Create Leptonica PIX struct from UIImage

Question

I want to create a PIX data structure from a UIImage. The struct of PIX:

struct Pix
{
     l_uint32             w;           /* width in pixels                   */
     l_uint32             h;           /* height in pixels                  */
     l_uint32             d;           /* depth in bits                     */
     l_uint32             wpl;         /* 32-bit words/line                 */
     l_uint32             refcount;    /* reference count (1 if no clones)  */
     l_int32              xres;        /* image res (ppi) in x direction    */
                                       /* (use 0 if unknown)                */
     l_int32              yres;        /* image res (ppi) in y direction    */
                                       /* (use 0 if unknown)                */
     l_int32              informat;    /* input file format, IFF_*          */
     char                *text;        /* text string associated with pix   */
     struct PixColormap  *colormap;    /* colormap (may be null)            */
     l_uint32            *data;        /* the image data                    */
 };
 typedef struct Pix PIX;


struct PixColormap
 {
     void            *array;     /* colormap table (array of RGBA_QUAD)     */
     l_int32          depth;     /* of pix (1, 2, 4 or 8 bpp)               */
     l_int32          nalloc;    /* number of color entries allocated       */
     l_int32          n;         /* number of color entries used            */
};

How can I do this in iOS?

score 0 · Answer 1 · answered Aug 03 '12 at 17:20

0

You will start with a UIImage, then get a CGImageRef from that using "CGImage". With a CGImageRef you can query it for the width, height, depth, wpl (which will you will get as bytesPerRow from the image, then modify by dividing by the pixel size). To get the data you need to render it into a context, get the point, then copy that data into a NSData object. The size will be the number of rows by the bytesPerRow value.

answered Aug 03 '12 at 17:20

David H

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Hey David, I was wondering if you could do me a huge favour and help me out here? I have been struggling for a couple of days to get it working. It seems you know what you are doing and I would really appreciate it. Thank you so much, really means a lot. stackoverflow.com/questions/17096618/leptonica-apply-threshold – Teddy13 Jun 15 '13 at 01:14

score 0 · Accepted Answer · answered Aug 03 '12 at 17:26

You can create a CGBitmapContext and draw the image into it. You need to use the RGB color space to create the context. You may need to experiment with kCGBitmapByteOrder32Little and kCGBitmapByteOrder32Big in the bitmapInfo argument to get the R, G, and B components in the correct order.

Then you can initialize your struct Pix from that, using functions like CGBitmapContextGetWidth, CGBitmapContextGetBytesPerRow, and CGBitmapContextGetData. The xres, yres, informat, text, and colormap elements don't correspond to any attributes of CGBitmapContext or UIImage, so you should probably set them to 0 or NULL.

Take a look at the CGBitmapContext Reference for help with CGBitmapContext.

Also look at the Quartz 2D Programming Guide for help creating a bitmap context, and for help drawing your image into the context.

Unfortunately (for you), I don't know anything about Leptonica. I was able to answer this question based on my knowledge of Core Graphics, the C programming language, and the `struct` definitions in the question. — rob mayoff, Jun 15 '13 at 00:53

Create Leptonica PIX struct from UIImage

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