As I understand it, when I make a change in the tone curve in Adobe Photoshop (or Lightroom) and have selected the RGB Channel option, the following happens: For every pixel in the image, if any of the three color channels has the input value, it will be remapped to the output value. For example: In following image, every pixel has RGB value 0,70,0
If we do the following change in the curve, we haven't change the point that corresponds to 0, but we have changed the point that corresponds to 70 and remapped it to 137. So in every pixel in the image, in red, green and blue channels, if the value is 70, it wll be remapped to 137.
When we have selected only one of the three channels, the change will be applied only to this channel.
Is my understanding of the tone curve correct or something else happens? Are the tones in a colored image actually the 256 values of RGB color system?