Re: [Openexr-devel] writing an exr

[Florian Kainz]

Kevin Smith wrote:
> 
>    Can anyone share some boilerplater code for writing an exr image? Something
> as simple as writing out a 512x512, middle grey (0.18) .exr would be great.
> 

Hi Kevin,

below are two versions of a function that creates an image
and stores it in an OpenEXR file.  One version first creates
the whole image in a frame buffer and then saves it.  The
other version creates the image one scanline at a time, and
saves each scanline as soon as possible.
The OpenEXR interface allows many other variations: instead
of containing the whole image, or only a single scanline, the
frame buffer might contain a small number of scanlines, its
layout in memory may be non-contiguous, etc.

hope this helps,

Florian



#include <ImfRgbaFile.h>
#include <ImfArray.h>

using namespace Imf;
using namespace std;


void
writeImageFullFrameBuffer (const char fileName[], int width, int height)
{
    // Create a frame buffer, and fill it with some pattern

    Array2D<Rgba> pixels (height, width);

    for (int y = 0; y < height; ++y)
        for (int x = 0; x < width; ++x)
        {
            Rgba &p = pixels[y][x];
            p.r = (y % 5) * 0.2;
            p.g = (x % 5) * 0.2;
            p.b = 0.18;
        }

    // Store the frame buffer's contents in an OpenEXR file

    Header header (width, height);
    RgbaOutputFile out (fileName, header, WRITE_RGB);
    out.setFrameBuffer (&pixels[0][0], 1, width);
    out.writePixels (height);
}


void
writeImageSingleScanLine (const char fileName[], int width, int height)
{
    // Create a frame buffer for a single scanline

    Array<Rgba> pixels (width);

    // Generate an image, one scanline at a time,
    // and store it in the OpenEXR file.

    Header header (width, height);
    RgbaOutputFile out (fileName, header, WRITE_RGB);
    out.setFrameBuffer (&pixels[0], 1, 0);

    for (int y = 0; y < height; ++y)
    {
        for (int x = 0; x < width; ++x)
        {
            Rgba &p = pixels[x];
            p.r = (y % 5) * 0.2;
            p.g = (x % 5) * 0.2;
            p.b = 0.18;
        }

        out.writePixels (1);
    }
}


int
main ()
{
    try
    {
        writeImageFullFrameBuffer ("test1.exr", 512, 512);
        writeImageSingleScanLine  ("test2.exr", 512, 512);
    }
    catch (const std::exception &e)
    {
        cerr << e.what() << endl;
    }

    return 0;
}