QT QImage Read From Error
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@Christian-Ehrlicher
This is the codewhile(true) { bool check = doesFilexExist(image_path); if(check){ QImage image; bool result = image.load(image_path); QThread::msleep(20); if(!image.isNull()){ qDebug() << "==> Timestamp for image grabbing: " << QTime::currentTime(); emit sendImage(image); QFile::remove(image_path); QThread::msleep(50); } } else { // Do nothing } }@Christian-Ehrlicher said in QT QImage Read From Error:
So you say the image reading take too long?
I'm not so sure about that.
The logic is very simple :
1. Check if image exists in folder.
2.if exists, load image
3.emit the image
4. delete image from the folderNote: 3rd party camera stores a single image in that folder
@mvsri Have you thought about using QFileSystemWatcher to listen to changes in the folder,?
No need to reinvent the wheel, you can simply react to the
directoryChangedsignal
If @Christian-Ehrlicher is right, and the camera overwrites the image, than the fileChanged signal will be much handier to use.
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@mvsri So are you sure the camera does not override the image while you try to load it? Please try without the camera with a static image.
wrote on 9 Sept 2020, 09:42 last edited by@Christian-Ehrlicher
I think the camera does override the image when i try to load it because when i tested it with static image the code worked perfectly -
@mvsri Have you thought about using QFileSystemWatcher to listen to changes in the folder,?
No need to reinvent the wheel, you can simply react to the
directoryChangedsignal
If @Christian-Ehrlicher is right, and the camera overwrites the image, than the fileChanged signal will be much handier to use.
wrote on 9 Sept 2020, 09:43 last edited by@J-Hilk said in QT QImage Read From Error:
@mvsri Have you thought about using QFileSystemWatcher to listen to changes in the folder,?
I haven't thought about that will try to use it now.
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@Christian-Ehrlicher
I think the camera does override the image when i try to load it because when i tested it with static image the code worked perfectly@mvsri said in QT QImage Read From Error:
I think the camera does override the image when i try to load it because when i tested it with static image the code worked perfectly
So you've your explanation of the issue - Qt can't do anything against this.
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@mvsri said in QT QImage Read From Error:
I think the camera does override the image when i try to load it because when i tested it with static image the code worked perfectly
So you've your explanation of the issue - Qt can't do anything against this.
wrote on 9 Sept 2020, 09:47 last edited by@Christian-Ehrlicher
yeah i got that, but the thing is if you see the code,
after reading the image i'm deleting the image from the folder, so the chances for image override is very less -
@Christian-Ehrlicher
yeah i got that, but the thing is if you see the code,
after reading the image i'm deleting the image from the folder, so the chances for image override is very less@mvsri Maybe try to rename it before you try to read it.
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wrote on 9 Sept 2020, 10:01 last edited by
Maybe try to find out if that 3rd party camera has other API than save the image to the disk.
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@Christian-Ehrlicher
yeah i got that, but the thing is if you see the code,
after reading the image i'm deleting the image from the folder, so the chances for image override is very lesswrote on 9 Sept 2020, 10:01 last edited by@mvsri
I really don't understand what is going on! What is it that produces thatimage_pathfile? Something external? How do you know that whatever is creating it has finished writing the file and flushed it before your thread decides to read it in, such that it might read in something incomplete? :confused: -
@mvsri
I really don't understand what is going on! What is it that produces thatimage_pathfile? Something external? How do you know that whatever is creating it has finished writing the file and flushed it before your thread decides to read it in, such that it might read in something incomplete? :confused:wrote on 9 Sept 2020, 10:17 last edited by@JonB said in QT QImage Read From Error:
@mvsri
I really don't understand what is going on! What is it that produces thatimage_pathfile? Something external? How do you know that whatever is creating it has finished writing the file and flushed it before your thread decides to read it in, such that it might read in something incomplete? :confused:image_path is nothing but a QString which stores the path to a bmp image in a folder. the path is static it doesn't change.
I don't know whether the image writing is finished or not. that's why i used QFile exists to check if the file is created or not and read the image if the path exists.
I also have the same doubt whether i'm reading the image in an incomplete mode.@Christian-Ehrlicher said in QT QImage Read From Error:
@mvsri Maybe try to rename it before you try to read it.
I'm trying it now.
Thank you everyone for all the help. will try to update if i found something useful.
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@JonB said in QT QImage Read From Error:
@mvsri
I really don't understand what is going on! What is it that produces thatimage_pathfile? Something external? How do you know that whatever is creating it has finished writing the file and flushed it before your thread decides to read it in, such that it might read in something incomplete? :confused:image_path is nothing but a QString which stores the path to a bmp image in a folder. the path is static it doesn't change.
I don't know whether the image writing is finished or not. that's why i used QFile exists to check if the file is created or not and read the image if the path exists.
I also have the same doubt whether i'm reading the image in an incomplete mode.@Christian-Ehrlicher said in QT QImage Read From Error:
@mvsri Maybe try to rename it before you try to read it.
I'm trying it now.
Thank you everyone for all the help. will try to update if i found something useful.
wrote on 9 Sept 2020, 10:23 last edited by JonB 9 Sept 2020, 10:32@mvsri said in QT QImage Read From Error:
image_path is nothing but a QString which stores the path to a bmp image in a folder. the path is static it doesn't change.
I know that! My question is about the content of that file.
I don't know whether the image writing is finished or not. that's why i used QFile exists to check if the file is created or not and read the image if the path exists.
But that doesn't tell you anything about whether it has started but not finished writing to that file, does it? (Unless you are relying on Windows or something not allowing a file to satisfy "exists" until it has been closed, which I would see as dodgy in the extreme.) In which case, you will read in an incomplete image file, maybe that's why you have "black" at the bottom? At least put in a
qDebug() << image.sizeInBytes()after loading it (though I'm not sure if that's reliable)....QFile::remove(image_path);It gets worse! This, or renaming: how do you know that at the instant you execute this the camera has not re-started writing to that file for the next capture, and you are (trying to) removing/renaming a file while it is being written anew?
Is your camera-image-capture-write-to-file a separate process from your code? How do you know when the capture has started/finished writing to the file?
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