为什么在此带有export_fig的Matlab Polar演示文稿中存在间隙? [英] Why is there Gap in this Matlab Polar presentation with export_fig?

问题描述

在origo(0,0)到(1,0)的直线上产生间隙的代码，如果C尺寸达到无穷大，该间隙似乎为零；但是，对于任何大小的C，我都无法将其缩小到足够小，因此，我认为该伪像可能是由Matlab图形的内部特征或图像数据本身(AnderBiguri)引起的，因为对于img=imread('peppers.png')来说似乎不会发生. 制作图像的代码，通过 export_fig 存储并映射从笛卡尔到极地发生伪像的地方

Code which yields a gap at the line from origo (0,0) to (1,0), which seems to reach zero if C dimensions reaches infinity; however, I cannot get it small enough with any sizes of C so I think the artifact can be caused by Matlab figure internal features or image data itself (AnderBiguri) because it does not seem to occur for img=imread('peppers.png'). Code which makes the image, stores it by export_fig and maps it from Cartesian to Polar where the artifact occurs

close all; clear all; clc;

%% Make image
f1=figure;
hax=axes(f1);
x = rand(1,6);
y = exp(rand(1,181));
C = rand(3613,3613);
imagesc(hax, x, y, C); 
box(hax, 'off');
axis(hax, 'off');
set(hax, 'yTickLabel', []);
set(hax, 'xTickLabel', []); % for polar presentation
set(hax, 'Ticklength', [0 0]); % http://stackoverflow.com/a/15529630/54964
filename='/home/masi/Images/testi';
% by default, export_fig has cropping
[img, alpha] = export_fig(filename, '-png', '-native', '-q101', '-a1', '-m1', '-RGB', '-nofontswap', '-dpng', hax);
close all; 

%% Read Image
img=imread('/home/masi/Images/testi.png');
% http://stackoverflow.com/a/7586650/54964
[h,w,~] = size(img);
s = min(h,w)/2; % have here .../1, some phenomenon occurs
[rho,theta] = meshgrid(linspace(0,s-1,s), linspace(0,2*pi,s));
[x,y] = pol2cart(theta, rho);
z = zeros(size(x));
subplot(121), imshow(img)
subplot(122), warp(x, y, z, img)
view(2), axis square tight off

图. 1 size(C)=[3613 3613]时输出， 图2 size(C)=[36130 36130]

Fig. 1 Output when size(C)=[3613 3613], Fig. 2 Output when size(C)=[36130 36130]

Matlab:2016a
Export_fig:16年8月8日版本
操作系统:Debian 8.5 64位
Linux内核:4.6个反向端口
硬件:华硕Zenbook UX303UA

Matlab: 2016a
Export_fig: 08/08/16 version
OS: Debian 8.5 64 bit
Linux kernel: 4.6 of backports
Hardware: Asus Zenbook UX303UA

推荐答案

我对此进行了快速浏览，是的，正在发生一些奇怪的事情.问题在于您的图像周围有边框，在绘制image时似乎没有边框，因为它的颜色与背景相同！

I had a quick look at this, and yeah, something strange is happening. The problem is that you have a border around your image, a border that does not seem to be there when plotting the image, because its the same color as the background!

如果您使用

C = rand(100,100);

，然后在用imagesc而不是imshow加载后对其进行绘制，您可以看到以下内容:

and then plot it after loading it with imagesc instead of imshow you can see this:

这就是它被转换为极坐标图中缺少的谱带的原因.如果仅删除大小为1的图像周围的边框，则会得到完整的图.

That is what it gets translated to an band missing in the polar plot. If you just remove the border around the image of size 1, you'll get a full plot.

我最好的猜测是，在export_fig内的某个地方，或者您的语句% by default, export_fig has cropping为假，或者裁剪有一些小错误，并且距背景1个像素.

My best guess is that somewhere inside export_fig either your statement % by default, export_fig has cropping is false or the cropping has some minor bug and takes 1 pixel from the background.

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