How to resize a specific part of an image?

Question

Ryan Parvar 2022-4-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1686564-how-to-resize-a-specific-part-of-an-image

评论： DGM 2025-3-25

Hello,

Does anyone know how I can resize a specific object in an image while the other dimensions are the same? Imagine we have a small circle inside of a big circle; how can I increase the size of the bigger circle while the smaller is constant, or how can I decrease the size of the smaller circle while the bigger circle is constant?

Thanks.

Here, I have created an example by magic select in paint 3D.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

DGM 2022-4-2

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1686564-how-to-resize-a-specific-part-of-an-image#answer_933224

编辑：DGM 2022-4-3

在 MATLAB Online 中打开

star.png

It would help if the image weren't mutilated by compression to begin with, and it depends what the requirements actually are. I think the ideal solution would simply be to reconstruct the objects as a set of polygons and then reconstruct a fresh raster image with the desired object geometry.

That said, I'm going to go somewhere in-between full vector reconstruction and direct image filtering. In this example, the image is reduced to a set of non-binarized masks so as to preserve any antialiasing. These masks are then transformed independently to a new geometry and then a composition-based approach is used to construct a new color image from the masks.

The latter part of this example uses tools from MIMT. This is not strictly necessary, but it is a convenience that I'm not in the mood to avoid today. I started by cleaning up one half of the supplied image (attached).

inpict = imread('star.png');
inpict = rgb2gray(inpict);
% these are the original colors
bgcolor = [148 149 153];
starcolor = [36 30 30];
hexcolor = [209 210 212];
% extract hexagon
hexmask = imdilate(inpict>180,ones(5));
hex = imadjust(inpict,stretchlim(inpict,0.1));
hex = hex.*uint8(hexmask);
% extract star
star = (255-inpict)-106;
star = imadjust(star,stretchlim(star,0.1));
star = star + uint8(hexmask)*255;
% configuration for rescaling objects
starscale = 0.8;
hexscale = 1.5;
staroffset = [10 0];
hexoffset = [10 0];
% create transformation matrix, transform star
sz = size(star);
starxfm = diag([starscale starscale 1]);
starxfm(3,1:2) = staroffset*starscale;
starxfm = affine2d(starxfm);
outview = affineOutputView(sz(1:2),starxfm,'boundsstyle','centeroutput');
star = imwarp(star,starxfm,'outputview',outview);
% create transformation matrix, transform hex
hexxfm = diag([hexscale hexscale 1]);
hexxfm(3,1:2) = hexoffset*hexscale;
hexxfm = affine2d(hexxfm);
outview = affineOutputView(sz(1:2),hexxfm,'boundsstyle','centeroutput');
hex = imwarp(hex,hexxfm,'outputview',outview);
% create flat RGB images for each object
starpict = colorpict([sz(1:2) 3],starcolor,'uint8');
hexpict = colorpict([sz(1:2) 3],hexcolor,'uint8');
background = colorpict([sz(1:2) 3],bgcolor,'uint8');
% compose images using star,hex as alpha
outpict = replacepixels(starpict,background,star);
outpict = replacepixels(hexpict,outpict,hex);
imshow(outpict)

These are results for differing values of starscale and hexscale:

The last example also demonstrates the use of independent offsets.

Since this image is constructed from scratch, the colors don't have to be the same as in the original image:

Similarly, the object stacking order doesn't have to be the same either:

I should point out that it's not strictly necessary to create flat images for the object overlays prior to composition. MIMT replacepixels() can also just accept the color tuple directly:

% create flat RGB image for the background only
background = colorpict([sz(1:2) 3],bgcolor,'uint8');
% compose images using star,hex as alpha
outpict = replacepixels(starcolor/255,background,star);
outpict = replacepixels(hexcolor/255,outpict,hex);

5 个评论
显示 3更早的评论隐藏 3更早的评论

DGM 2022-4-3

编辑：DGM 2022-4-3

在 MATLAB Online 中打开

For a hard-edged vector reconstruction of the primitives, consider the alternative example. This still uses MIMT tools. The image is reduced to binary masks which are analyzed to find the radii and centroids of the two objects. From this, ROI tools are used to create new binary masks with the specified scale and offset. From the new masks, an image is constructed by basic composition as in the above example.

inpict = imread('star.png');
inpict = rgb2gray(inpict);
sz = size(inpict);
% these are the original colors
bgcolor = [148 149 153];
starcolor = [36 30 30];
hexcolor = [209 210 212];
% extract objects as binary masks
star = imfill(inpict<50,'holes');
hex = inpict>180;
% find object center and radii
% note that i'm not looking for rotation angle
% i choose to assume that the polygons are ostensibly
% oriented such that one apex is directly at 90deg
S = regionprops(star,'centroid');
cs = S.Centroid;
[spy spx] = find(bwperim(star));
spr = sqrt(sum(([spx spy]-cs).^2,2));
rsmin = min(spr);
rsmaj = max(spr);
S = regionprops(hex,'centroid');
ch = S.Centroid;
[hpy hpx] = find(bwperim(hex));
hpr = sqrt(sum(([hpx hpy]-ch).^2,2));
rhmaj = max(hpr);
% configuration for rescaling objects
starscale = 1.5;
hexscale = 0.8;
staroffset = [0 0];
hexoffset = [0 0];
% use ROI tools to create new polygonal masks 
th = 90 + 360/10*(0:9);
r = repmat([rsmin rsmaj]*starscale,[1 5]);
[x y] = pol2cart(th.'/180*pi,r.');
imshow(star) % just a placeholder to fill the axes
Rs = images.roi.Polygon(gca);
Rs.Position = [x y]+cs+staroffset;
starmask = createMask(Rs);
th = 90 + 360/6*(0:5);
r = repmat(rhmaj*hexscale,[1 6]);
[x y] = pol2cart(th.'/180*pi,r.');
Rh = images.roi.Polygon(gca);
Rh.Position = [x y]+ch+hexoffset;
hexmask = createMask(Rh);
% compose new image
background = colorpict([sz(1:2) 3],bgcolor,'uint8');
outpict = replacepixels(starcolor/255,background,starmask);
outpict = replacepixels(hexcolor/255,outpict,hexmask);
imshow(outpict)

It's worth noting that this assumes that the polygons are regular. In the original image, the star is not regular. Similarly, this ignores any slight rotation the objects might have.

WANG 2025-3-25

Is there a way to maintain the size of the image after implementation?

DGM 2025-3-25

I don't understand. In both of the examples, the output image (outpict) has the same geometry (204x204) as the input image (inpict), regardless of the scale and offset parameters.

请先登录，再进行评论。