Hello, Author of Data.Bitmap here. The issue is caused by the fact that Data.Bitmap does *not* support bmp files at all. This should be clear from the documentation. The functions you tried to used use their own file format, which a really very simple format; they are only added for simple experimentation. (again, this is explicit in the docs). The same documentation points to the stb-image [1] package, which supports loading of some common formats (png, jpg, bmp). In general, I suggest that with package-specific question, unless it is a widely used package, mail the maintainer directly; you have better chance to get an answer that way. Regards, Balazs [1] http://hackage.haskell.org/package/stb-image Hello,
I am using bitmap-0.2 [1] to load a Bitmap file [2]. However, the following sample GHCi session fails for me.
Prelude Data.Bitmap Data.Bitmap.Pure.File> readBitmap "b.bmp" :: IO (Bitmap Word8) *** Exception: Data/Bitmap/Internal.hs:(63,17)-(67,15): Non-exhaustive patterns in case
I downloaded the sources of bitmap-0.2 from Hackage and modified the relevant function by appending the last line.
decodeCType :: CInt -> PixelComponentType decodeCType k = case k of 1 -> PctWord8 2 -> PctWord16 3 -> PctWord32 4 -> PctFloat _ -> error $ "decodeCType: unexpected integer (" ++ show k ++ ")"
With this modification the same GHCi session given above results in the following error.
Prelude Data.Bitmap Data.Bitmap.Pure.File> readBitmap "b.bmp" :: IO (Bitmap Word8) *** Exception: decodeCType: unexpected integer (7077888)
I don't have any idea where 7077888 comes from. Am I doing something wrong? Is my bitmap corrupted in some way? The number 7077888 has no apparent significance except that it is a perfect cube [3]. So I guess this is not a problem with endianness.
In fact as far as I can tell `decodeCType` is only called on `(PixelComponent t => c_type t)` and `c_type t` only yields integer values in the (inclusive) range of 1 to 4. That is if I am not missing some orphaned instance.
Could anyone please enlighten me what is happening and if I am doing something wrong?
In case this is relevant: I am using bitmap-0.2 from Hackage with GHC 7.4.1 on a 3.2.20 kernel i686 architecture Linux.
Regards, Alexander Foremny
[1] http://hackage.haskell.org/package/bitmap [2] https://www.dropbox.com/s/pyutvni9vx6f6mo/b.bmp [3] http://www.wolframalpha.com/input/?i=7077888