Re: [Openexr-devel] Writing OpenEXR file, one scanline at a time

[Piotr Stanczyk]

Hi Nicholas,

 

I suspect you'd be better off using the generic interface. There is an example in the docs that speaks to the computation of the offsets required to achieve just such a thing.

-Piotr

On 23 June 2015 at 16:21, Nicholas Yue <address@hidden> wrote:

Hi,

  I have having difficult working out the correct stride logic to write one scanline at a time to an OpenEXR file.

  The example code shows write the entire array in memory but I only have access to a single scanline at a time.

  I want to minimize the memory usage by not storing the entire image before writing.

  Here is the code.

  Thanks in advance.

#include <stdio.h>

#include <string>

#include <OpenEXR/ImfOutputFile.h>

#include <OpenEXR/ImfArray.h>

#include <OpenEXR/ImfCompression.h>

#include <OpenEXR/ImfChannelList.h>

#include <OpenEXR/ImfRgba.h>

// This is currently NOT working but would be a useful example to have

void writeIncrementalScanline (const std::string& fileName,

  int width,

  int height)

{

float pixelAspectRatio = 1;

const Imath::V2f screenWindowCenter = Imath::V2f (0, 0);

float screenWindowWidth = 1;

Imf::LineOrder lineOrder = Imf::INCREASING_Y;

Imf::Compression compression = Imf::ZIPS_COMPRESSION;

Imf::Header header(width, height,

  pixelAspectRatio,

  screenWindowCenter,

  screenWindowWidth,

  lineOrder,

  compression);

header.channels().insert("rgba.R",Imf::Channel(Imf::HALF));

header.channels().insert("rgba.G",Imf::Channel(Imf::HALF));

header.channels().insert("rgba.B",Imf::Channel(Imf::HALF));

header.channels().insert("rgba.A",Imf::Channel(Imf::HALF));

Imf::OutputFile file (fileName.c_str(), header);

Imf::FrameBuffer framebuffer;

Imf::Array2D<half> redBuffer(width,1);

Imf::Array2D<half> greenBuffer(width,1);

Imf::Array2D<half> blueBuffer(width,1);

Imf::Array2D<half> alphaBuffer(width,1);

half colorChannelGreyScaleDelta = 1.0f/float(height-1);

std::cout << "colorChannelGreyScaleDelta = " << colorChannelGreyScaleDelta << std::endl;

std::cout << "height * colorChannelGreyScaleDelta = " << height * colorChannelGreyScaleDelta << std::endl;

size_t xStride = sizeof(half) * 1;

size_t yStride = width;

const half *redPixels   = &redBuffer[0][0];

const half *greenPixels = &greenBuffer[0][0];

const half *bluePixels  = &blueBuffer[0][0];

const half *alphaPixels = &alphaBuffer[0][0];

framebuffer.insert("rgba.R",

  Imf::Slice(Imf::HALF,

 (char *)redPixels,

 xStride,

 yStride));

framebuffer.insert("rgba.G",

  Imf::Slice(Imf::HALF,

 (char *)greenPixels,

 xStride,

 yStride));

framebuffer.insert("rgba.B",

  Imf::Slice(Imf::HALF,

 (char *)bluePixels,

 xStride,

 yStride));

framebuffer.insert("rgba.A",

  Imf::Slice(Imf::HALF,

 (char *)alphaPixels,

 xStride,

 yStride));

for (int h=0;h<height;h++)

{

half grey_scale_value = colorChannelGreyScaleDelta * h;

for (int w=0;w<width;w++)

{

redBuffer[w][0]   = 1.;//grey_scale_value;

greenBuffer[w][0] = 1.;//grey_scale_value;

blueBuffer[w][0]  = 1.;//grey_scale_value;

alphaBuffer[w][0] = 1.;

}

file.setFrameBuffer(framebuffer);

file.writePixels();

}

}

int main()

{

    const std::string fileName("IncrementalScanline.exr");

    const int width = 256;

    const int height = 512;

    writeIncrementalScanline (fileName, width, height);

    return 0;

}

Cheers
--

Nicholas Yue

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