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Sobel functions in IMGLIB are not relevant for HOG

Joey Lin
Intellectual 670 points

Dear supporter:

Our algorithm team currently requires the information of Histogram of Gradient (HOG) for image processing.  HOG is the combination result of Sobel X(H) , Sobel Y(V), Gradient Magnitude(GM), Gradient Orientation(GO), then Histogram generation.  We'd like to obtain simpler solution of GM thru an idea of absolute(Sobel X)+absolute(Sobel Y), which happens to be able to leverage TI API 

void IMG_sobel_3x3_8
(
const unsigned char *in, /* Input image data */
unsigned char *out, /* Output image data */
short cols, short rows /* Image dimensions */
)

Since our GM here is the combination of abs(Sobel X)+abs(Sobel Y), the addition should be over 255. 

However, as you may see the output data type (unsigned char) has clamped the data larger than 255

to 255

if (O > 255) O = 255; 

Would you please provide a solution by removing the clamping and outputting short data type instead.

We really appreciate your supports.

Joey


  • 0
    TI__Prodigy 160 points

    Joey, 

    Thank you for your post, we'll be working on this issue and let you know of the result as soon as it is possible. I apologize for the delay. 

    -Beverly 

  • 0 in reply to Beverly Wertz
    TI__Prodigy 160 points

    Joey, 

    We have been reviewing this function and wanted to make you fully aware of the maximum output value as well as confirm the output you were looking for. 

    For sobel_3x3_8, we wanted to confirm that you are looking for a function that has input data of unsigned char type and outputs data to a short. The limitation on the short data output utilizing the existing sobel_3x3_8 is that it has a maximum value of 32K.

    Let us know when possible and if you have any further input and/or questions. 

    -Beverly

  • 0 in reply to Beverly Wertz
    Intellectual 670 points

    Hi, Beverly:

    Your statement regarding to our request is correct, except the maximum output size of 32k seems to

     a bit confusing to us. The TI API, 

    IMG_sobel_3x3_8(

        const unsigned char **n,

        unsigned char *out, <==  we need short (data type)

        short cols,

        short rows

    ) 

    states the output size should be decided by input cols * (rows-2) -2, so that

    for (i = 0; i < cols*(rows-2) - 2; i++)
    {

    ....

    out[i + 1] = O;

    }

    Thanks a lot for your fully supports,

    Joey from Altek

  • 0 in reply to Joey Lin
    Intellectual 670 points

    Hi, Beverly:

    If you were talking about the "range" of sign short, the answer is yes to 32K.

    Sorry for the misunderstanding.

    Joey from Altek

  • 0 in reply to Joey Lin
    TI__Prodigy 160 points

    Joey, 

    Yes, the range of the output value is what I was referring to, sorry for the confusion. 

    -Beverly

    Joey Lin said:

    Hi, Beverly:

    If you were talking about the "range" of sign short, the answer is yes to 32K.

    Sorry for the misunderstanding.

    Joey from Altek

  • 0 in reply to Joey Lin
    TI__Prodigy 160 points

    1055.IMG_sobel_3x3_i8_c16.zip

    Joey, 

    Please find attached the modified sobel function: IMG_sobel_3x3_i8_c16  

    It will accept unsigned char input and output short values with a limitation of results in the range of 0-32K due to modifications made on the existing IMG_sobel_3x3_8 function. Test data is included to verify the function. Let us know if you have any questions. 

    -Beverly