Re: [GD-DEVEL] Question about importing data from memory

Hi Jeff,

On Nov 28, 2007 3:56 PM, Jeff Cunningham <[email protected]> wrote:
> Hi,
>
> I am processing some imagery that comes directly from sensors so that I
> end up with it in an NxM array of unsigned integers of rgb values (for
> example, array[0][0]=\xff0000 would be a red pixel in the upper-left
> corner). Some of this imagery wants to end up on web pages with text
> annotation, which is why I am looking at using the gd library.
> Currently, I save these images as bmp files using my own code, convert
> them to jpeg using imagemagick's convert utility, and they have no
> annotations.
>
> Is there a way to get the data from my arrays directly into a gdImage? I
> was looking through the API and could only find the function
> gdImageCreateFromGdPtr:
>
> http://www.libgd.org/OldImageCreation#gdImageCreateFromGdPtr.28int_size.2C_void_.2Adata.29_.28FUNCTION.29
>
> but I couldn't find any description of the format of a GdPtr. I could go
> to the source code, but in my experience when something isn't described
> in the API, its often not stable, so I don't want to get off on the
> wrong track.

You can see an example in the PHP sources. It may sound complex at a
first glance but the principle is relatively simple. It uses a custom
IO Ctx and pass it to the gdImageCreate*Ctx function. The source can
be read online here:

http://cvs.php.net/viewvc.cgi/php-src/ext/gd/gd.c?revision=1.382&view=markup

See the imagecreatefromstring function.

One function that will considerably ease this task is
gdImageCreateFromData, it is not yet implemented but it is planed for
2.1.x. This function let you create a GD image using your own buffer.

> I did take a look at a couple of the files like gdxpm.c for guidance,
> and there it appears that one creates a gdImage and populates it by
> creating a color table on the fly and writing indices instead of pixels.
> The problems I can see with this approach are that - unless duplicate
> color entries are allowed - there will be a significant overhead
> involved in searching the table for an existing color each time before
> creating a new one, which with Truecolor could be hugely inefficient.

You can have duplicate colors in a palette. Each palette entry is
independent from another. The amount of entries is limited to 256.
TrueColor images may be more efficient in your case.

>  I didn't see any related discussions in the list archives. How do
> people handle this kind of problem?

I can try to implement the basic features for the new
gdImageCreateFromData, it may ease your work and will give me some
early feedbacks :-)

Cheers,
--Pierre