Re: [avr-chat] Storing B&W bitmap images into Flash : file format suggestion ?

[Dustin Lang]

Some pointers:

-reading files: try fopen(), fread(); see "man fopen" on a linux box.

-image format: have a look at the "netpbm" toolkit.  It is very 
useful.  The "pbm" format may be useful for you.  For example, if your 
image is a black-and-white jpeg:

jpegtopnm bw.jpg | pgmtopbm > bw.pbm

The "bw.pbm" file has a short header followed by (8 pixels per byte) raw 
pixels.

This command:

od -t x1 bw.pbm

writes out the "bw.pbm" file as hex values.

If you do this:

od -t x1 bw.pbm | sed 's/  /,/g'

you can replace the spaces with commas and have something that you can 
copy-n-paste, with a bit of editing, into your C code.

cheers,
dstn.


On Wed, 13 Jan 2010, Vincent Trouilliez wrote:

> On Wed, 13 Jan 2010 10:56:03 +1030
> "Daniel O'Connor" <address@hidden> wrote:
>
> > Starting to sound like too much work IMO :)
>
> Yeah, I think I will just write my own little C programme to convert
> the picture into a C array of bytes. I now fancy doing it regardless,
> just as a little exercise... and it's just cool to build his own tools
> I find ! I mean, can't be that complex, just need to figure out how to
> read a binary file on Linux.
>
> > FreeBSD comes with 'file2c'
> > http://svn.freebsd.org/viewvc/base/head/usr.bin/file2c/file2c.c?revision=200462&view=markup
>
> I guess this does what I stated above ? It must read a file fro the
> disk, but for the life ofd me I can't see any instruction/command
> related to reading/opening files in this piece of code.. I must be
> blind ?! :-/
> Anyway, I will just search for some Linux C tutorial (I assume the
> commands to handle files/disks are specific to Linux, so a Windows
> C tutorial won't do !...)
>
> > Also it only does RGBA which will cost you lots of RAM since you only
> > want B&W.
>
> Yeah we have already pointed this out I think ;-)
>
> > RLE is Run Length Encoding, a basic compression scheme
> > http://en.wikipedia.org/wiki/Run-length_encoding
>
> Thanks ! This Wikipedia thing is bloody useful isn't it !
> RLE yeah.. now I think of it, ISTR it was used in the "PCX" picture
> file format in Windows 3.1 a century ago LOL...
>
> I don't think it's suited to my project though... it would save me
> space, but there is too much decoding for the case at hand, and it
> would be too much work when displaying font digits. So I prefer an
> uncompressed format, where I can just dump my array of bits straight
> onto the LCD, to draw very fast, with maybe some shifting or masking
> or trivial things, but no arythmetic/calculations...
>
> I was suggested this utility off-list:
>
> http://www.dreamsware.info/
>
> It looks great, but I am not quite sure that it stuffs 8 pixels per
> byte, I fear it wastes a whole byte for each single B/W pixel... which I
> can't afford (I am using an ATmega32, I have space for one full screen
> picture or two (I don't need more anyway), but that's about it). I must
> absolutely pack 8 pixels per byte. The BMP format I tried the other day
> appears to do that, so it could be a good base for my utility program.
> I will keep searching a little bit for less "polluted" formats though,
> to simplify the work.
>
>
> Regards,
>
> --
> Vince
>
>
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