WIP: Undo horizontal prediction for each tile row in case of tiled tiff's #2878
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| @@ -712,6 +713,13 @@ private void DecodeTilesChunky<TPixel>( | |||
| { | |||
| Span<byte> uncompressedPixelRow = uncompressedPixelBufferSpan.Slice(uncompressedPixelBufferOffset, bytesToCopy); | |||
| tileBufferSpan.Slice(tileBufferOffset, bytesToCopy).CopyTo(uncompressedPixelRow); | |||
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| // Undo the horziontal predictor for each tile row. | |||
| if (this.Predictor == TiffPredictor.Horizontal) | |||
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@JimBobSquarePants I am not sure, if this is the best approach to undo the predictor here. I tried to do this in HorizontalPredictor.Undo(), but could not figure out a way without replicating the logic to iterate over the tiles in DecodeTilesChunky(). Maybe you have a better idea howto do this?
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So, are you writing the row, then undoing the write?
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It currently works like this:
- For each Tile: Decompress tile data
- For each row in tile: Undo horizontal predictor
- When done with all tiles: decode color
The horizontal predictor is used with lzw and deflate compression to achieve better compression. It assumes that neighboring pixel values do not change much and therefore only stores the difference between two consecutive pixels instead the actual pixel values.
Because it is tight to lzw and deflate compression, it feels to me this should be the concern of the decompressor and not be handled outside (which is the case for none tiled images).
I will try to gather more tiled image test cases for all the different color formats and then see if I can figure out a way how I can move the undoing of the predictor inside the uncompressing method.
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Ah, I understand.
I'm just trying to read through TiffLibrary and LibTiff.NET to see how it works there as a reference. I agree the decompressor feels like it should be responsible though.
…color type Rgb161616
…color type Rgba16161616
…color type Rgb323232
…color type Rgba with 32 bit for each channel
Prerequisites
Description
This PR fixes issue: #2877: The horizontal predictor needs to be reversed for each tile row in case of tiled images.
Note: This is still work in progress.