iPhone ImageMagick Library - converting from batch file script to Objective-C using MagickWand API

Question

I've decided to use the following ImageMagick library for iPhone development:

https://github.com/marforic/imagemagick_lib_iphone

It works quite well. The sample project compiles just fine, but doesn't make any sense whatsoever.

Usually, I'll use the "convert.exe" that comes with ImageMagick for Windows to convert images via the command line. So I'll write a little batch file like the following:

@echo off

set SOURCE=image_to_convert.jpg

del result.jpg
del source_copy.jpg

convert.exe %SOURCE% -fill "#fff8f2" -colorize 100%% fill.jpg

copy %SOURCE% source_copy.jpg

convert.exe %SOURCE% -modulate 100,0,100 -|^
convert.exe - source_copy.jpg -compose overlay -composite -|^
convert.exe source_copy.jpg - -compose dissolve -define compose:args=37,100 -composite -|^
convert.exe - -modulate 100,70,100 +level 3.5%%,100%% -|^
convert.exe - -channel red -level 0%%,89%% +level 9%%,100%% -|^
convert.exe - -channel green +level 3.5%%,100%% -|^
convert.exe - -channel blue -level 0%%,93%% +level 4.7%%,100%% -|^
convert.exe - -brightness-contrast -5x3 -|^
convert.exe fill.jpg - -compose multiply -gravity center -composite -|^
convert.exe - -level 3.5%%,100%%,0.91 +level 2.7%%,100%% -|^
convert.exe - -channel red +level 3.5%%,100%% -|^
convert.exe - -channel green -level 0%%,87%% +level 1%%,100%% -|^
convert.exe - -channel blue -level 0%%,100%%,0.94 +level 7%%,100%% -|^
convert.exe - -brightness-contrast -1x0 final_converted_image.jpg

del source_copy.jpg
del fill.jpg

The problem is converting the above batch file to be used alongside that particular library.

- (void)convertImage {
    MagickWandGenesis();
    magick_wand = NewMagickWand();
    //UIImageJPEGRepresentation([imageViewButton imageForState:UIControlStateNormal], 90);
    NSData * dataObject = UIImagePNGRepresentation([UIImage imageNamed:@"iphone.png"]);
    MagickBooleanType status;
    status = MagickReadImageBlob(magick_wand, [dataObject bytes], [dataObject length]);
    if (status == MagickFalse) {
        ThrowWandException(magick_wand);
    }

    // Resize image.
    ImageInfo *imageInfo = AcquireImageInfo();
    ExceptionInfo *exceptionInfo = AcquireExceptionInfo();

    // Get image from bundle.
    char *input_image = strdup([[[NSBundle mainBundle] pathForResource:@"iphone" ofType:@"png"] UTF8String]);
    char *output_image = strdup([[[NSBundle mainBundle] pathForResource:@"iphone" ofType:@"png"] UTF8String]);
    char *argv[] = { "convert", input_image, "-resize", "100x100", output_image, NULL };

    // ConvertImageCommand(ImageInfo *, int, char **, char **, MagickExceptionInfo *);
    status = ConvertImageCommand(imageInfo, 5, argv, NULL, exceptionInfo);

    free(input_image);
    free(output_image);

    if (status == MagickFalse) {
        ThrowWandException(magick_wand); // Always throws an exception here...
    }

    size_t my_size;
    unsigned char * my_image = MagickGetImageBlob(magick_wand, &my_size);
    NSData * data = [[NSData alloc] initWithBytes:my_image length:my_size];
    free(my_image);
    magick_wand = DestroyMagickWand(magick_wand);
    MagickWandTerminus();
    UIImage * image = [[UIImage alloc] initWithData:data];
    [data release];

    [imageViewButton setImage:image forState:UIControlStateNormal];
    [image release];
}

The problem is that status is always MagickFalse, which means it throws an exception. I'm also not sure whether I'm using ConvertImageCommand() in the correct way either.

Any help would be greatly appreciated. Thanks in advance.

Answer 1

I ended up using MagickCommandGenesis() to achieve the desired result.

Answer 2

None of these are the right answer. The code above is just plain wrong and has been copied and pasted all over the internet in some form or another

http://www.imagemagick.org/discourse-server/viewtopic.php?t=19504 http://www.imagemagick.org/discourse-server/viewtopic.php?t=25430 iPhone ImageMagick Library - converting from batch file script to Objective-C using MagickWand API http://www.imagemagick.org/discourse-server/viewtopic.php?f=6&t=20527

the list goes on

MagicWand is the framework to do image manipulations using the imagemagick API, whereas ConvertImageCommand calls directly into the commandline interface for the convert command. If you wish to do things through imagemagick's api, then use MagicWand etc, but if you wish to simply call into the same method that is used from the commandline, then call ConvertImageCommand.

The fact that it is returning MagickFalse is correct. While I don't claim to have read the whole method and know everything it's doing or why, if you look at convert.c http://www.imagemagick.org/api/MagickWand/convert_8c_source.html, the last few lines of the function are

3217   status&=WriteImages(image_info,image,argv[argc-1],exception);
 3218   if (metadata != (char **) NULL)
 3219     {
 3220       char
 3221         *text;
 3222 
 3223       text=InterpretImageProperties(image_info,image,format);
 3224       if (text == (char *) NULL)
 3225         ThrowConvertException(ResourceLimitError,"MemoryAllocationFailed",
 3226           GetExceptionMessage(errno));
 3227       (void) ConcatenateString(&(*metadata),text);
 3228       text=DestroyString(text);
 3229     }
 3230   DestroyConvert();
 3231   return(status != 0 ? MagickTrue : MagickFalse);
 3232 }

What it says is to return 0 (MagickFalse) on success when called from the commandline, which is fairly reasonable.

The above code will work fine without all the MagicWand stuff as so -

// Resize image.
    ImageInfo *imageInfo = AcquireImageInfo();
    ExceptionInfo *exceptionInfo = AcquireExceptionInfo();

    // Get image from bundle.
    char *input_image = strdup([[[NSBundle mainBundle] pathForResource:@"iphone" ofType:@"png"] UTF8String]);
    char *output_image = strdup([[[NSBundle mainBundle] pathForResource:@"iphone" ofType:@"png"] UTF8String]);
    char *argv[] = { "convert", input_image, "-resize", "100x100", output_image, NULL };

    // ConvertImageCommand(ImageInfo *, int, char **, char **, MagickExceptionInfo *);
    status = ConvertImageCommand(imageInfo, 5, argv, NULL, exceptionInfo);

Alternatively, if you want to use the API directly, then there are plenty of samples online that provide examples of how to use MagicWand.

The above code is attempting to mix and match two different methodologies. The MagicWand instantiation above is not doing anything, and if you will look at the image in the NSData at the end of the above code snippet, it is the same image you started with. The output of the ConvertImageCommand ought to be what you're expecting though.