Convert BMP file to PNG file in-memory

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Convert bitmap to PNG in-memory in C++ (win32)

I have a BMP file as a char* buffer. I want to convert this BMP file to a PNG file in-memory. I have tried it, and searched around a bit, but I couldn't find anything useful.

I can assume Windows XP or later, no .NET and C99.

Have you tried using [libpng](http://www.libpng.org/pub/png/libpng.html)? — Adam Rosenfield, Oct 31 '11 at 16:47
@Ash Burlaczenko: perhaps some encoding (LTR or RTL), and probably header differences. @Kerrek SB: I tried looking around in GDI+, but I got stuck on trying to deconfuscate the flattened C++ API and IIRC something with only being capable to an `IStream*`, which I have no idea to make. — orlp, Oct 31 '11 at 16:49
@The crocodile hunter: certainly __not__ a tool, but (not too heavy) library would be OK. — orlp, Oct 31 '11 at 16:50
@AdamRosenfield: I did look into it, but I wouldn't know how to use it (mostly converting the BMP into the libpng internal format). — orlp, Oct 31 '11 at 16:51
I already looked at that question, but I couldn't make a solution out of the answers. I get stuck on creating an `IStream*`. — orlp, Oct 31 '11 at 17:15
Use CreateStreamOnHGlobal(). Having an image in a *file format* resident in memory doesn't make much sense btw. — Hans Passant, Oct 31 '11 at 17:46

score 1 · Answer 1 · answered Oct 31 '11 at 17:10

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ImageMagick has a C API. I would assume, since it lets you perform various transformations on images, that those images are kept in memory, so you should be able to just load it as BMP and eventually save it as PNG.

answered Oct 31 '11 at 17:10

Vlad

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TheTechGuy · Answer 2 · 2011-10-31T17:07:11.920

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In memory means, you probably have to do it yourself. You have to understand the headers of both BMP and PNG files. After you successfully create the header, you can copy data but data is not stored in the same form in BMP and PNG so it is quite time consuming task.

Another way to do it, is use an external tool and call it from C code to do the conversion. However the in-memory problem will be in question.

edited Oct 31 '11 at 17:07

answered Oct 31 '11 at 16:56

TheTechGuy

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I was hoping there was a library that could do the conversion (partly). – orlp Oct 31 '11 at 16:58
I am not sure if this would help. http://libpng.org/pub/png/pngcode.html – TheTechGuy Oct 31 '11 at 17:02

Convert BMP file to PNG file in-memory

2 Answers2