imnoise does not work as expected

2013 1 24
1 个回答
回答已采纳
4 次查看（30 天）

0 个投票

imnoise(a, 'gaussian', mean, var) seems simple enough in concept: add a Gaussian distribution of noise to an image. However, it does not recover the values expected.
Try: >> a = zeros(16, 16); b = imnoise(a, 'gaussian', 0, 0.1); >> mean(b(:)) ans = 0.1262 >> std(b(:))^2 ans = 0.040
The mean is not zero! The variance is not 0.1!
I can't figure out why the imnoise code produces this result. The code snippet is below.
switch code case 'gaussian' % Gaussian white noise b = a + sqrt(p4)*randn(sizeA) + p3;
If a = 0 and p3 = 0, then the result should have a mean value of zero.
Answers?

请先登录，再回答此问题。

 采纳的回答

Steve Eddins
Steve Eddins 2013-1-24

0 个投票

imnoise clips the output to the range [0,1].
>> min(b(:))
ans =
0

2 个评论
显示 无 隐藏 无

Brian
Brian 2013-1-24
Ok. Now try something that should address this:
>> a = ones(1024); b = imnoise(a, 'gaussian', 0, 0.1); >> mean(b(:) - 1) ans = -0.1261 ??? shouldn't this be zero?
>> std(b(:) - 1) ans = 0.1844 ??? shouldn't this be sqrt(0.1)?
Brian
Brian 2013-1-24
You really need to add this to your documentation of your demos. I did not expect
I = im2double(imread('cameraman.tif'));
to normalize the image [0,1]. If you look at the documentation for im2double, it states "rescaling the data if necessary". That is subjective. Necessary for what?
The best documentation has mathematical formulas and references.

请先登录，再进行评论。

更多回答（0 个）

类别

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

产品

标签

Community Treasure Hunt

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

Start Hunting!

Translated by