如何从浮点数组创建一个新的QImage [英] how to create a new QImage from an array of floats

问题描述

我有一个表示Image的浮点数组。（第一列）。
我想在QGraphicsSecene上将图像显示为QPixmap。为了做到这一点，我尝试使用QImage构造函数从我的数组创建一个新图像 - QImage（const uchar * data，int width，int height，Format format）。
我首先创建了一个新的unsigned char并将我原始数组中的每个值转换为新的unsigned char one，然后尝试使用以下代码创建一个新图像：

I have an array of floats that represents an Image.(column first). I want to show the image on a QGraphicsSecene as a QPixmap. In order to do that I tried to create anew image from my array with the QImage constructor - QImage ( const uchar * data, int width, int height, Format format ). I first created a new unsigned char and casted every value from my original array to new unsigned char one, and then tried to create a new image with the following code:

unsigned char * data = new unsigned char[fres.length()];
for (int i =0; i < fres.length();i++)
    data[i] = char(fres.dataPtr()[i]);

bcg = new QImage(data,fres.cols(),fres.rows(),1,QImage::Format_Mono);

问题在于我尝试以下列方式访问信息：

The problem is when I try to access the information in the following way:

bcg-> pixel（i，j）;

bcg->pixel(i,j);

我只得到值12345.
如何创建一个我的数组中的可见图像。
谢谢

I get only the value 12345. How can I create a viewable image from my array. Thanks

推荐答案

这里有两个问题。

一，将 float 转换为 char 只需将 float ，因此0.3可以舍入为0，0.9可以舍入为 1 。对于0..1的范围， char 将仅包含0或1.

One, casting a float to a char simply rounds the float, so 0.3 may be rounded to 0 and 0.9 may be rounded to 1. For a range of 0..1, the char will only contain 0 or 1.

为char提供全范围，使用乘法：

To give the char the full range, use a multiply:

data[i] = (unsigned char)(fres.dataPtr()[i] * 255);

（另外，您的演员表不正确。）

(Also, your cast was incorrect.)

另一个问题是你的 QImage :: Format 是不正确的; Format_Mono 期望1BPP bitpacked 数据，而不是您期望的8BPP。有两种方法可以解决此问题：

The other problem is that your QImage::Format is incorrect; Format_Mono expects 1BPP bitpacked data, not 8BPP as you're expecting. There are two ways to fix this issue:

// Build a colour table of grayscale
QByteArray data(fres.length());

for (int i = 0; i < fres.length(); ++i) {
    data[i] = (unsigned char)(fres.dataPtr()[i] * 255);
}

QVector<QRgb> grayscale;

for (int i = 0; i < 256; ++i) {
    grayscale.append(qRgb(i, i, i));
}

QImage image(data.constData(), fres.cols(), fres.rows(), QImage::Format_Index8);
image.setColorTable(grayscale);

// Use RGBA directly
QByteArray data(fres.length() * 4);

for (int i = 0, j = 0; i < fres.length(); ++i, j += 4) {
    data[j] = data[j + 1] = data[j + 2] =         // R, G, B
        (unsigned char)(fres.dataPtr()[i] * 255);

    data[j + 4] = ~0;       // Alpha
}

QImage image(data.constData(), fres.cols(), fres.rows(), QImage::Format_ARGB32_Premultiplied);

这篇关于如何从浮点数组创建一个新的QImage的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！