I am working on creating an image splicing detection software so I need to divide the image into non-overlapping blocsk and apply Discrete Meyer Wavelet Transform on each block of the image
I have tried the blockproc function to do that but I got no result:
I = imread('pears.png');
fun = #(block_struct)...
dwt2(block_struct.data,'dmey');
C = blockproc(I,[64 64],fun);
So how can I access the [cA,cH,cV,cD] of dwt2 using the above code?
blockproc assumes that you are outputting an actual image. You cannot use this for multiple outputs. If you truly want this to work with blockproc, you will unfortunately need to call blockproc four times, with each time extracting the different set of coefficients for the directions. Also note that the 2D DWT only works for grayscale images, so you need to convert to grayscale before actually doing any processing. The pears image you've chosen is a colour / RGB image.
I'd like to reference this post on how to select the Nth output given an input function: How do I get the second return value from a function without using temporary variables?. You will need to save this code to a file called nth_output.m, which allows you to programatically extract all output variables from a function and choose only one output.
function value = nth_output(N,fcn,varargin)
[value{1:N}] = fcn(varargin{:});
value = value{N};
end
Simply omitting the extra output arguments when you call the function only gives you the first output, which is what your blockproc code is doing. Once you do that, it's a matter of creating 4 anonymous functions to capture each output from dwt2, and running blockproc 4 times. Make sure you specify which output you want for each of the anonymous functions, so 1 up to 4 and you simply provide a handle to the function you want to run in addition to the input arguments that go into the function.
Therefore, try something like this:
I = rgb2gray(imread('pears.png'));
fun1 = #(block_struct) nth_output(1, #dwt2, block_struct.data,'dmey');
fun2 = #(block_struct) nth_output(2, #dwt2, block_struct.data,'dmey');
fun3 = #(block_struct) nth_output(3, #dwt2, block_struct.data,'dmey');
fun4 = #(block_struct) nth_output(4, #dwt2, block_struct.data,'dmey');
I = rgb2gray(I);
cA = blockproc(I,[64 64],fun1);
cH = blockproc(I,[64 64],fun2);
cV = blockproc(I,[64 64],fun3);
cD = blockproc(I,[64 64],fun4);
cA, cH, cV, and cD contain the DWT coefficients you need for each set of directions.
[EDIT2] I am using the code below to plot a real time signal from serial port.
The issue I have is that the plot lags a lot even though I am not replotting the whole screen.
How can I speed up the process?
function timerCallback(~,~,hObject)
handles = guidata(hObject);
[r,w]=size(handles.y);
if isfield(handles,'s')
try
readasync(handles.s);
n = handles.s.BytesAvailable;
if n > 0
in = fscanf(handles.s,'%d');
handles.y=[handles.y,in];
guidata(hObject,handles);
set(handles.h,'yData',(handles.y-99)*26/855);
startSpot = (w)-1000;
axis([ startSpot, (w+50), 0 , 30 ]);
drawnow
end
catch
end
end
Timer is set to fixedRate at 0.001s.
[EDIT2]
I have moved the plot line outside the timer callback. I can't barely see any difference in performance.
I created an matrix using some calculation.I saved it in the BMP format.But when I am reading it back in MATLAB,the content of it changes totally.Only where value is 0 is correct.All other pixels are having values 255.Why is this.How to solve this??
It is showing image correctly when imsec command is used
for i=1:length(pixel_matrix)
pixel=char(pixel_matrix(i));
r=7;
pixel_value=0;
for j=1:4
s=r-1;
if(pixel(j)=='A')
temp_bin=0;
elseif(pixel(j)=='B')
temp_bin=(2^r)+(2^s);
elseif(pixel(j)=='C')
temp_bin=(2^s);
elseif(pixel(j)=='D')
temp_bin=(2^r);
end
pixel_value=pixel_value+temp_bin;
r=r-2;
end
pixel_row(i)=pixel_value;
end
i=1;
j=1;
for m=1:length(pixel_row)
pixel_value(i,j)=pixel_row(m);
j=j+1;
if(j==65)
i=i+1;
j=1;
end
end
for i=1:64
for j=1:64
picture(i,j)=uint8(pixel_value(i,j));
end
end
imwrite(picture,'C:\Users\XXX\Desktop\pic.bmp');
aaaa=imread('C:\Users\XXX\Desktop\pic.bmp');
the problem is most likely that you are filling picture with uint8 values, but when not specified otherwise, images in MatLab are doubles between 0 and 1. Try using the Map option for imwrite or norm the values of pixel_value(i,j) to fit them between 0 and 1 like this:
%...
for i=1:64
for j=1:64
picture(i,j)=pixel_value(i,j)/255; %<- Norm things here...
end
end
I have a load of data in 100 .sdf files (labelled 0000.sdf to 0099.sdf), each of which contain a still image, and I'm trying to produce a .gif from these images.
