance; pLVImageRGB++; pLVImageDistance++; } pLVImageRGB += (LVLineWidthSrc - LVWidth) * 4; pLVImageDistance += (LVLineWidthDst - LVWidth); } return 0; }Header file:
Spoiler#ifdef COLORMATCH_EXPORTS #define COLORMATCH_API extern "C" __declspec(dllexport) #else #define COLORMATCH_API __declspec(dllimport) #endif #include "include/nivision.h" #include "include/extcode.h" /* lv_prolog.h and lv_epilog.h set up the correct alignment for LabVIEW data. */ #include "include/lv_prolog.h" /* Typedefs */ typedef struct { uint8_t RedValue; uint8_t GreenValue; uint8_t BlueValue; } TD1; #include "include/lv_epilog.h" #define SQR(x) ((x)*(x)) typedef uintptr_t NIImageHandle; extern "C" int LV_SetThreadCore(int NumThreads); extern "C" int LV_LVDTToGRImage(NIImageHandle niImageHandle, void* image); COLORMATCH_API int fnColorMatch(NIImageHandle src, NIImageHandle dst, TD1* color, int32_t start_line, int32_t end_line);Now I will call this DLL function like this:
Now my execution time dropped for 2560x1600 from 52 seconds to 470 milliseconds, and for 640x400 from 3,2 s to 30 ms down, which means over 100x performance improvement.
But this not all, because my CPU have 8 physical cores, so I can use parallel computation like this:
Of course, I will not get pure 8x improvement, but execution time now: for 2560x1600 image is 85 milliseconds, and for 640x400 is 5 milliseconds only, which means roughly 600x imaprovement in comparizon to original LabVIEW code.
There are some areas for further improvement (around twice shall be possible), for example, we can use SIMD (AVX/AVX2) commands to compute multiple pixels with single commands, but this will require to use Intrinsics or Assembler, and usually required huge amount of time for programming. This technique was demonstrated here when I replaced IMAQ FlatField correction with AVX-based computation. Another possible way is to use highly optimized Intel Compiler, for example, if I will compile DLL with OneAPI, then the execution time will be 3 ms and 47 ms for small and large images (means over 1000x times speed improvement), but this will add additional dependencies to your project.
Summary:
Full source code downgraded to LV2018 (x64 only) including C source code and project for Visual Studio Professional 2022 (v.17.11.4) in the attachment, feel free to use it as "getting started".
I'm stunned.
@billko wrote:
I'm stunned.
Glad to see!
Well, in this particular case we can also use the fact that we have max 16777216 different colors and if we need to get color distance from "hard-coded red", then we can prepare LUT like this:
and then simply using this like that:
This will be much faster for sure (once LUT loaded into memory), but we will lost abilities to set color "on the fly", because this will require to re-compute LUT. But this approach can be also done in DLL, and we will be faster again (no so dramatically, but faster). On the other hand random read from 64MB LUT array can cause massive cache misses, but this can be improved by normalization to the range 0...255 and rounding to fit into one byte if high precision is not required... As usually — "pros" and "cons" everywhere.
