[Interest] QImage::Format_Grayscale8 work working

[Jason H]

5.10.1

Yes, that's a good idea. So I wrote some code:

	QImage gray8 = color8(image, Qt::gray, QImage::Format_Grayscale8); // modded my function to take the format.
	QImage index = color8(image, Qt::gray, QImage::Format_Indexed8);

	int differences = 0;
	int same = 0;
	for (int y=0; y < gray8.height(); y++) {
		for (int x=0; x < gray8.width(); x++) {
			qDebug() << "gray" << gray8.pixel(x,y) << "index" << index.pixel(x,y);
			if (gray8.pixel(x,y) != index.pixel(x,y) )
				differences++;
			else
				same++;
		}
	}

	qDebug() << "differences" <<  differences;
	qDebug() << "same" <<  same;

With output:
differences 8048393
same 72951

It seems every pixel from "gray8" is 4278190080 == 0xFF000000.
So it seems that setPixel in my color8 function never sets the pixel.

I'm thinking this is a bug, unless someone has an idea?


> Sent: Friday, March 16, 2018 at 9:52 AM
> From: "Nikolai Tasev" <nikolai at nand.bg>
> To: "Jason H" <jhihn at gmx.com>
> Cc: "Interestqt-project.org" <Interest at qt-project.org>
> Subject: Re: [Interest] QImage::Format_Grayscale8 work working
>
> I am not sure if there any difference in how the Indexed8 and Grayscale8 
> are saved. It also depends on the
> file format. As far as I remember many formats always save as 32bits.
> 
> First look at the pixel data as raw unsigned char values to see if the 
> conversion is correct, maybe the problem comes
> later when saving. Then you can also try with some small synthetic 
> images for specialized tests.
> 
> Grayscale8 is a most recent development is there any chance that you use 
> a newer header and older library?
> 
> On 3/16/2018 3:14 PM, Jason H wrote:
> > It returns black. All black. Hence the issue :-)
> > The original file is an 8MP 4:3 image as png it saves to ~10mb.
> > - as a Grayscale8 it saves as 8 KB-kilo. (should be 8,121,344)
> > - as Indexed8 it saves as 5.5mb
> >
> > I'd expect Greyscale8 to be about the same size on disk as Indexed8 +/- color table.
> >
> >> Sent: Friday, March 16, 2018 at 8:38 AM
> >> From: "Nikolai Tasev" <nikolai at nand.bg>
> >> To: "Jason H" <jhihn at gmx.com>
> >> Cc: "Interestqt-project.org" <Interest at qt-project.org>
> >> Subject: Re: [Interest] QImage::Format_Grayscale8 work working
> >>
> >> 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
> >>>>>
> >>
> 
>