core: add copyAt() for ROI operation #27318
Close https://github.com/opencv/opencv/issues/27320
Close https://github.com/opencv/opencv/issues/27298
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Add strict validation for encoding parameters #27621
Close https://github.com/opencv/opencv/issues/27557
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Imgcodec: gif: remove unnecessary warning #27169
Close https://github.com/opencv/opencv/issues/27168
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Fix heap buffer overflow and use after free in imgcodecs #27138
This fixes:
- https://g-issues.oss-fuzz.com/issues/405243132
- https://g-issues.oss-fuzz.com/issues/405456349
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GIF: Make sure to resize lzwExtraTable before each block #27081
This fixes https://g-issues.oss-fuzz.com/issues/403364362
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imgcodecs: gif: support animated gif without loop #26971Close#26970
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Imgcodecs: gif: support Disposal Method #26930
Close https://github.com/opencv/opencv/issues/26924
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imgcodecs:gif: support IMREAD_UNCHANGED and IMREAD_GRAYSCALE #26859Close#26858
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Performance tests for image encoders and decoders and code cleanup #26872
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Fix bugs in GIF decoding #26738
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this is related to #25691
i solved two bugs here:
1. the decoding setting:
according to [https://www.w3.org/Graphics/GIF/spec-gif89a.txt](https://www.w3.org/Graphics/GIF/spec-gif89a.txt)
```
DEFERRED CLEAR CODE IN LZW COMPRESSION
There has been confusion about where clear codes can be found in the
data stream. As the specification says, they may appear at anytime. There
is not a requirement to send a clear code when the string table is full.
It is the encoder's decision as to when the table should be cleared. When
the table is full, the encoder can chose to use the table as is, making no
changes to it until the encoder chooses to clear it. The encoder during
this time sends out codes that are of the maximum Code Size.
As we can see from the above, when the decoder's table is full, it must
not change the table until a clear code is received. The Code Size is that
of the maximum Code Size. Processing other than this is done normally.
Because of a large base of decoders that do not handle the decompression in
this manner, we ask developers of GIF encoding software to NOT implement
this feature until at least January 1991 and later if they see that their
particular market is not ready for it. This will give developers of GIF
decoding software time to implement this feature and to get it into the
hands of their clients before the decoders start "breaking" on the new
GIF's. It is not required that encoders change their software to take
advantage of the deferred clear code, but it is for decoders.
```
at first i didn't consider this case, thus leads to a bug discussed in #25691. the changes made in function lzwDecode() is aiming at solving this.
2. the fetch method of loopCount:
in the codes at https://github.com/opencv/opencv/blob/4.x/modules/imgcodecs/src/grfmt_gif.cpp#L410, if the branch is taken, 3 more bytes will be taken, leading to unpredictable behavior.
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[GSoC] Add GIF decode and encode for imgcodecs #25691
this is related to #24855
we add gif support for `imread`, `imreadmulti`, `imwrite` and `imwritemulti`
opencv_extra: https://github.com/opencv/opencv_extra/pull/1203
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Kumataro
Alexander Smorkalov
Suleyman TURKMEN
Vincent Rabaud
Super