如何将图像从灰度格式更改为 RGB 格式

Question

I was working on research about computer vision, but I got stuck when following a paper that said he could convert Grayscale image into RGB image using Python.

The first image would be like this.

The output will be like this.

Is anyone could help me finish this problem?

Answer 1

I don't think this is possible, a grayscale image has just one channel (shades of gray), while, BGR (default color space in opencv, or BGRA if on mac)just like RGB has three channels (RED GREEN BLUE), you can convert it into grayscale using this formula:

Y = 0.299 R + 0.587 G + 0.114 B

where Y is the one channel of grayscale image. But you can't do the vice versa. Grayscale is basically just different shades of gray. You can't do the reverse. In RGB/BGR a pixel looks like this [R,G,B] which is somewhat like an array, whereas in grayscale it is just a single value. We often consider value < 100 as black in grayscale.

Image is often reprsented in form of an array ( np.array in case of python), and the thing is, in most of the arrays, you can't modify the dimensions. Like np.array has an attribute called shape which tells us about the dimensions of the array, or in an image think of it like resolution. Shape of a grayscale image looks like this (RESOLUTION-Y, RESOLUTION-X) , which means it's a 2d matrix/array and one pixel is represented by a single value, whereas in RGB/BGR, the shape looks like this, (RESOLUTION-Y, RESOLUTION-X, 3) , so it's a 3d array, where 3 is the number of channels.