I was reading an article and they work on the gray image from green channel. They work with retina images and detect blood vessels on it.
My questions are that:
What does 'gray image from green channel' mean?
How can I get this gray image from green channel?
What is the difference between the gray image which is result of this matlab code I = rgb2gray(RGB) and gray image from green channel?
Thank you.
Just for fun, you can do it with ImageMagick which is installed on most Linux/Unix boxes and available for free for Windows and OSX like this:
Starting with this image:
convert plant.jpg -separate -delete 0,2 out.jpg
That separates the image into Red, Green and Blue channels, then deletes the Red and Blue channels leaving just the Green channel which then becomes a monochromatic (grey) representation of the amount of green in each pixel - so the green of the plant shows up the brightest/lightest.
Related
i am working on a project where i need to do some image processing, where i am not an expert.
I have an image obtained from QEMSCAN technology,as you can see here pink pixels represent the existence of the gold. there are 3 types of gold, type 1 where the connected pink pixels are surrounded with white ones. type 2 when the connected pink pixels are surrounded with white and another color.
type 3 where the pink area is connected with another colors except white.
I did some morphological image processing to isolate each area containing gold, but I'm blocked right now how i can determine to which type belong each pink area
thanks in advance
determine the type of gold
image
Here's a possible approach:
make all the pink pixels white and everything else black
do a dilation and find the coordinates of the additional pixels
check the colour(s) of the additional pixels in the original image
Since it is hard to me to explain what I'm trying to do, I'm gonna show you this page to show you what I'm trying to reproduce and understand:
https://optifine.net/showCape?colTop=FF0000&colBottom=00FF00&colText=0000FF&colShadow=FD0000
which outputs this:
and this one https://optifine.net/showCape?colTop=FF00FF&colBottom=0034EE&colText=000000&colShadow=FF00E2 outputs this:
You can modify the hexadecimal colors, basically I'm trying to reproduce something like that. Basically you modify the colors and it gives you an image at the end with the colors you used.
I've tried to make the "possible" template that could be used on the page on Photoshop which can be downloaded here, it is a .psd file, that's because of the Alpha Channel, which I'm not even sure if done correctly. But based of these RGBA channels it should be possible to change the color. Can be downloaded here: https://workupload.com/file/4xYkgQMk
So what I know so far is that there is a template with RGBA channel. Each channel is indepedent so it apperantly doesn't matter if it's RGBA and at the end R channel is used to turn into another color other than red, where I'm not sure about that.
I've asked the developer he told me that these channels get interpolated with the real color after that, probably the one you choose.
Basically what is happening at showCape? and its URL parameters is that, lets assume colTop got assigned to the red channel then when you put a color in colTop it will get a fixed color that it will encode or something.
So the template has 4 Channels RGBA that can be made in Photoshop, the white color 255,255,255 means basically full and the black 0,0,0 means complete black. Like that you can setup brightness scales for the template.
I just don't know how to modify the channels and I don't understand how to use the Alpha channels properly or set them up.
I'm also not sure in which programming languages it is possible to peform and if you can test the template directly in something like Photoshop. Is it possible to do it in JavaScript or something to easy setup and if not on what then, to test it fast?
Ok, so here's how you can generate that sort of thing with ImageMagick, which is included in most Linux distros and is available for macOS and Windows. Note that there are Python, PHP, node.js and other bindings available.
First, generate a red rectangle:
magick -size 200x150 xc:red red.png
Now see how to do the same thing with hex codes:
magick -size 200x150 xc:"#ff0000" red.png
Now, draw a red rectangle with a blue one on top:
magick -size 200x150 xc:red -fill blue -draw "rectangle 10,10 80,140" redandblue.png
Now make the blue transparent:
magick -size 200x150 xc:red -fill blue -draw "rectangle 10,10 80,140" -transparent blue redandtrans.png
Now make a gradient from lime green to magenta:
magick -size 200x150 gradient:lime-magenta gradient.png
Now overlay the red rectangle with transparent window onto the gradient:
magick gradient.png redandtrans.png -composite overlay.png
Now add text:
magick overlay.png -fill "#0000ff" -pointsize 16 -draw "text 90,40 'Coloured text'" result.png
And now do the whole thing again, in one go:
magick -size 200x150 gradient:lime-magenta \
\( xc:red -fill blue -draw "rectangle 10,10 80,140" -transparent blue \) \
-composite \
-fill "#0000ff" -pointsize 16 -draw "text 90,40 'Coloured text'" result.png
Now you have provided a template, I can separate out the channels with ImageMagick like this and append them side-by-side with Red channel on the left, then Green, then Blue then the alpha/transparency channel on the right. I also added a red box around each one so you can see the extent on StackOverflow's white background.
magick template.png -separate -scale 100x +append channels.png
Keywords: ImageMagick, absolute basics, tutorial, transparency, compose, overlay, command line, image processing.
this sounds like indexed colors / palette effect from the VGA days (like plasma, water and fire) Where you change the palette (in a specific way) and image changes with it.
