Image Formats NG

Image Formats NG project is the Next Generation of the Qt Image Formats.

Problematic

There are some problems with current image formats:

• It is not possible to read a image that contains multiple frames and mipmaps, only one-dimention arrays are supported.
• It is not possible to write an animation or a mipmapped image.
• It is not possible to check what options are supported in case when image can contain different subtypes (for example, dds can contain jpeg inside, which supports different compression levels, or plain data without compression)
• Extending image formats framework is hard because of huge usage of virtual functions (it is not possible to add new virtual functions without breaking BC)

Basic reading

Basically, you used QImageReader to read an image from the file.

#include <QImageReader>
#include <QDebug>

void handleImage(const QImage &image);

int main(int argc, char *argv[])
{
    QImageReader reader("image.png");
    QImage image = reader.read();
    if (image.isNull()) {
        qWarning() << "Error reading image" << reader.errorString();
        return 1;
    }

    handleImage(image);
    return 0;
}

Now, you should use an ImageIO class instead.

#include <ImageIO>
#include <QDebug>

void handleImage(const QImage &image);

int main(int argc, char *argv[])
{
    ImageIO reader("image.png");
    auto result = reader.read();
    ImageIOResult ok = result.first;
    if (!ok) {
        qWarning() << "Error reading image:" << ok.toString();
        return 1;
    }
    ImageContents contents = result.second;
    handleImage(contents.image());
    return 0;
}

Basic writing

Simple writing is done almost the same way as with QImageWriter.

#include <ImageIO>
#include <QDebug>

QImage createImage();

int main(int argc, char *argv[])
{
    QImage image = createImage();
    ImageIO writer("image.png");
    ImageContents contents(image);
    ImageIOResult ok = writer.write(contents);
    if (!ok) {
        qWarning() << "Error writing image:" << ok.toString();
        return 1;
    }
    return 0;
}

Reading image meta data

It is possible to read image meta data without reading the whole contents of the file.

#include <ImageIO>
#include <QDebug>

int main(int argc, char *argv[])
{
    ImageIO reader("image.png");
    const auto result = reader.readHeader();
    if (!result.first) {
        qWarning() << "Error reading header:" << result.first.toString();
        return 1;
    }
    ImageHeader header = result.second;
    qDebug() << "size = " << header.size();
    qDebug() << "format = " << header.imageFormat();
    qDebug() << "image count = " << header.imageCount();
    qDebug() << "mipmap count = " << header.mipmapCount();

    const auto contentsResult = reader.readContents(header);
    // if (!contentsResult.first) ...

    return 0;
}

Complex reading

Image Formats NG supports rather complex data structures. First, there can be one of three types of images - a simple 1d/2d image, represented by a QImage, a 6-sided cubemap, represented by CubeTexture and a 3d texture, represented by VolumeTexture. Second, there can be multiple 'frames' (for example, GIF file is an array of images). Third, each frame can have prescaled images of different sizes, i.e. mipmaps (for example, icns is a single image with mipmaps).

The most complex file can be read as follows.

#include <ImageIO>
#include <QDebug>

int main(int argc, char *argv[])
{
    ImageIO reader("texture.dds");
    const auto result = reader.read();

    // if (!result.first) ...

    const auto &contents = result.second;
    for (int index = 0; index < contents.header().imageCount(); ++index) { // read array
        for (int level = 0; level < contents.header().mipmapCount(); ++level) { // read mipmaps
            ImageResource resource = contents.resource(index, level);
            if (resource.type() == ImageResource::Type::Image) {
                const QImage image = resource.image();
                // ...
            } else if (resource.type() == ImageResource::Type::CubeTexture) {
                CubeTexture texture = resource.cubeTexture();
                // ...
            } else if (resource.type() == ImageResource::Type::VolumeTexture) {
                VolumeTexture texture = resource.volumeTexture();
                // ...
            }
        }
    }

    ImageExifMeta exif = contents.exifMeta();
    if (!exif.isEmpty()) {
        // ...
    }

    return 0;
}