I'm trying to convert some similar images from gif to png.
You can find two of the pictures here:
https://europa.eu/european-union/about-eu/history/1980-1989_en.
After converting the first gif (for the year 1981), you can see the background colour is the same as before, white, but for the second gif (for the year 1986), the background colour changed to pink. How to fix it?
Below is my code:
file_in = uigetfile('*.*', 'All Files', 'MultiSelect','on');
file_out = cellfun(#(x) cat(2, x(1:(length(x)-3)), 'png'),...
file_in, 'UniformOutput', false);
for i = 1: length(file_in)
[gif,map] = imread (file_in{i});
imwrite (gif, map, file_out{i}, 'Background', [0 0 0]);
end
Matlab have never change the image color after conversion. Thus, if you try to open the 'gif' or 'png' by imshow you will get the same result.
Whatever, if you want to change the background color to white use this code.
Related
I have problem with PNG sRGB rednering in Three.js. I have this piece of code where I am generation texture from SVG file:
(...) // managing whole SVG data which is long and not important as I will show below
window.temCanvas = document.createElement('canvas');
temCanvas.width = '2048';
temCanvas.height = '454';
window.temContext = temCanvas.getContext('2d', {colorSpace: "srgb", preserveDrawingBuffer: true});
temContext.clearRect(0, 0, 2048, 454);
temContext.drawImage(newTextureTopSVG, 0,0, 2048, 454);
var newTex1 = temCanvas.toDataURL("image/png"); // here should be info about sRGB?
Texture generated this way is showing different colors. All 0 and 255 values are showing correctly but when it is between i.e. rgb(0,128,255) should look like this:
but it is rendered as:
I saved png generated from SVG and compared it to similar png generated from graphic software, there is difference which I see in Notepad++, correct file contain this:
file which is rendering badly (after saving from canvas in Firefox) doesn't contain srgb text:
I suppose I have to add sRGB info here:
var newTex1 = temCanvas.toDataURL("image/png");
How to do it? But shouldn't it be always sRGB for PNG?
Maybe I am wrong and it is possible to force Three.js to show colors correctly by changing something in Material, Texture etc.?
I am using:
renderer.outputEncoding = sRGBEncoding;
I don't want to provide all data, I will edit this post if needed. It is way too long. Especially managing SVG data.
When using renderer.outputEncoding = sRGBEncoding;, sRGB encoded color textures must be configured like so:
texture.encoding = sRGBEncoding;
Otherwise the sRGB workflow is incomplete resulting in wrong colors.
I have a 4-channel image (.png, .tif) like this one:
I am using OpenCV, and I would like to add padding of type BORDER_REFLECT around the flower. copyMakeBorder is not useful, since it adds padding to the edges of the image.
I can add certain padding if I split the image in bgr + alpha and apply dilate with BORDER_REFLECT option on the bgr image, but that solution spoils all the pixels of the flower.
Is there any way to perform a selective BORDER_REFLECT padding addition on a ROI defined by a binary mask?
EDIT:
The result I expect is something like (sorry I painted it very quickly with GIMP) :
I painted two black lines to delimit the old & new contour of the flower after the padding, but of course those lines should not appear in the final result. The padding region (inside the two black lines) must be composed by mirrored pixels from the flower (I painted it yellow to make it understandable).
A simple python script to resize the image and copy the original over the enlarged one will do the trick.
import cv2
img = cv2.imread('border_reflect.png', cv2.IMREAD_UNCHANGED)
pad = 20
sh = img.shape
sh_pad = (sh[0]+pad, sh[1]+pad)
imgpad = cv2.resize(img, sh_pad)
imgpad[20:20+sh[0], 20:20+sh[1], :][img[:,:,3]==255] = img[img[:,:,3]==255]
cv2.imwrite("padded_image.png", imgpad)
Here is the result
But that doesn't look very 'centered'. So I modified the code to detect and account for the offsets while copying.
import cv2
img = cv2.imread('border_reflect.png', cv2.IMREAD_UNCHANGED)
pad = 20
sh = img.shape
sh_pad = (sh[0]+pad, sh[1]+pad)
imgpad = cv2.resize(img, sh_pad)
def get_roi(img):
cimg = img[:,:,3].copy()
contours,hierarchy = cv2.findContours(cimg,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)
#Remove the tiny pixel noises that get detected as contours
contours = [cnt for cnt in contours if cv2.contourArea(cnt) > 10]
x,y,w,h = cv2.boundingRect(cnt)
roi=img[y:y+h,x:x+w]
return roi
roi = get_roi(img)
roi2 = get_roi(imgpad)
sh = roi.shape
sh2 = roi2.shape
o = ((sh2[0]-sh[0])/2, (sh2[1]-sh[1])/2)
roi2[o[0]:o[0]+sh[0], o[1]:o[1]+sh[1], :][roi[:,:,3]==255] = roi[roi[:,:,3]==255]
cv2.imwrite("padded_image.png", imgpad)
Looks much better now
The issue has been already addressed and solved here:
http://answers.opencv.org/question/90229/add-padding-to-object-in-4-channel-image/
I am writing a function that generates a movie mimicking a particle in a fluid. The movie is coloured and I would like to generate a grayscaled movie for the start. Right now I am using avifile instead of videowriter. Any help on changing this code to get grayscale movie? Thanks in advance.
