Do I Need Multiple Image Sizes (xxhdpi vs. xxxhdpi)?

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Apologies in advance for such a basic question, but this is my first app and I can't quite find a clear answer for my situation. All the images in my app are stored in the drawable folder, I'm NOT downloading any images from the internet. All the information I come across when it comes to multiple image sizes seems to refer to the occasion when the app is fetching images from the internet.

So currently most the images in my app are one size, customized for the largest size - xxxhdpi. However, I understand the app is doing some work to "shrink down" those images for the xxhdpi size screens.

I'm having second thoughts about this one size fits all approach. I'm thinking that perhaps the app doing the work to shrink the image down might take up extra memory and negatively impact performance. I've been looking at the Android Studio Profiler and I've been trying to understand the Graphics Process when I look at the Memory Graph.

More generally speaking, is there a benefit to having the smallest size images possible, even for the xxxhdpi? For example, does it hurt (memory wise or in some other aspect) to use a .png image when I could use a lower quality jpg? Again, just to super clear, this is just in the scenario when the app has all of its images in the drawable folder. My app has options where players can change the game background and other images so I want to be sure I'm optimizing how the images for best performance. Thanks.

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1 Answers

Memory. If you load a bitmap of x by y pixels, in memory that takes 4*x*y bytes. For a full screen image, you can expext that to be 4000*1000*4 or 16 MB. That's a good chunk of memory to a small device, which also tends to have less RAM. If instead it needed one at half the resolution, you would have 2000*500*4, or 4 MB.

Obviously this scales with size. The smaller your images, the less memory wasted. I wouldn't argue that you need to provide every size, but if you're using large images I'd provide more than one. Also, for anything that isn't incredibly complex (like icons) I'd consider vector images instead (although that's a CPU time vs memory tradeoff).

You mentioned png vs jpg. There's two things to consider there: apk size and image quality. JPG is smaller, so it will lead to a smaller apk size. PNG is lossless, so it will have higher quality (although whether that matters requires a human visual check- it matters less than you'd think on a lot of things). Interestingly it doesn't effect the amount of memory used at runtime, because both are held in the Bitmap object uncompressed.

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