NSImage batch conversion

HI, I've been trying to do a batch converter for images. The problem
is the memory is not being released properly. When the for ends the
memory is ok, but during the for it continues increasing. I have a
function with a for loop:
	for(count=0;count<cant;count++)
	{
		path=[datos objectAtIndex:count];
		save_name=[NSString stringWithFormat:
				@[EMAIL PROTECTED]
"image_%04d.jpg",count+1];
		output=[[batch_outdir stringValue]
stringByAppendingPathComponent:save_name];
		[self convert:path path_out:output format:NSJPEGFileType quality:
0.3];
	}

and then the conversion function

-(void)convert:(NSString*)path_in path_out:(NSString*)path_out format:
(NSBitmapImageFileType)type quality:(float)q
{
	NSDictionary *d=[NSDictionary dictionaryWithObject:
						[NSNumber numberWithFloat:q]
						forKey:NSImageCompressionFactor];
	NSImage	*tmp_img;
	NSBitmapImageRep *b;
	NSData *data;

	tmp_img=[[NSImage alloc] initWithContentsOfFile:path_in];
	b=[NSBitmapImageRep imageRepWithData:[tmp_img TIFFRepresentation]];
	[tmp_img release];

	data=[b representationUsingType:tipo properties:d];
	[data writeToFile:path_out atomically:TRUE];
}