Recently I have tried the phase-shifting-profilometry method to get a 3D surface.
Input Images
Object's Phase Function
Everything went smoothly until I found out that it becomes a Diagonal plane/ Diagonal surface when visualizing the surface due to the unwrapped phase algorithm.
3D object Visualize
I want to ask whether there is any method to make the surface horizontal (like the XY plane).
Sorry that I can not post images here because "I need at least 10 reputation to post images", so Images will be on the link below.
1: https://i.stack.imgur.com/R8BMt.gif
2: https://i.stack.imgur.com/QueKS.png
3: https://i.stack.imgur.com/6jysU.png
Thank you very much!
Ju Lee,
what you are actually plotting is the phase map which can be used to calculate the 3D object. The easiest way (which is only an approximation) to get a depth map is to calculate the phase difference to the phase map of a reference plane (without an object on it):
depth(x,y) ~ a*(phase_map(x,y) - phase_map_reference(x,y)),
where a is a scaling factor you have to determine experimentally. This "easy" procedure is roughly adapted from Takeda's famous 1983 paper: https://doi.org/10.1364/AO.22.003977.
See formula 22 therein for small phase differences.
A more accurate procedure giving the full 3D pointcloud directly from the phase can be found in Zhang's 2006 paper https://doi.org/10.1364/OE.14.009120.
But therefore, you have to calibrate the camera-projector system and calculate an "absolute" phase_map. This typically needs a lot of work, but references therefore are linked in Zhang's paper.
Have fun!
I am training a one-class (hands) object detector on the egohands data set. My problem is that it detects way too many things as hands. It feels like it is detecting everything that is skin-colored as a hand.
I assume the most likely explanation for this is that my training set is poor, as every single image of the set contains hands, and also almost no other skin-toned elements are on the images. I guess it is necessary to also present the network images that are not what you try to detect?
I just want to verify I am right with my assumptions, before investing lots of time into creating a better training set. Therefore I am very grateful for every hint want I am doing wrong.
Object detection preprocessing is critical step, take extra caution guards as detection networks are sensitive to geometrical transformations.
Some proven data augmentation methods include:
1.Random geometry transformation for random cropping (with constraints),
2.Random expansion,
3.Random horizontal flip
4.Random resize (with random interpolation).
5.Random color jittering for brightness, hue, saturation, and contrast
I have a bunch of poor quality photos that I extracted from a pdf. Somebody I know has the good quality photo's somewhere on her computer(Mac), but it's my understanding that it will be difficult to find them.
I would like to
loop through each poor quality photo
perform a reverse image search using each poor quality photo as the query image and using this persons computer as the database to search for the higher quality images
and create a copy of each high quality image in one destination folder.
Example pseudocode
for each image in poorQualityImages:
search ./macComputer for a higherQualityImage of image
copy higherQualityImage to ./higherQualityImages
I need to perform this action once.
I am looking for a tool, github repo or library which can perform this functionality more so than a deep understanding of content based image retrieval.
There's a post on reddit where someone was trying to do something similar
imgdupes is a program which seems like it almost achieves this, but I do not want to delete the duplicates, I want to copy the highest quality duplicate to a destination folder
Update
Emailed my previous image processing prof and he sent me this
Off the top of my head, nothing out of the box.
No guaranteed solution here, but you can narrow the search space.
You’d need a little program that outputs the MSE or SSIM similarity
index between two images, and then write another program or shell
script that scans the hard drive and computes the MSE between each
image on the hard drive and each query image, then check the images
with the top X percent similarity score.
Something like that. Still not maybe guaranteed to find everything
you want. And if the low quality images are of different pixel
dimensions than the high quality images, you’d have to do some image
scaling to get the similarity index. If the poor quality images have
different aspect ratios, that’s even worse.
So I think it’s not hard but not trivial either. The degree of
difficulty is partly dependent on the nature of the corruption in the
low quality images.
UPDATE
Github project I wrote which achieves what I want
What you are looking for is called image hashing
. In this answer you will find a basic explanation of the concept, as well as a go-to github repo for plug-and-play application.
Basic concept of Hashing
From the repo page: "We have developed a new image hash based on the Marr wavelet that computes a perceptual hash based on edge information with particular emphasis on corners. It has been shown that the human visual system makes special use of certain retinal cells to distinguish corner-like stimuli. It is the belief that this corner information can be used to distinguish digital images that motivates this approach. Basically, the edge information attained from the wavelet is compressed into a fixed length hash of 72 bytes. Binary quantization allows for relatively fast hamming distance computation between hashes. The following scatter plot shows the results on our standard corpus of images. The first plot shows the distances between each image and its attacked counterpart (e.g. the intra distances). The second plot shows the inter distances between altogether different images. While the hash is not designed to handle rotated images, notice how slight rotations still generally fall within a threshold range and thus can usually be matched as identical. However, the real advantage of this hash is for use with our mvp tree indexing structure. Since it is more descriptive than the dct hash (being 72 bytes in length vs. 8 bytes for the dct hash), there are much fewer false matches retrieved for image queries.
"
Another blogpost for an in-depth read, with an application example.
Available Code and Usage
A github repo can be found here. There are obviously more to be found.
