"Undefined variable" error even though variable is defined

2024 2 22
2 个回答
回答已采纳
更新时间：2024 2 23
4 次查看（30 天）

0 个投票

I'm using part of a code I borrowed from @imageanalyst where I'm trying to run through frames of a video to look at how the intensity changes over time. I'd like to perform a background subtraction with the code below
if frame1 == 1
Background1 = thisFrame1;
else
for t=1:frame1
% Change background slightly at each frame
Background1 = (1-alpha1)* thisFrame1 + alpha1 * Background1;
end
end
I get an error stating:
"Unrecognized function or variable 'Background1'.
Background1 = (1-alpha1)* thisFrame1 + alpha1 * Background1;"
even though I have the function defined. when I run the same line of code with a different file, it works fine, even though they're the same file type. any idea as to why this is happening? thanks!

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Stephen23
Stephen23 2024-2-22
编辑：Stephen23 2024-2-22
""Undefined variable" error even though variable is defined"
But is it really defined? On the first loop iteration, what value does Background1 have?

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Steven Lord
Steven Lord 2024-2-23

0 个投票

I'm guessing that you want to initialize Background1 when t is equal to 1 and to use the formula to update Background1 when t is greater than 1. In that case:
for t=1:frame1
if t == 1
Background1 = thisFrame1;
else
% Change background slightly at each frame
Background1 = (1-alpha1)* thisFrame1 + alpha1 * Background1;
end
end
Except that when t is 2, Background1 will be (1-alpha1)*thisFrame1 + alpha1*thisFrame1 = thisFrame1 (assuming there's no code later in the for loop after the if / else block that changes Background1. So perhaps if you describe in more detail what you want to do we can suggest some modifications to your code to achieve your goal.

更多回答（1 个）

Walter Roberson
Walter Roberson 2024-2-23

0 个投票

if frame1 == 1
Background1 = thisFrame1;
else
This does not define Background1 if frame1 ~= 1

4 个评论
显示 2更早的评论 隐藏 2更早的评论

LaraS
LaraS 2024-2-23
I see, how do you recommend I fix this? Would it be more straightforward if I just wrote a line that directly subtracts the background?
DGM
DGM 2024-2-23
It's not clear why the loop which increments through frames is inside the if-else and not the other way around.
LaraS
LaraS 2024-2-23
编辑：LaraS 2024-2-23
I actually tried correcting that while debugging (after posting this), but that didn't seem to help. Essentially what I'm trying to do is have the code update and adapt the background to each frame while it's running. It's really odd because it was running fine before when I was only running one video file. But I'm trying to update the script to run multiple files but it just throws this error about the undefined function now
DGM
DGM 2024-2-23
Well without knowing what the code or process is, there really isn't much I can suggest.

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Convert Image Type 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by