ImageMagick to write image file row by row (or band by band)

Question

Does ImageMagick (C API MagickWand) have a functionality to generate an image file (.jpg, .tif) using RGB raster data?

If so, can it also generate an image file band by band, meaning write few rows at a time until it writes the whole image? Or one row at a time?

You do not write "one row at a time" to a .jpg file. I suggest you explore the documentation for ImageMagick. — Weather Vane, Mar 24 '17 at 20:32
BTW the `imagemagick` tag says it *"is an open source software suite for displaying, converting and editing raster image files."* — Weather Vane, Mar 24 '17 at 20:45
Yes, you need `MagickWandGenesis()`, `NewMagickWand()`,`MagickNewImage()`, then `MagickImportImagePixels()` to read your arbitrary RGB pixels. — Mark Setchell, Mar 25 '17 at 16:26

score 2 · Accepted Answer · answered Mar 27 '17 at 16:21

I believe you are describing image row iterators. ImageMagick provided PixelIterator methods to allow traversing of image data.

Here's a quick example.

#include <stdio.h>
#include <wand/MagickWand.h>

int main(int argc, const char * argv[]) {
    // Set up IM environment.
    MagickWandGenesis();

    // Prototype
    MagickWand * wand;
    PixelWand * bg;
    PixelIterator * iter;
    PixelWand ** row;
    MagickPixelPacket pixel;

    size_t
        x,
        y,
        row_width,
        width  = 200,
        height = 50;

    unsigned int
        seed = 0xABCD;

    // Allocate & initialize.
    wand = NewMagickWand();
    bg = NewPixelWand();

    // Create an empty image.
    PixelSetColor(bg, "WHITE");
    MagickNewImage(wand, width, height, bg);

    // Free color resource.
    bg = DestroyPixelWand(bg);

    srand(seed); // Seed random number.

    // Allocate & initialize pixel iterator
    iter = NewPixelIterator(wand);

    // Loop through all rows.
    for (y = 0; y < height; ++ y)
    {
        // Pull all pixels in a row.
        row = PixelGetNextIteratorRow(iter, &row_width);
        // Iterate over all pixels collected.
        for (x = 0; x < row_width; ++x)
        {
            // Copy pixel data to packet.
            PixelGetMagickColor(row[x], &pixel);
            // Set random colors.
            pixel.red   = rand() & QuantumRange;
            pixel.green = rand() & QuantumRange;
            pixel.blue  = rand() & QuantumRange;
            // Put data back to pixel from packet.
            PixelSetMagickColor(row[x], &pixel);
        }
        // Sync manipulated data on buffer back to image.
        PixelSyncIterator(iter);
    }

    /******************************
     Let's set row 16 to be all RED
     ******************************/
    PixelSetIteratorRow(iter, 15);
    row = PixelGetNextIteratorRow(iter, &row_width);
    for (x = 0; x < row_width; ++x)
    {
        PixelGetMagickColor(row[x], &pixel);
        pixel.red   = QuantumRange;
        pixel.green = 0;
        pixel.blue  = 0;
        PixelSetMagickColor(row[x], &pixel);
    }
    // Sync manipulated data on buffer back to image.
    PixelSyncIterator(iter);

    // Free iterator resorce.
    iter = DestroyPixelIterator(iter);

    MagickWriteImage(wand, "/tmp/output.png");
    // Free image data.
    wand = DestroyMagickWand(wand);

    MagickWandTerminus();
    return 0;
}

Please note that the above example uses ImageMagick 6. For ImageMagick 7, please review Porting Guide.

for ImageMagick 7. use PixelInfo pixel instead of MagickPixelPacket pixel, and PixelSetPixelColor instead of PixelSetMagickColor. Refer [this](http://www.imagemagick.org/api/MagickCore/pixel_8h_source.html) — Rahul, May 18 '17 at 10:11

ImageMagick to write image file row by row (or band by band)

1 Answers1