After importing the package you can use it to generate and compare hashes:
>>> from PIL import Image
>>> import imagehash
>>> hash = imagehash.average_hash(Image.open('test.png'))
>>> print(hash)
d879f8f89b1bbf
>>> otherhash = imagehash.average_hash(Image.open('other.bmp'))
>>> print(otherhash)
ffff3720200ffff
>>> print(hash == otherhash)
False
>>> print(hash - otherhash)
36
The demo script find_similar_images also on the mentioned github, illustrates how to find similar images in a directory.
Premise
I'll focus my answer on the image processing part, as I believe implementation details e.g. traversing a file system is not the core of your problem. Also, all that follows is just my humble opinion, I am sure that there are better ways to retrieve your image of which I am not aware. Anyway, I agree with what your prof said and I'll follow the same line of thought, so I'll share some ideas on possible similarity indexes you might use.
Answer
MSE and SSIM - This is a possible solution, as suggested by your prof. As I assume the low quality images also have a different resolution than the good ones, remember to downsample the good ones (and not upsample the bad ones).
Image subtraction (1-norm distance) - Subtract two images -> if they are equal you'll get a black image. If they are slightly different, the non-black pixels (or the sum of the pixel intensity) can be used as a similarity index. This is actually the 1-norm distance.
Histogram distance - You can refer to this paper: https://www.cse.huji.ac.il/~werman/Papers/ECCV2010.pdf. Comparing two images' histograms might be potentially robust for your task. Check out this question too: Comparing two histograms
Embedding learning - As I see you included tensorflow, keras or pytorch as tags, let's consider deep learning. This paper came to my
mind: https://arxiv.org/pdf/1503.03832.pdf The idea is to learn a
mapping from the image space to a Euclidian space - i.e. compute an
embedding of the image. In the embedding hyperspace, images are
points. This paper learns an embedding function by minimizing the
triplet loss. The triplet loss is meant to maximize the distance
between images of different classes and minimize the distance between
images of the same class. You could train the same model on a Dataset
like ImageNet. You could augment the dataset with by lowering the
quality of the images, in order to make the model "invariant" to
difference in image quality (e.g. down-sampling followed by
up-sampling, image compression, adding noise, etc.). Once you can
compute embedding, you could compute the Euclidian distance (as a
substitute of the MSE). This might work better than using MSE/SSIM as a similarity indexes. Repo of FaceNet: https://github.com/timesler/facenet-pytorch. Another general purpose approach (not related to faces) which might help you: https://github.com/zegami/image-similarity-clustering.
Siamese networks for predicting similarity score - I am referring to this paper on face verification: http://bmvc2018.org/contents/papers/0410.pdf. The siamese network takes two images as input and outputs a value in the [0, 1]. We can interpret the output as the probability that the two images belong to the same class. You can train a model of this kind to predict 1 for image pairs of the following kind: (good quality image, artificially degraded image). To degrade the image, again, you can combine e.g. down-sampling followed by
up-sampling, image compression, adding noise, etc. Let the model predict 0 for image pairs of different classes (e.g. different images). The output of the network can e used as a similarity index.
Remark 1
These different approaches can also be combined. They all provide you with similarity indexes, so you can very easily average the outcomes.
Remark 2
If you only need to do it once, the effort you need to put in implementing and training deep models might be not justified. I would not suggest it. Still, you can consider it if you can't find any other solution and that Mac is REALLY FULL of images and a manual search is not possible.
If you look at the documentation of imgdupes you will see there is the following option:
--dry-run
dry run (do not delete any files)
So if you run imgdupes with --dry-run you will get a listing of all the duplicate images but it will not actually delete anything. You should be able to process that output to move the images around as you need.
Try similar image finder I have developed to address this problem.
There is an explanation and the algorithm there, so you can implement your own version if needed.
I am currently developing hair strand system for my project. Currently I am using verlet integration to simulate gravity and wind.
Wind vector is currently just a vector. But I want to make a more realistic wind.
Is there any papers or articles that I should read about? Thanks.
It depends on how deep you want to go with the simulation. I suppose that you want something more interesting than uniform wind with varying direction and intensity.
I would suggest adding turbulent velocity to each strand with 3D Curl/Simplex noise. Even animated Perlin noise might be cheap and fast enough for your needs, but you might be able to get more dramatic effects with curl noise.
The original paper for curl noise is here: http://www.cs.ubc.ca/~rbridson/docs/bridson-siggraph2007-curlnoise.pdf
You can also find several implementations of it, but the basic idea is still the same - perturbing particles according to an underlying flow-field.
I need to be able to detect a variety of coloured post-it notes via a Microsoft Kinect video stream. I have tried using Emgucv for edge detection but it doesn't seem to locate the vertices/edges and also colour segmentation/detection however considering the variety of colours that may not be robust enough.
I am attempting to use HAAR classification. Can anyone suggest the best variety of positive/negative images to use. For example, for the positive images should I take pictures of many different coloured post-it notes in various lighting conditions and orientations? Seeing as it is quite a simple shape ( a square) is using HAAR classification over-complicating things?
I haar classifiers are typically used on black and white images and trigger primarily on morphologic edge like feature. Seems like if you want to find post it notes in an image the easiest method would be to look at colors (since they come in very distinct colors). Have you tried training a SVM of Random forest classifier to detect post it notes based on just color? Once you've identified areas in the image that are probably post it notes you could start looking at things like the shape as additional validation that you are indeed looking at a post it note.
Take a look at the following as an example of how to find rectangles in an image using hough transform:
https://opencv-code.com/tutorials/automatic-perspective-correction-for-quadrilateral-objects/