# Text skew detection and correction in image

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Yahya on 19 Nov 2022
Commented: Image Analyst on 22 Nov 2022
clc;clear all; close all;
a=imread('eq2.jpg');
figure;
imshow(a)
if size(a,3)==3
a=rgb2gray(a);
end
b=im2bw(a);
ar=imrotate_white(b,30);
figure
imshow(ar);
br=~(ar);
figure
imshow(br)
[r c]=size(b);
X=[];
for i=1:r
for j=1:c
if br(i,j)==1;
X=[X; i j];
end
end
end
size(X);
[coeff, score, latent]=pca(X);
figure;
biplot(coeff(:,1:2),'Scores',score(:,1:2),'VarLabels',{'v_1','v_2'});
r=sqrt((coeff(1,1))^2+(coeff(1,2))^2);
th=real(double(vpa(acos(coeff(1,1)/r)*180/pi)))
syms x
th=real(double(vpa(solve(x==th-90))))
rotatedImage=imrotate(br,-th);
figure
imshow(rotatedImage)
function rotated_image = imrotate_white(image, rot_angle_degree)
RA = imref2d(size(image));
tform = affine2d([cosd(rot_angle_degree) -sind(rot_angle_degree) 0; ...
sind(rot_angle_degree) cosd(rot_angle_degree) 0; ...
0 0 1]);
Rout = images.spatialref.internal.applyGeometricTransformToSpatialRef(RA,tform);
Rout.ImageSize = RA.ImageSize;
xTrans = mean(Rout.XWorldLimits) - mean(RA.XWorldLimits);
yTrans = mean(Rout.YWorldLimits) - mean(RA.YWorldLimits);
Rout.XWorldLimits = RA.XWorldLimits+xTrans;
Rout.YWorldLimits = RA.YWorldLimits+yTrans;
rotated_image = imwarp(image, tform, 'OutputView', Rout, 'interp', 'cubic', 'fillvalues', 255);
end
The output is
Rotate orgin image angle= 30
The answer is angle = 25.1508 !!!!
The angle must be 30 .
How do I solve this problem?
This problem appears to me in the rational equations only, but in the linear equations the angle is shown with high accuracy.
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### Answers (1)

cr on 19 Nov 2022
Edited: cr on 19 Nov 2022
In general, pattern maching is used. See estimateGeometricTransform()
But the result may not be exactly the angle it's rotated to.
##### 2 CommentsShowHide 1 older comment
Image Analyst on 22 Nov 2022
@Yahya Then why did you accept the answer?
In general, for an arbitrary, random set of blobs, there is no way to determine what is the "correct" skew and orientation angle.

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