How to design convolution kernals?
显示 更早的评论
Design convolution kernels
i. Translating image
ii. Invert the image
iii. Rectify the image
iv. Subtract from each pixel the value of the mean of the contiguous surrounding pixels.
v. Highlight vertical edges by taking a derivative in the horizontal direction only.
vi. Embossing effect below and to the right of image features.
vii. Flip the image left to right.
viii. Make a single kernel to cascade operations i) and ii) above.
Invent and implement and algorithm to determine the amount and direction of shift between the images in ct.jpg and ctshift.jpg.
Please provide a listing of your code, and the shift in both i and j.
6 个评论
Bjorn Gustavsson
2022-10-13
This is one example of how I make a QD low-pass filtering kernel:
fK1 = [.25 .75 1 .75 .25];
fK = conv2(fK/3,fK'/3,'full');
That should illustrate that step in your homework.
HTH
Jiby
2022-10-13
Bjorn Gustavsson
2022-10-14
Sure use that convolution-kernel on your homework assignment image and see what it produces. Then modify it somewhat and see what a convolution with that modified kernel leads to. Then read the textbook and lecture notes, think and ponder.
To increase your chances to get detailed code solving your homework tast you should heed the advice by Steven Lords comment here.
DGM
2022-10-14
Look up a Prewitt or Roberts filter, figure out why it does what it does. Can it be used to answer one of these?
What does fk = [0 0 0 0 1] do?
Consider fk = [0 0 0; 0 1 0; 0 0 0] - [1 1 1; 1 0 1; 1 1 1]/8. Which case does that satisfy? Do you see why?
Remember that convolution is associative; that should provide a means to answer #8.
Note that image()/imagesc()/imshow() will truncate values if they're outside the expected display range, so don't let that confuse you.
Jiby
2022-10-15
Jiby
2022-10-15
采纳的回答
Image Analyst
2022-10-15
0 个投票
Not sure what invert and rectify means. Does it mean spatially or in intensity?
For translate just have a 1-@ or 2-D kernel of a delta function, in other words an array that is all zeros except there is a 1 NOT at the very center of the array but offset some distance from it. The distance away from the center specifies the translation and the direction determines the direction of the shift.
For iv, you can get the mean of all pixels in a 3x3 window with ones(3)/9. To get the mean of the surrounding pixels it would be 1's just in the 8 pixels in the ring (don't include the center) but then you have to divide by 8 instead of 9. So the kernel to subtract that from 1 would be a 3x3 window with 1 in the middle minus that kernel with 1/8's in it.
4 个评论
Jiby
2022-10-15
DGM
2022-10-15
If I recall from a prior version of this question, "rectification" implies the absolute value of the image.
For my own interpretation, "invert" is synonymous with "complement"
outpict = whitevalue - inpict;
however, I have a feeling that the assignment simply means
outpict = -inpict;
I really don't know.
Image Analyst
2022-10-15
I don't know how to either
- invert the intensity of pixels, or
- invert/flip the image right-to-left, or top-to-bottom
using just convolution alone. Of course you can flip the image spatially using fliplr or flipud, and you can invert the intensity just by subtracting the image from a constant, such as the white value of 255 for a uint8 image or 65535 for a 16 bit image.
Normally for some kernel, in general, the output value will be a floating point number (unless all the kernel numbers were integers). So, for whatever reason conv2 won't cast unsigned integer image variables into double -- you have to do that yourself while or before calling conv2. With imfilter it probably does that for you internally. Then, imfilter casts it back to the original unsigned integer class upon returning the result to you. Also, imfilter does not flip the kernel like convolution does, so it's more like a correlation than a convolution because of that. But correlation and convolution are the same except that convolution flips the kernel. There are theoretical, mathematical reasons for that. Also, imfilter has a lot more choices for how to handle the edge situation, like when the sliding window is in a location where part of the window is "off the image".
Jiby
2022-10-15
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Image Processing Toolbox 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
