Optimising image heavy applications
summary
Image decoding is CPU and memory heavy and UIImage often keeps decoded pixel buffers proportional to source resolution not view size, which explodes memory for large source images; decoding and caching cause fragmentation and can trigger compression or OOMs. Use Image I/O downsampling with CGImageSource with kCGImageSourceShouldCache=false and cgImageCreateThumbnailAtIndex to create thumbnails, run decoding asynchronously on a serial queue, and use collection view prefetching to avoid breaching the 16 ms frame budget.
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chapters (8)
- 0:00Start
- 5:58UIImage encapsulates this process
- 7:35However, decoding is expensive
- 12:16Downsampling - Step 1
- 15:25Dealing with CPU spikes due to downsampling
- 16:37Prefetching!
- 17:03Asynchronous downsampling serialQueue.async
- 17:50Additional Notes
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