can GD be used to change an image to black and white?

helz

can GD be used to change an image to black and white?
also ive noticed that with GD when ive used to to create thumbnails, some of the images look fine and others turn a yellow/brown colour in the thumbnail, even though they are all the same image format (.jpg)

planetsim

Weird that they are turn yellow. Id suggest stop using JPG images and start using PNG/Gif although PNG is probably the preferred (recommended by W3C ill check just to make sure).

Now for making images black and white. I dont think its possible, although you maybe able to use imagecolordeallocate may help.

helz

apparently GIF is a copyrighted format so GD doesnt support it, will try PNG

heres the place where it shows:
http://bowling.hellrazer.net/index.php?module=Photos

Weedpacket

The wonky colours are probably the result of GD Lib's rather lazy way of building a palette for the given truecolour image; the cure for that is generally to use the truecolour functions.

By "black and white" I guess you mean greyscale. That can be done by creating a new image with a greyscale palette in it (you don't need truecolour for greyscale!), and then copying the colour image into that.

	// We'll need the dimensions
	list($width,$height) = getimagesize('mycolourimage.jpg');

// And we'll need the image data itself!
$im = imagecreatefromjpeg("mycolourimage.jpg");

// Create a new image
$img = imagecreate($width,$height);
// Build its palette
for($i=0;$i<256;++$i)
	imagecolorallocate($img,$i,$i,$i);

// Copy the source image into the destination -
// colours will be shifted to fit the palette we just
// constructed
imagecopy($img,$im, 0,0,0,0, $width,$height);

// And I'm going to save the new image.
imagejpeg($img, 'mygreyimage.jpg');

helz

wow never knew it was that simple, having all my GD code being pulled from the internet, not really looked into it properly yet. so if the first 256 colours are for greyscale.
how would one create the truecolour palette? since its like 16million colours. bit big for a for() loop

Weedpacket

Originally posted by helz
how would one create the truecolour palette? since its like 16million colours. bit big for a for() loop

Truecolour doesn't use a palette. In a palette-based image each pixel stores a reference to the palette table which lists all the colours in the image; in a truecolour image each pixel stores the colour itself - so that in principle every pixel could be a different colour (up to 16-million-or-so!).

So saying that, there are separate functions for truecolour images - [man]imagecreatetruecolor[/man] in particular.

helz

ah, ill test that function now...
actually im not sure having never used GD before,
heres the code i have for creating a thumbnail of an original picture:

				header ("Content-type: image/jpeg"); 
		$src = imagecreatefromjpeg("$image"); 
		$im = imagecreate($newwidth,$newheight); 
		imagecopyresized($im,$src,0,0,0,0,$newwidth,$newheight,$width,$height); 
		imagejpeg($im); 
		imagedestroy($im);

what/where would i replace/add the imagecreatetruecolor

also does imagecreatetruecolor work for all image formats? (ie: the ones that GD supports)
GIF, JPG, WBMP, XBM, PNG

Weedpacket

Originally posted by helz
what/where would i replace/add the imagecreatetruecolor

You'd replace the "imagecreate". You might also want to use "imagecopyresampled" instead of "imagecopyresized", as the former uses a more sophisiticated interpolation technique.

also does imagecreatetruecolor work for all image formats? (ie: the ones that GD supports)
GIF, JPG, WBMP, XBM, PNG

GD doesn't support GIF (or if it does, it doesn't support truecolour) - good thing, too: PNG is a better format anyway. But then, GIF doesn't support truecolour either.

The formats it can write all support truecolour with the exception of WBMP, which is a bilevel format; so to write a WBMP all colours below a certain (user-specified) brightness are converted to black, and all the rest to white.

Reading palette-based images and using them in truecolour images is no problem, since GD Lib can look at the palette and find out what colour the pixel is supposed to be.

helz

oo educational,
well i replace to the function names with the better types, and voila, all looks and works great!!

so would you recommend png above jpg? or does it matter on what picture it is.

Thanks Weedpacket

Weedpacket

Originally posted by helz
so would you recommend png above jpg? or does it matter on what picture it is.

Yeah, it depends on the type of picture. PNG is designed as a replacement for GIF (better compression, better interlacing, truecolour support, alpha channel transparency, absence of legal restrictions, etc.etc.etc.), and is suitable for image that need to be pixel-perfect, and any deviations from that are unsightly or make the image harder to work with.

JPEGs are better for photos and naturalistic images where you don't mind pixels being a little bit off if it means the file is smaller.

helz

if it is designed as a replacement does that include animation?

Weedpacket

Originally posted by helz
if it is designed as a replacement does that include animation?

Not directly; it was decided early on that writing a single image format to handle both still and animated images was too much hassle for implementors, and instead MNG was developed (relevant links on the PNG page above). Some advantages to this, some disadvantages, some errors of judgement early on (for a while it was being worked on as though it was competing with MPEG, when all it needed was to be a bit better than animated GIF), but the practical upshot is that MNG is nowhere near so widely used yet. But the nice thing that's turned out is that, being a separate format, the sequence of frames can be either PNG format or JPEG format. Yes! animated JPEGs!

helz

wow, never heard of MNG
animated jpeg's seem like something to show off about!

will take a look around and see how things are done,
so would you say that the animation is already there?
or is it still in development?

do you have an idea of what programs support the MNG, and JNG

also do you know anything about TIF format?