WebP is an image format which is both lossy and lossless compression. Widely used in all Android app, including us. If you wish to get more detail about WebP, please check the following link:
Why WebP
We use WebP heavily inside the project not just because it save the network bandwidth but also cut down size for all image resources to save APK size.
But if you don’t pay attention to the bitmap size that it will become at Runtime, you may go into OOM error like us.
How does it happen
Stacktrace
When we look at the crash log, it will start from the inflating process:
and end up calling to getDrawable, which cause the system to allocate a bitmap for pixel data:
Suspect Image
Let’s take a look at the size again. Because the system will use ARGB_8888 to create a bitmap by default, we can divide the number by 4:
3688412 / 4 = 921603 = 960 * 960 |
The result shows the image size is 960. Luckily, there’s only one ImageView inside the XML file, so we quickly identify the image which causes OOM error.
Targeting image resource
Since the screenDensity of the crashed device is 320. We found the image inside drawable-xhdpi:
It’s a WebP with the size just the same as we expect, now we find the reason for the OOM.
Lesson learn
WebP can be pretty small in size but may be very large in bitmap at Runtime. The bitmap size of a WebP will depend on the size of the image before the transformation. Don’t create a WebP from a PNG that the size is larger than you need.
What’s more
If we look at the distribution on all OS version, you can see the crash more likely happens on OS version from 3 to 7:
The reason for this is because Google has changed the location to store bitmap. To be short, a bitmap will be stored inside the Dalvik heap, which is limited and mostly is very small; on the contrary, a bitmap will be placed inside the Native heap, which is expandable with a larger limit, sometimes the limit depends on the physical memory size.
With the difference above, you will more easily get OOM on Android 3 to 7, to check more detail about it, please refer to the official document:
If you curious about how this gonna influence the Bitmap Memory, please check: