Transparency causes nonsmooth lines

When I set transparency in the figure, the original smooth line becomes nonsmooth.

[x,y] = meshgrid(-2:.2:2);

z = x.*exp(-x.^2-y.^2);

a = gradient(z);

figure; surf(x,y,z,'AlphaData',a,'FaceAlpha','flat','FaceColor','blue');

figure; surf(x,y,z)

[KALYAN ACHARJYA]

What is your question?

[bai da]

Jan has pointed out the problem. The line becomes nonsmooth after I set transparency to the figure

Answer 1

[Jan]

Transparency requires the OpenGL renderer. The line-smoothing requires the Painters renderer. As far as I can see, you observe the expected behavior.

[bai da]

Thanks! Are there any trick to avoid this dilemma?

[Jan]

"Dilemma" means that it is not a "lemma", or in other words: It cannot be decided. This implies, that you cannot avoid it, because it is the nature of the different renderers.

But you can reduce the effects or find a work-around. It depends on what you want to do with the displayed graphics. Does your problem concerns the output to the screen or do you want to export a smoothed graphics file? KALYAN ACHARJYA asked already, what your question is.

Which Matlab version are you using and do you have the Image Processing toolbox?

[bai da]

Yes， I want to export a smoothed file. I'm using version 2017a. I have the image processing toolbox

[Jan]

Try this:

RGB = AntiAlias(gcf, 4, 'lanczos3');
imwrite(RGB, 'File.png');

Using this function:

function Out = AntiAlias(FigH, K, Method)
% Anti-aliasing of a figure
% Reply = AntiAliasFig(FigH, K)
%   FigH: Figure handle.
%   K:    Integer subsampling factor >= 1: The created pictures uses a K-times
%         higher resolution.
%         For K = 1 the output equals the original picture.
%   Method: See Method of IMRESIZE: E.g. 'lanczos3'
%
% OUTPUT:
%   Reply: RGB data are replied as [M x N x 3] UINT8 array.
%
% Tested: Matlab/64 9.1, Win10
% Author: Jan Simon, Heidelberg, (C) 2018

% Initialize: ==================================================================
screen_DPI  = get(groot, 'ScreenPixelsPerInch');

% Do the work: =================================================================
% Wanted resolution as string:
ResolutionStr = sprintf('-r%d', round(screen_DPI * K));

% Prepare figure for hardcopy:
drawnow;
fig_Renderer     = get(FigH, 'Renderer');
fig_Paperposmode = get(FigH, 'PaperPositionMode');
fig_PaperOrient  = get(FigH, 'PaperOrientation');
fig_Invhardcopy  = get(FigH, 'InvertHardcopy');
set(FigH, ...
   'PaperPositionMode', 'auto', ...
   'PaperOrientation',  'portrait', ...
   'InvertHardcopy',    'off');

% Create hard copy in high resolution: -----------------------------------------
% Simulate PRINT command (save time for writing and reading image file):
% Set units of axes and text from PIXELS to POINTS to keep their sizes
% independent from from the output resolution:
% See: graphics/private/preparehg.m
root_SHH     = get(groot, 'ShowHiddenHandles');
set(groot, 'ShowHiddenHandles', 'on');
text_axes_H  = [findobj(FigH, 'Type', 'axes'); ...
   findobj(FigH, 'Type', 'text')];
pixelObj     = findobj(text_axes_H, 'Units',     'pixels');
fontPixelObj = findobj(text_axes_H, 'FontUnits', 'pixels');
set(pixelObj,     'Units',     'points');
set(fontPixelObj, 'FontUnits', 'points');

fig_ResizeFcn = get(FigH, 'ResizeFcn');
set(FigH, 'ResizeFcn', '');

% Get image as RGB array:
high = print('-RGBImage', ResolutionStr);

% Restore units of axes and text objects, and EraseMode:
set(pixelObj,     'Units',     'pixels');
set(fontPixelObj, 'FontUnits', 'pixels');
set(groot, 'ShowHiddenHandles', root_SHH);
set(FigH, 'ResizeFcn', fig_ResizeFcn);

% Restore properties of the original image:
set(FigH, ...
   'InvertHardcopy',    fig_Invhardcopy, ...
   'PaperPositionMode', fig_Paperposmode, ...
   'PaperOrientation',  fig_PaperOrient, ...
   'Renderer',          fig_Renderer);

% Create the low resolution data and axes properties:
try
   low = imresize(high, 1 / K, Method);  % Hide from CheckSyntax
catch ME
   if isempty(which('imresize'))
      error(['*** %s: Signal-Processing-Toolbox is required.', ...
         char(10), '%s'], mfilename, Mode, ME.message);
   else
      error(['*** %s: Unknown [Mode]: [%s]', ...
         char(10), '%s'], mfilename, Mode, ME.message);
   end
end

% Limit range of data:
% Slightly slower: lowres = max(min(lowres, 1), 0);
if isa(low, 'double')
   low(low < 0) = 0;
   low(low > 1) = 1;
end

Out = low;

end

[bai da]

Thank you very much! It works! It also works in Linux (Ubuntu).

Answer 2

[Indrajit Wadgaonkar]

Did this issue get resolved? What is the solution if I need transparency as well as smooth lines?