Image Coder is just decoding part. Other part does not get effected and you (Image Decoder author) don't need to care about

@dreampiggy thanks i just wanted to make sure that once decoded/chached the image picked up from cache the next time does not need that decoding anymore ?
I mean is the cached image the decoded one or the "source" one.
Thanks again for everything

once decoded/chached the image picked up from cache the next time does not need that decoding anymore

Yes, for simple cases. Let me explain.

Assume your coder introduce a new image format we never see (like MYFORMAT)

SD's cache use memory and disk cache. For in-memory , we cache the UIImage (which means, your Image Coder returned decoded image object). So it's OK and we move this image object around.

For disk cache, since we need a way to serialize the UIImage into Data and write to disk, if you don't implements encodedData related encoding protocol API, normally we will cache the original downloaded data buffer into disk.

But some advanced feature like Transformer (like SDImageTintTransformer, which tint the original decoded image into another different one with color), this will fallback to use JPEG/PNG to serialize to the Data.

Because your coder don't support encoding, and we don't have the same data matching the new transformed UIImage, so this will use JPEG/PNG as backup solution. So in conclusion:

1. Download 1.MYFORMAT data, it stored into the disk cache for key https://1.MYFORMAT
2. The in-memory UIImage stored into memory cache for https://1.MYFORMAT
3. When use transformer, it generate a new cache key for https://1.MYFORMAT-transformer(Foobar), and store the transformed image to memory cache
4. It encode the transformed image into JPEG (instead of MYFORMAT) and stored to disk cache for key https://1.MYFORMAT-transformer(Foobar)

Can my explanation solve your question ?

@dreampiggy yes I think it does explains it perfectly! So if I implement the encodedData(which I can as the decoded image is a simple bitmap) it - should work best and only decode "once" then always use the cache "decoded" image.
Thanks a lot really love what you Ve created!

It's recommended to implements the encoding part. Most of image codec supports encoding. Which can make sure we always use your format instead of transcoding to another format like JPEG/PNG which may loss some information inside the image format, like EXIF