declaring unknown number of image array problem

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hi,
I've written a code to save desktop images into unknown number of image array. but when I run the code below it shows this problem : "Object reference not set to an instance of an object.". I know that says that I need to declare image like this : image[] i=new image[100], but I don't know my images are 100 or more or less. please help me about it.
code :

private int num;
private Image[] i;
private void timer1_Tick(object sender, EventArgs e)
{
SendKeys.Send("{PRTSC}");
i[num] = Clipboard.GetImage();
num++;
}

Thanks.

Posted 3-Feb-12 9:12am

mehdi_k

Updated 3-Feb-12 23:57pm

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Wendelius · Accepted Answer · 2012-02-03T09:15:00

Solution 1

Instead of an array, consider using as generic list: List<t> Class[^]. Now with Add[^] method you can add the necessary items and the list expands automatically.

Posted 3-Feb-12 9:15am

Wendelius

Comments

mehdi_k 3-Feb-12 15:40pm

Thanks , it work great.
but when I run it, it uses lots of cpu(about 50%), and my RAM(memory) gets full after 1 or 2 min. is there a way to fix this? I mean this app gets useless with this situation.

Wendelius 3-Feb-12 15:55pm

Without any more information, I'd guess that the images are filling up the memory. what type did you use for the generics declaration?

mehdi_k 3-Feb-12 16:07pm

I used image as I am trying to copy images from clipboard. like this : private List<Image> i = new List<Image>();

Wendelius 3-Feb-12 16:20pm

Could it simply be that the total amount of the image data is so high that it's causing thse problems. For example if each image is 5 MB and you have 100 of them that's total 500 MB plus the overhead of the list (which shouldn't be too high).

Just out of curiosity you could also try using a datatable to store the images. See:DataTable Class[^]. The internals of storing the data are a bit different so it could be performing better (again if the total amount is the problem)

LanFanNinja 3-Feb-12 16:25pm

I agree that this is most likely the problem.

LanFanNinja 3-Feb-12 16:22pm

" is there a way to fix this? "
Install more RAM and possibly a new CPU. =D

Look your source code over there is possibly something in your code you could do different/better. There is really no way we can help you with this problem without more code/information.

To me it seriously just sounds like you are working the crap out of your PC!!

What are you planing on doing with this list of images??

You must find a way to accomplish your task without loading all the images at one time. For example load 20 images do what ever with them then load 20 more ...

mehdi_k 3-Feb-12 16:32pm

I'm just trying to gather these images to make an .avi like an app that records a video from desktop. It's a school training, but important to me to make it work perfectly.

Wendelius 3-Feb-12 16:35pm

Agree that it should work perfectly, it'll show in your grade :) Try using the datatable and if that doesn't help and the amount of images is high, then you propably will have to serialize the data during the process to make the program perform smoothly.

mehdi_k 3-Feb-12 16:52pm

with this, my grade goes below 0 :)

Wendelius 3-Feb-12 17:04pm

No it won't. You'll do just fine :)

LanFanNinja 3-Feb-12 16:45pm

Maybe this would work for you.
Once so many images have been captured (say 50 to 100) write the images in your list out to the hard drive clear the list and repeat.

Or forget the list all together and write them directly to the hard drive as you are capturing.

Then once you are through capturing you can load the images back into the app (only so many at a time though) to do whatever else you may need to do with them.

mehdi_k 3-Feb-12 16:52pm

I've tried to save them directly to the hard. memory is ok but cpu goes over 70-80%.

LanFanNinja 3-Feb-12 17:01pm

To fix your CPU performance problem try capturing at 60 frames per second. 60 frames per second is about the maximum framerate our eyes can process, anything above tends to be imperceptible to us.

Set your timer tick interval to 16.67 milliseconds and see how that works for you.

Wendelius 3-Feb-12 17:05pm

That should help. I'd even lower the frame rate to 25...

LanFanNinja 3-Feb-12 17:06pm

Yes 25fps should still be pretty smooth.

EDIT: Just in case OP is not familiar with how to calculate this just divide 1000 by the desired frame rate and this will give you milliseconds interval at which you need to capture the images.

Example:
1000 / 25 = 40ms

mehdi_k 4-Feb-12 5:21am

I even set timer interval to 100, still over 80-90% cpu usage with this code :

private int num;
private void timer1_Tick(object sender, EventArgs e)
{
SendKeys.Send("{PRTSC}");
Image i = Clipboard.GetImage();
i.Save("pics\\" + num, System.Drawing.Imaging.ImageFormat.Png);
num++;
}

LanFanNinja 4-Feb-12 5:40am

Let me play around with this code you posted and see if I can figure something out.

Can you tell me the specs. of your CPU?

mehdi_k 4-Feb-12 5:55am

intel dual core 2200

LanFanNinja 4-Feb-12 7:12am

I am sorry I am not able to optimize this code (at least not using managed code). I have never created a screen recorder app and I am realizing This is just a very CPU intensive task to do! Even searching google was of no help as it seems others who have set out to accomplish this task have run into the same problems with no answers to be found. :(

Perhaps you could post this as a new question and see if someone else knows how to optimize it.

Either way I think your instructor will be happy with your code.

Once again I am sorry I could not be more helpful and I wish you the best of luck.

mehdi_k 4-Feb-12 15:30pm

Thanks for trying

LanFanNinja 4-Feb-12 15:52pm

You're welcome.

Wendelius 4-Feb-12 7:31am

If you're now saving the image to a file, release the resources with dispose:

private int num;
private void timer1_Tick(object sender, EventArgs e)
{
SendKeys.Send("{PRTSC}");
Image i = Clipboard.GetImage();
i.Save("pics\\" + num, System.Drawing.Imaging.ImageFormat.Png);
i.Dispose();
num++;
}

mehdi_k 4-Feb-12 15:33pm

it's good but nothing about CPU usage. maybe I need to make a post to find out how to optimize the code.
Thanks

LanFanNinja 3-Feb-12 17:19pm

See my comment to Mika Wendelius for info on how to calculate frame rate if you do not know this already.

LanFanNinja 3-Feb-12 16:30pm

+5

Wendelius 3-Feb-12 16:32pm

Thanks :)