The code I use to plot the figure are (in the same directory as the sdf files):
q = GetDataSDF('0000.sdf');
imagesc(q.data');
I've attempted to write a for loop that would plot the figure and then save it with the same filename as the sdf file but to no avail, using:
for a = 1:100
q=GetDataSDF('0000.sdf');
fh = imagesc(q.dist_fn.x_px.Left.data');
frm = getframe( fh );
% save as png image
saveas(fh, 'current_frame_%02d.jpg');
end
EDIT: I received the following errors when trying to run this code:
Error using hg.image/get
The name 'Units' is not an accessible property for an instance of class 'image'.
Error in getframe>Local_getRectanglesOfInterest (line 138)
if ~strcmpi(get(h, 'Units'), 'Pixels')
Error in getframe (line 56)
[offsetRect, absoluteRect, figPos, figOuterPos] = ...
Error in loop_code (line 4)
frm = getframe( fh );
How do I save these files using a for loop, and how do I then use those files to produce a movie?
The reason for the error is that you pass an image handle to getframe, but this function excpects a figure handle.
Another problem is that you always load the same file, and that you saveas will not work for gifs. (For saving figures as static images, maybe print is the better option?)
I tried to modify my own gif-writing loop so that it works with your data. I'll try to be extra explicit in the comments, since you seem to be starting out. Remember, you can always use help name_of_command to display a short Matlab help.
% Define a variable that holds the frames per second your "movie" should have
gif_fps = 24;
% Define string variable that holds the filename of your movie
video_filename = 'video.gif';
% Create figure 1, store the handle in a variable, you'll need it later
fh = figure(1);
for a = 0:99
% Prepare file name so that you loop over the data
q = GetDataSDF(['00' num2str(a,'%02d') 'sdf']);
% Plot image
imagesc(q.dist_fn.x_px.Left.data');
% Force Matlab to actually do the plot (it sometimes gets lazy in loops)
drawnow;
% Take a "screenshot" of the figure fh
frame = getframe(fh);
% Turn screenshot into image
im = frame2im(frame);
% Turn image into indexed image (the gif format needs this)
[imind,cm] = rgb2ind(im,256);
% If first loop iteration: Create the file, else append to it
if a == 0;
imwrite(imind,cm,video_filename,'gif', 'Loopcount',inf);
else
imwrite(imind,cm,video_filename,'gif','WriteMode','append','DelayTime',1/gif_fps);
end
end
One more note: When the size of the data is the same for each plot, it makes sense to only use the plot(or in this case, imagesc) command once, and in later loop iterations replace it with a set(ah,'Ydata',new_y_data) (or in this case set(ah,'CData',q.dist_fn.x_px.Left.data'), where ah is a handle of the plot axes (not the plot figure!). This is orders of magnitude faster than creating a whole new plot in each loop iteration. The downside is that the scaling (here, the color-scaling) will be the same for each plot. But in every case that I have worked on so far, that was actually desirable.
I would like to create an animation which enables the user to go backward and forward through the steps of simulation.
An animation has to simulate the iterative process of channel decoding (a receiver receives a block of bits, performs an operation and then checks if the block corresponds to parity rules. If the block doesn't correspond the operation is performed again and the process finally ends when the code corresponds to a given rules).
I have written the functions which perform the decoding process and return a m x n x i matrix where m x n is the block of data and i is the iteration index. So if it takes 3 iterations to decode the data the function returns a m x n x 3 matrix with each step is stired.
In the GUI (.fig file) I put a "decode" button which runs the method for decoding and there are buttons "back" and "forward" which have to enable the user to switch between the data of recorded steps.
I have stored the "decodedData" matrix and currentStep value as a global variable so by clicking "forward" and "next" buttons the indices have to change and point to appropriate step states.
