Question: HSV values image pre-processing

[anandkoirala]

Hi @AlexeyAB Just few questions about the image pre-processing. HSV values for openCV is in range (0-180,0-255,0-255) while other programs may use (0-360, 0-1, 0-1). the pixel values are integers anyways. I am not good in C++ so digging into your source code I couldn't understand how YOLO is using the HSV values for Image preprocessing? is it a scalar multiplier of 0.1 and 1.5 to the pixel values (if yes that will result in floats)? or is it like addition of 10, 150 to the pixels? what is the HSV range used by YOLO? Thanks, Anand

[AlexeyAB]

@anandkoirala Hi,

In the Darknet image is represented as array of floats: https://github.com/AlexeyAB/darknet/blob/535353cdaad78714640c171fd797f281b0c49c28/src/image.h#L15-L16

• For RGB: r = [0, 1], g = [0, 1], b = [0, 1]
• For HSV: h = [0, 1], s = [0, 1], v = [0, 1]

So RGB and HSV always is normalized for range [0, 1]

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How HSV-data-augmentation works you can see here: if in the cfg file: hue=0.1, saturation=1.5, exposure=1.5 then dhue = [-0.1, 0.1], dsat = [1/1.5, 1.5], dexp = [1/1.5, 1.5]

• https://github.com/AlexeyAB/darknet/blob/535353cdaad78714640c171fd797f281b0c49c28/src/data.c#L738-L740
• https://github.com/AlexeyAB/darknet/blob/535353cdaad78714640c171fd797f281b0c49c28/src/http_stream.cpp#L265-L276