Why does plot quality reduce when plotting line and scatter together?

I am using plot3() and scatter3() together and the quality of the plot is reducing. The plot becomes a bit pixelated.

% Code snippets of what I am using
plot3(xSol{1}(first_seconds), omegaSol{1}(first_seconds), ESol{1}(first_seconds), 'LineWidth', 1.8, 'Color', PS.Purple2);
scatter3(x_FP(1, i), omega_FP(1, i), E_FP(1, i), 'Marker', 'o', 'SizeData', 60, 'MarkerFaceColor', PS.DRed2, 'MarkerEdgeColor', PS.Red4, 'MarkerFaceAlpha', MarkerAlpha);

Why is this happening? How can I get a smooth and high quality plot?

Problem picture:

Basically I want to have the dots with a certain alpha. plot3() does not allow that so I am using scatter3(). If there is another way of using 'o' Marker with plot3() and get alpha for them I can use that.

[KALYAN ACHARJYA]

Can you attach the complete code, so that we can reproduce the same plot?

[atharva aalok]

load('datafile.mat');
figure(2);
fig2_comps.fig = gcf;
%=================================================
% PLOT TIME SERIES

time_limit = 50;
upper_time_limit = 90;
first_seconds = tSol{1} < time_limit;
after_first_seconds = (tSol{1} > time_limit) & (tSol{1} < upper_time_limit);

% figure(1);
fig2_comps.p1 = plot3(xSol{1}(1), omegaSol{1}(1), ESol{1}(1), 'HandleVisibility', 'off', 'LineStyle', 'none', 'LineWidth', 1.5, 'Marker', 'o', 'MarkerSize', 6, 'MarkerFaceColor', PS.DBlue1, 'MarkerEdgeColor', PS.Purple2);
hold on
fig2_comps.p2 = plot3(xSol{1}(first_seconds), omegaSol{1}(first_seconds), ESol{1}(first_seconds), 'LineWidth', 1.8, 'Color', PS.Purple2);
fig2_comps.p3 = plot3(xSol{1}(after_first_seconds), omegaSol{1}(after_first_seconds), ESol{1}(after_first_seconds), 'LineWidth', 1.5, 'Color', PS.Green1);
grid on


MarkerAlpha_list = linspace(1, 0.2, length(x_FP(1, :)));

for i = 1:length(x_FP(1, :))
    
    MarkerAlpha = MarkerAlpha_list(i);
    fig2_comps.p4 = scatter3(x_FP(1, i), omega_FP(1, i), E_FP(1, i), 'HandleVisibility', 'off', 'Marker', 'o', 'SizeData', 60, 'MarkerFaceColor', PS.DRed2, 'MarkerEdgeColor', PS.Red4, 'MarkerFaceAlpha', MarkerAlpha);
    fig2_comps.p5 = scatter3(x_FP(2, i), omega_FP(2, i), E_FP(2, i), 'HandleVisibility', 'off', 'Marker', 'o', 'SizeData', 60, 'MarkerFaceColor', PS.DBlue2, 'MarkerEdgeColor', PS.Blue4, 'MarkerFaceAlpha', MarkerAlpha);
    
end

legend('location', 'northwest');

[KALYAN ACHARJYA]

You have 20 samples only, as per attached data.

[atharva aalok]

No, 20 is the number of circles appearing.

I am talking about the pixelation of the line.

[atharva aalok]

For some reason this pixelation is only happening when displaying.

When I save the figure with 600dpi no pixelation happens.

[KALYAN ACHARJYA]

OK

Answer 1

[Bjorn Gustavsson]

The painters-renderer that produces vector-format output, like eps doesn't understand alpha-type transparency. Therefore when you have plots utilizing alpha-mapped transparent objects you will get figures saved with the opengl renderer - which understands transparency but produces pixel-based images. There is (as far as I know) nothing much we can do about that.

Hope this clarifies the issue.