On Mon, Jan 23, 2012 at 3:26 PM, Nicholas Cooper <nicho...@twpagency.com> wrote:
> On 23 January 2012 13:26, Matijn Woudt <tijn...@gmail.com> wrote:
>> On Mon, Jan 23, 2012 at 1:51 PM, Nicholas Cooper <nicho...@twpagency.com> 
>> wrote:
>>> Hi everyone,
>>> I've created an image in RGB from ImageMagick, it's 4 by 4 so I'm
>>> expecting 48 numbers (4*4*3). [width*height*(R,G,B)]
>>> When I read the file with PHP and unpack it I get between 330 and 333,
>>> I guess this difference is down to headers and end of file data.  Is
>>> there anyway to access only the useful image bits, those 48 numbers?
>>> Thank you,
>>> Nicholas Cooper
>> Hi,
>> The easiest way is probably using imagecolorat[1]. Just do a nested
>> for loop over x and y values, and call imagecolorat for each pixel.
>> Matijn
>> [1] www.php.net/imagecolorat
> Thank you that does the trick and gives the expected output.  I plan
> to be processing a large number of images and have always been wary of
> using the built in image functions for performance reasons.  So if
> there is any other solutions I'm welcome to them, or even if someone
> just wants to say that performance is not such an issue any more.

If the image you want to process is a simple bitmap (.bmp) file, then
you can easily parse it yourself. Wikipedia has a page on the file
format [1].

In short, fopen your file, fseek to 0x000A, read 4 bytes, and parse
them as little-endian (with unpack or so). fseek to that value, and
then you can read 4*4*3 bytes with fseek. That is your RGB data, if it
is in that format ofcourse. If you're not sure which format they are
you might need to parse more of the BMP header, but that's up to you.


[1] http://en.wikipedia.org/wiki/BMP_file_format

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