Some doubts related the resource (drawable) organization into an Android Studio project – Photoshop

I am very new in Android and I have the following doubts related how to handle images into my project.

I know that I have to put the images into the /res/drawable/ directory into my project.

To make order I have tryed to split up these images into differend subdirectory.

So for example I have created this subdirectory: /res/drawable/header/ that contains all the images related to the header of my application.

But when in the XML I do:

<ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:scaleType="fitStart"
        android:layout_height="250dp"
        android:src="@drawable/header/carbonara"/>

Android Studio give me an error on this line:

android:src="@drawable/header/carbonara"

that say to me that: ‘/’ is not a valid resource name character

So in Android I really can’t create structured and well organized subfolder for my images?

Another doubt is related to the different version fo the drawable folder.

I know that I can create a structure like this:

res
    drawable-hdpi
    drawable-ldpi
    drawable-mdpi
    .............
    .............
    .............

where each drawable* contain a specific version of the same images having different pixel density.

Using Android Studio can I automatically generate these folder starting from the drawable folder (containing my original images) or have I to create these folder manually and manually change the pixel density using something like Photoshop?