The idea is that Your image/sprite does not contain RGB colors directly but color indexes from palette instead. Where part of the palette for your image/sprite contains a color gradient so gradients on image are also gradients on index (neighboring shades have also neighboring indexes). Many old pixelart sprites and images from the old days are done this way (sorted palette).
Now you can simply chose few colors in that part of palette and interpolate the rest of the gradient (linearly or better).
To mimic this your need:
have a indexed color pixel art with sorted palette
For example You can convert your image into BMP or GIF with palette and sort the colors.
detect the part of palette with color gradient
change/update the gradient
re-render or recolor image.
I have an image that is essentially a text document (black and white) but due to anti-aliasing/undersampling applied during scanning, the image contains a lot of color, light tone pixels and is thus saved as a full-color image i.e: takes a lot of space.
My goal is to be able to detect Black and White image candidates in order to convert them from full color to B&W which dramatically reduces their size.
Is there a way to detect such anti-aliased/undersampled images? Doing color pixel analysis doesn't help because the colored pixels end up being close in amount to the black pixels... Essentially I want to be able to detect that the colored pixels come from anti-aliasing/undersampling a black & white image and not from a picture type image.
Here is an example image:
As you can see there are many more colors than just black. However this image is a good candidate for Black & White / Greyscale conversion instead of full color. How can I detect such images? Please note that in this example the colors tend to be on the grey side but there are many cases where they are cyan or brown etc.
I think it is a valid question. I don't have 50 reputation to post a comment so I will post this as an answer.
Basically, in a black and white anti-aliased image the various grey colors are opacity differences of the black color. If we observe those pixels they will be like these listed below. So, if the operation is a color manipulation then apply the same opacity picked up from those grey pixels to the new color.
rgba(0,0,0,0.6)
rgba(0,0,0,0.9)
rgba(0,0,0,0.5)
rgba(0,0,0,0.9)
rgba(0,0,0,0.6)
rgba(0,0,0,0.1)
rgba(0,0,0,0.5)
In my opinion, the pixels other than grey, in this example image, cyan and brown as it appears can be safely ignored because they seemed like not part of the original text. If there were a few more example images of non grey pixels would have been good. But if we cannot ignore them just need to get the pixel opacity and apply the same color manipulation. In other words we treat them as black pixels.
I have an array of Colors that represents a picture. I want to find the most bold / most standout color from that frame (aka a bright pink if there is no pink in the frame or a bright yellow if there is no yellow in the frame, etc). Currently I don't know how to do this efficiently. Is there any known or efficient way of doing this efficiently for a 1280 by 720 pixel image (921,600 pixels) or any method you can think of?
As a starting point, I would say you are looking for the most saturated colour, so I would suggest converting to HSL colorspace, discarding the Hue and Lightness and seeing which one has the highest saturation.
So, for a quick example using ImageMagick using these two images:
This is the command yo would run in Terminal:
convert lighthouse.png -colorspace hsl -separate -delete 0,2 saturation.png
And here are the results - the most saturated colours show up as white.
What is meant by red,green or blue plane of a color image?How do we generate the red plane?how is it different from the other planes?Please explain the logic behind generating these planes?
Every pixel in a normal colour image is made up of a red part, a green part and a blue part - hence RGB image. Typically there is one byte for the red part at each location in the image, one for green and one for blue. As there is a byte for each pixel location, the red can vary between 0 (zero) which means "no red" and 255 which means "full red". Likewise the green and blue. So an image where all the pixels are
Red=255, Green=0, Blue=0 will look very bright red
Red=0, Green=255, Blue=0 will look very green
and a pixel where R=G=B will look grey, and if R=G=B=16 it will be very dark grey, and if R=G=B=240 it will be very light/bright grey.
So, the "red plane" is merely an image that only shows the red part of each pixel, or how much red there is in each pixel.
Here is a rose:
and here is the red plane, and you can see that where the rose is very red, the red plane is very bright meaning there is lots of red.:
Here is the green plane (you can see the green leaf on the right is bright):
and the blue plane (you can see the blueish petals on the left are bright):
If you want to separate the color channels (planes), it is very easy in ImageMagick to get the red plane, for example:
convert rose: -channel red -separate red.jpg
ImageMagick is free and amazing - available here.
Simple answer:
Say you read a 480x640 color image, like so:
A = imread('image.jpg');
The matrix A has dimensions 480 x 640 x 3. The third dimension are three 480 x 640 planes, or color channels:
red = A(:,:,1)
green = A(:,:,2)
blue = A(:,:,3)
Now you can go to the link #Trilarion gave in the comments and look at the portion about Truecolor Images.
If I understand your comment, you want to know how a CCD of a camera catch the chroma of each color.
Have a look to color space
And maybe about wavelength of colors (Look at the table of color frequency/wavelength for more informations)
And camera CDD to understand how camera catch those wavelenght and create color channel of an image.