When I tried to debug the application the method returned the decoded data but when I tried to click "back" and "next" the decoded data appeared not to be declared.
Does anyone know how is it possible to access (or store) the results of the functions in order to enable the described logic which I want to implement in Matlab GUI?
Ultimately, this is a scoping of variables problem.
Global variables is rarely the right answer.
This video discusses the handles structure in GUIDE:
http://blogs.mathworks.com/videos/2008/04/17/advanced-matlab-handles-and-other-inputs-to-guide-callbacks/
This video discusses sharing of variables between GUIs and could apply to a single GUI problem also.
http://blogs.mathworks.com/videos/2005/10/03/guide-video-part-two/
The trick is to use nested functions so that they share the same workspace. Since I already started with an example in your last question, now I'm simply adding GUI controls to enable going forward/backward interactively, in addition to play/stop the animation:
function testAnimationGUI()
%# coordinates
t = (0:.01:2*pi)'; %# 'fix SO syntax highlight
D = [cos(t) -sin(t)];
%# setup a figure and axis
hFig = figure('Backingstore','off', 'DoubleBuffer','on');
hAx = axes('Parent',hFig, 'XLim',[-1 1], 'YLim',[-1 1], ...
'Drawmode','fast', 'NextPlot','add');
axis(hAx, 'off','square')
%# draw circular path
line(D(:,1), D(:,2), 'Color',[.3 .3 .3], 'LineWidth',1);
%# initialize point
hLine = line('XData',D(1,1), 'YData',D(1,2), 'EraseMode','xor', ...
'Color','r', 'marker','.', 'MarkerSize',50);
%# init text
hTxt = text(0, 0, num2str(t(1)), 'FontSize',12, 'EraseMode','xor');
i=0;
animation = false;
hBeginButton = uicontrol('Parent',hFig, 'Position',[1 1 30 20], ...
'String','<<', 'Callback',#beginButton_callback);
hPrevButton = uicontrol('Parent',hFig, 'Position',[30 1 30 20], ...
'String','<', 'Callback',#previousButton_callback);
hNextButton = uicontrol('Parent',hFig, 'Position',[60 1 30 20], ...
'String','>', 'Callback',#nextButton_callback);
hEndButton = uicontrol('Parent',hFig, 'Position',[90 1 30 20], ...
'String','>>', 'Callback',#endButton_callback);
hSlider = uicontrol('Parent',hFig, 'Style','slider', 'Value',1, 'Min',1,...
'Max',numel(t), 'SliderStep', [10 100]./numel(t), ...
'Position',[150 1 300 20], 'Callback',#slider_callback);
hPlayButton = uicontrol('Parent',hFig, 'Position',[500 1 30 20], ...
'String','|>', 'Callback',#playButton_callback);
hStopButton = uicontrol('Parent',hFig, 'Position',[530 1 30 20], ...
'String','#', 'Callback',#stopButton_callback);
%#----------- NESTED CALLBACK FUNCTIONS -----------------
function beginButton_callback(hObj,eventdata)
updateCircle(1)
end
function endButton_callback(hObj,eventdata)
updateCircle(numel(t))
end
function nextButton_callback(hObj,eventdata)
i = i+1;
if ( i > numel(t) ), i = 1; end
updateCircle(i)
end
function previousButton_callback(hObj,eventdata)
i = i-1;
if ( i < 1 ), i = numel(t); end
updateCircle(i)
end
function slider_callback(hObj, eventdata)
i = round( get(gcbo,'Value') );
updateCircle(i)
end
function playButton_callback(hObj, eventdata)
animation = true;
while animation
i = i+1;
if ( i > numel(t) ), i = 1; end
updateCircle(i)
end
end
function stopButton_callback(hObj, eventdata)
animation = false;
end
function updateCircle(idx)
set(hSlider, 'Value', rem(idx-1,numel(t))+1) %# update slider to match
set(hLine,'XData',D(idx,1), 'YData',D(idx,2)) %# update X/Y data
set(hTxt,'String',num2str(t(idx))) %# update angle text
drawnow %# force refresh
if ~ishandle(hAx), return; end %# check valid handle
end
%#-------------------------------------------------------
end
You might find the slider functionality a bit buggy, but you get the idea :)