Bitmap in Android: Size of resources for displaying as 50dp

Question

I have a PNG image that I want to display in my application.

In the layout file (.xml) I set the width and height to 50dp (density-independent). But what should be the size of my resource(.png) files?

I thought about this (calculation based on density ratios):

• ldpi resource: 38
• mdpi resource: 50 (base)
• hdpi resource: 75
• xhdpi resource: 100

Or is one png file in "/res/drawables" enough that is 50px wide?

Answer 1

You will have to create 4 images. mdpi will be the baseline, meaning mdpi is 100%. Others follow this formula:

Place each image in the proper resource folder, drawable-ldpi , drawable-mdpi , drawable-hdpi , drawable-xhdpi . Android will choose the proper drawable depending on the current device.

Then, in your layout simply wrap_content your width and height, there is no need to specify any fixed size:

<ImageView
    android:src="@drawable/my_image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>

Answer 2

It's not enough to have just one image. You have to put a different image in each resource folders ( drawables-ldpi , drawables-mdpi , drawables-hdpi and drawables-xhdpi ).

Please note that 50dp is not equal with 50px

You can make use of this formula:

px = dp * (dpi / 160)

You can find other useful tips here .