[Interest] QImage::Format_Grayscale8 work working

Nikolai Tasev nikolai at nand.bg
Fri Mar 16 13:38:45 CET 2018

What is not working for Grayscale? Looking at the code it will do 
different things when you are passing Qt::red, Qt::blue, Qt::green.
It will not return a color image but a grayscale image of the 
corresponding channel.

On 3/16/2018 2:08 PM, Jason H wrote:
>> Sent: Friday, March 16, 2018 at 9:12 AM
>> From: "Nikolai Tasev" <nikolai at nand.bg>
>> To: "Jason H" <jhihn at gmx.com>, "Interestqt-project.org" <Interest at qt-project.org>
>> Subject: Re: [Interest] QImage::Format_Grayscale8 work working
>> Format_Indexed8 and Format_Grayscale8 both have 8bit per pixel. The
>> difference is that to convert from the 8bit pixel to RGB values
>> (QImage::pixel() method)
>> for Indexed8u you need to set the Palette for conversion and for
>> Grayscale8 you don't (it just assumes that R=G=B=gray value)
> I am aware of that.
>> Are you trying to extract a channel from a multichannel image and put it
>> into a grayscale image? The code seems unnecessary complex
>> and inefficient for such a task. You just need to get the data pointer
>> and skip the uneeded channels and keep watch for the end of the row.
> That assumes I be want to do the math for every Format. ARGB is easy, RGB888 is not, etc. Pixel() alerts need to not care. Yes, I could use scan lines, but then each format requires code. Which I haven't got time to write now.
> Anyway, I be still believe my code is correct, and it's still not working.
>> On 3/15/2018 10:21 PM, Jason H wrote:
>>> Given the following functions, I should be able to create a non-all black image (assuming input is good)? The only success I have is using Indexed8
>>> QHash<QRgb, qint32 (*)(QRgb)> colorFuncs {
>>> 	{ Qt::red,   qRed},
>>> 	{ Qt::green, qGreen},
>>> 	{ Qt::blue,  qBlue},
>>> 	{ Qt::gray,  qGray},
>>> };
>>> QImage color8(const QImage &image, int channel) { // Channel is one of Qt::red Qt::green Qt::blue or Qt::gray
>>> 	QImage out(image.width(), image.height(), QImage::Format_Indexed8);  // Change to Format_Grayscale8, and get nothing
>>> // for indexed8
>>> 	QVector<QRgb> values;
>>> 	values.reserve(256);
>>> 	if (channel==Qt::gray) { for (int c=0; c<256; c++) values.append(qRgb(c,c,c)); }
>>> 	if (channel==Qt::red)  { for (int c=0; c<256; c++) values.append(qRgb(c,0,0)); }
>>> 	if (channel==Qt::green){ for (int c=0; c<256; c++) values.append(qRgb(0,c,0)); }
>>> 	if (channel==Qt::blue) { for (int c=0; c<256; c++) values.append(qRgb(0,0,c)); }
>>> 	out.setColorTable(values);
>>> // end for indexed8
>>> 	int (*colorFunc)(QRgb rgb) = colorFuncs[channel];
>>> 	for (int y=0; y < image.height(); y++) {
>>> 		for (int x=0; x < image.width(); x++) {
>>> 			out.setPixel(x,y, colorFunc(image.pixel(x,y)));
>>> 		}
>>> 	}
>>> 	return out;
>>> }
>>> I'm not familar with Qt and Grayscale8... Anyone know what is going wrong?
>>> _______________________________________________
>>> Interest mailing list
>>> Interest at qt-project.org
>>> http://lists.qt-project.org/mailman/listinfo/interest

More information about the Interest mailing list