How to measure spray penetration length and spray area?

Dear community member,

In order to continue processing data for the experiment results, I have to calculate the spray penetration length based on the spray image. Previously I got the code from Image Analyst to calculate the spray cone angle as a reference.

My current idea is to set the spray plume segmentation from the binary image first in order to define the spray boundary, then start to measure the along the Y axis from spray origin to the farthest point of the spray (Please refer to the attach. 1 images)

How I can proceed after getting the initial binary image? I tried to use bwboundaries function but didn't manage to get it right.

Then, if the spray plume segmentation is fully defined, can the spray area be calculated also? It would be very very helpful if these two cases can be solved.

Please kindly guide me to resolve this problem.

The image that will be processed is also attached.

Thank you again for your kindness and support.

[Daniel Bengtson]

If you already have a clean binary image such as the one shown as "initial binary image" on that subplot, couldn't you just sum the the masked pixels to find area, then find the furthest point on the spray as just the last row that contains a portion of your mask?

Assuming that your mask is a 2d array of 0s and 1s

pixArea = sum(imBinary,'all'); % total count of all masked pixels in the image

pixVertLoc = sum(imBinary,2); % number of pixels in each row of the image that are within the mask
pixMaxDist = find(pixVertLoc > 0,1,'last'); %finds last row that contains a portion of the mask

You will still have to figure out the transformations to convert pixel count and location to real world area and distance.

[I Komang Gede Tryas Agameru Putra]

Dear Daniel,

Thanks for the advice! I will try it and give the update.

Best Regards.

[I Komang Gede Tryas Agameru Putra]

Dear Daniel,

I didn't manage to insert the code that you gave. Could you please enligthen me where do I put that code?

I've attached the the code in the attachment.

Thank you again for your support.

[I Komang Gede Tryas Agameru Putra]

I think the issue has been resolved, thank you very much for giving the insight.

Best Regards!

Answer 1

[Image Analyst]

There are several ways you can determine the starting and ending rows. I think the fastest is just this

[blobRows, blobColumns] = find(binaryImage);
topRow = min(blobRows)
bottomRow = max(blobRows)

You could also use regionprops and ask for the bounding box.

props = regionprops(binaryImage, 'BoundingBox');
topRow = props.BoundingBox(2) + 0.5
bottomRow = topRow + props.BoundingBox(4) - 1

[I Komang Gede Tryas Agameru Putra]

Dear Image Analyst,

Thank you for giving the alternative solution.

I have attached the code and the spray picture that I am currently using.

The problem occurs when the injected spray is exceeding the red circle area, so the number of all pixel area is not fully covered. (Please see the attached images)

Could you please help me to solve this problem?

Thank you for your support.

Best Regards.

[Image Analyst]

Expand the radius of the circle so that it goes down to the bottom. Then, to get rid of the nozzle at the top just erase all lines up to there. Something like

binaryImage(1:240, :) = 65535; % Set to bright white.

[I Komang Gede Tryas Agameru Putra]

I changed the radius but I am not sure which one to delete, could you give advice?

Thank you for your support

function grayImage = CircleMaskImage(grayImage)
% Get the size of the image.
[imageSizeY, imageSizeX, numberOfColorChannels] = size(grayImage);
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
[columnsInImage, rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = imageSizeX / 2;
centerY = imageSizeY / 2;
radius = 170;
% Display circle in the overlay above the current axes.
viscircles([centerX, centerY], radius, 'Color', 'r');
% Here is where we actually create the mask.
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
% image(circlePixels) ;
% colormap([0 0 0; 1 1 1]);
% title('Binary image of a circle');
% Set image outside the circle to some very bright value 
% so it won't be selected when we do a threshold for dark stuff.
grayImage(~circlePixels) = 65535;

end

[Image Analyst]

Row 41 looks like it should do it to erase the nozzle:

% Do an closing to smooth out the edges.
se = strel('disk', 3, 0);
binaryImage = imclose(binaryImage, se);
%---------------------------------------------------------------------------
% Fill any holes that might be present
binaryImage = imfill(binaryImage, 'holes');

% Erase nozzle.
binaryImage(1:41, :) = false;
%---------------------------------------------------------------------------
% Extract the blob with the largest area.
numberToExtract = 1;
binaryImage = bwareafilt(binaryImage, numberToExtract);
% Display the image.
subplot(2, 3, 3);
imshow(binaryImage);
axis on;
title('Biggest Blob, Final Mask', 'FontSize', fontSize);
drawnow;

[I Komang Gede Tryas Agameru Putra]

Dear Image Analyst,

Thank you for solving the problem! It worked out smooth.

Thank you very much for your support.

Best Regards.

[I Komang Gede Tryas Agameru Putra]

Dear Image Analyst,

Sorry for asking you further question.

I want to do a batch image processing and it will be contained by 100 pictures in each folder.

These two codes will be the main code, then I would like to gather all the 100 images data based on this code.

I tried to use Image Batch Processor apps on the matlab, and I am confused how to merge the code.

The question is, how can I merge below code if I want to do the batch image processing?

Please kindly help me to solve this matter.

Thank you for your support

I took reference using this source https://kr.mathworks.com/matlabcentral/fileexchange/89867-getting-started-with-image-processing-example-files?s_eid=PSM_15028

function results = calculateArea(I)

% Segment

BW = createMask(I);

% Area in pixels

props = regionprops("table",BW,"Area");

areaPixels = sum(props.Area);

% Area in km^2

px2km = (51/20)^2;

areaKmSq = round(areaPixels*px2km);

% Format into structure

results.BW = BW;

results.areaKmSq = areaKmSq;

[Image Analyst]

I would just use one of the code snippets in the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files?

[I Komang Gede Tryas Agameru Putra]

Dear Image Analyst,

Thank you for giving the insight!

Best Regards.