Unforatanely what you want to do is not possible in Photoshop, this is called **local contrast normalization** and it is used for example in biomedical imaging to bring the image, or other type of signal, into a range that is more familiar or normal to the senses, hence the term **normalization**. Often, the motivation is to achieve consistency in dynamic range for a set of data, signals, or images to avoid mental distraction or fatigue. For example, a newspaper will strive to make all of the images in an issue share a similar range of grayscale. 

This problem is easily solved in the field of Computer Graphics, where you can find computer algorithms and specialized software that makes the process of grayscale conversion more friendly.