close all;
clear variables;
colormap('gray');
vidObj=avifile('movie.avi');
for i=1:N
[nx,ny]=coordinates(Lx,Ly,Nx,Ny,[x(i),-y(i)]);
[xf,yf]=ndgrid(nx,ny);
zf=zeros(size(xf))+z(i);
% generate a frame here
[E,H]=nfmie(an,bn,xf,yf,zf,rad,ns,nm,lambda,tf_flag,cc_flag);
Ecc=sqrt(real(E(:,:,1)).^2+real(E(:,:,2)).^2+real(E(:,:,3)).^2+imag(E(:,:,1)).^2+imag(E(:,:,2)).^2+imag(E(:,:,3)).^2);
clf
imagesc(nx/rad,ny/rad,Ecc);
writetif(Ecc,i);
if i==1
cl=caxis;
else
caxis(cl)
end
axis image;
axis off;
frame=getframe(gca);
cdata_size = size(frame.cdata);
data = uint8(zeros(ceil(cdata_size(1)/4)*4,ceil(cdata_size(2)/4)*4,3));
data(1:cdata_size(1),1:cdata_size(2),1:cdata_size(3)) = [frame.cdata];
frame.cdata = data;
vidObj = addframe(vidObj,frame);
end
vidObj = close(vidObj);
For your frame data, use rgb2gray to convert a colour frame into its grayscale counterpart. As such, change this line:
data(1:cdata_size(1),1:cdata_size(2),1:cdata_size(3)) = [frame.cdata];
To these two lines:
frameGray = rgb2gray(frame.cdata);
data(1:cdata_size(1),1:cdata_size(2),1:cdata_size(3)) = ...
cat(3,frameGray,frameGray,frameGray);
The first line of the new code will convert your colour frame into a single channel grayscale image. In colour, grayscale images have all of the same values for all of the channels, which is why for the second line, cat(3,frameGray,frameGray,frameGray); is being called. This stacks three copies of the grayscale image on top of each other as a 3D matrix and you can then write this frame to your file.
You need to do this stacking because when writing a frame to file using VideoWriter, the frame must be colour (a.k.a. a 3D matrix). As such, the only workaround you have if you want to write a grayscale frame to the file is to replicate the grayscale image into each of the red, green and blue channels to create its colour equivalent.
BTW, cdata_size(3) will always be 3, as getframe's cdata structure always returns a 3D matrix.
Good luck!
I am modifying images in matlab and I have a problem.
I need to separate the 3 channels of color and modify them separately.
I use this to obtain the three channels:
a = imread('./images/penguins.png');
colorlist = {'R','G','B'};
subplot(2,2,1);
imshow(a);
for k=1:3
subplot(2,2,k+1);
imshow( a(:,:,k));
title(colorlist{k});
end
a(:,:,k) is one color of the three. The problem is when I add the three vectors in one, to obtain the color image. I do this:
A=a(:,:,1)+a(:,:,2)+a(:,:,3)
figure; imshow(A);
But it dont works, it only show me a very highlight image, no a color image.
Anyone knows how can I recover the color image? Thanks for yout help^^
You are adding the values of the three layers instead of concatenating them in a 3D array.
Try this:
A= cat(3, a(:,:,1), a(:,:,2), a(:,:,3));
I should also note that you can edit the layers simply by indexing, say you want to switch the red and green components:
I1 = imread('http://i.stack.imgur.com/1KyJA.jpg');
I2=I1;
I2(:,:,1)=I1(:,:,2);
I2(:,:,2)=I1(:,:,1);
imshowpair(I1,I2, 'montage');
Now if I take your title literally, let's say you do want to add the three layers and display the result with a colormap, you can do:
A=a(:,:,1)+a(:,:,2)+a(:,:,3)
imagesc(A); axis image;
colorbar;
Results:
I have a grayscale image that only has the values 60 and 117. How can I convert the image to only black and white without graylevels?
I tried the matlab function gray2ind, but didn't get the expected output.
Thanks.
Try im2bw(img, level) with level = 0.5.
This is a matlab function that takes a grayscale image img, applies a threshold of level (a value between [0,1]) and returns a black and white image.
This function is part of the Image Processing Toolbox. Your case is simple enough that you could also try something like:
bwImg = false(size(img));
bwImg(img == 117) = true;
I edited the above to set values equal to false/true to more closely mimic Matlab's im2bw() which returns a matrix of logical values rather than ints.
2nd Edit: Modified the code block to reflect improvements suggested by #Amro