Php thumbnail generation, insufficient memory solution

Php thumbnails are generated. if the memory is insufficient, php will be used to generate thumbnails. it is okay to operate KB + jpg images, but the png images around kb will show that the memory is exhausted. Allowedmemorysizeof8388608bytesexhausted
Use php to generate thumbnails,
It's okay to operate jpg images of KB +,
However, the png image around KB is displayed.
Memory exhausted,
Allowed memory size of 8388608 bytes exhausted (tried to allocate 3715200 bytes;
What is the cause,
How can this happen.

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How much memory you allocated to php

1. optimized memory
2. set memory_limit to be larger.
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Add ini_set ("memory_limit", "12 M") at the beginning of the row to check whether the problem can be solved.

If it cannot be solved, you need to optimize your code.
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