Yes that confirms my suspicions that setPixel for Format_Grayscale8
expect different things ( as I wrote in my previous email).
You need to pass qRgb(qRed(rgbVal), 0, 0) for red, not qRed(rgbVal).
On 3/16/2018 4:09 PM, Jason H wrote:
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" <niko...@nand.bg>
To: "Jason H" <jh...@gmx.com>
Cc: "Interestqt-project.org" <Interest@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" <niko...@nand.bg>
To: "Jason H" <jh...@gmx.com>
Cc: "Interestqt-project.org" <Interest@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" <niko...@nand.bg>
To: "Jason H" <jh...@gmx.com>, "Interestqt-project.org"
<Interest@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?
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