Make ImageView have dark transparency

Try this second imageview will set the transparent color. Adjust the height according to your need.

500000 - last 4 digits stands for black color and first two stands for alpha you want to set.

                      <RelativeLayout
                        android:layout_width="match_parent"
                        android:layout_height="match_parent">
        
                        <ImageView
                            android:id="@+id/rest_image"
                            android:layout_width="match_parent"
                            android:layout_height="150dp"
                            android:adjustViewBounds="true"
                            android:scaleType="centerCrop"
                            />
    
                          <ImageView 
                            android:layout_width="match_parent"
                            android:layout_height="150dp" 
                            android:background="#500000"
                            />
                    </RelativeLayout>

You can add foreground tint with tint mode.

Make sure you add alpha channel in your foreground color.

foreground="##AARRGGBB"

AA = alpha channel in HEX R,G,B = Red, Blue, Green.

<ImageView
            android:id="@+id/vidthumbnail"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:scaleType="centerCrop"
            android:foreground="#96222f3e"
            android:foregroundTintMode="src_atop"/>

What you need is called tinting. Apply a tint to your ImageView:

<ImageView
    ...
    app:tint="#6F000000"
    />

Easiest/Fastest solution would be in XML

Add a second layer (can be a View, doesn't have to be an ImageView) on top of your ImageView, with the desired color/alpha. Show/Hide it when needed.

            <ImageView
                android:id="@+id/rest_image"
                android:layout_width="match_parent"
                android:layout_height="150dp"
                android:adjustViewBounds="true"
                android:scaleType="centerCrop"
                />

            <View
                android:id="@+id/overlay_image"
                android:layout_width="match_parent"
                android:layout_height="150dp"
                android:background=“@color/yourColorWithAlpha"
                />
        </RelativeLayout>