# Dct error when using Images
**URL:** https://discourse.julialang.org/t/dct-error-when-using-images/111775
**Category:** New to Julia
**Tags:** float
**Created:** [March 18, 2024, 2:54pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775 "2024-03-18T14:54:00Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@AbdelazimHussien](https://discourse.julialang.org/u/AbdelazimHussien)
#### Post date: [March 18, 2024, 2:54pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/1 "2024-03-18T14:54:00Z")
Hello everyone,
I have the following code
```julia
using TestImages, ImageView
img = testimage("cameraman")
pixels = img[1:8,1:8]
pixels = convert(Array{Float32}, pixels)
freqs = dct(pixels)
round(freqs)
pixels2 = idct(freqs)
```
but i can not find dct function so i got the following error
UndefVarError: dct not defined
Thanks in advanced
---
### Author:  [@sefffal](https://discourse.julialang.org/u/sefffal)
#### Post date: [March 18, 2024, 2:58pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/2 "2024-03-18T14:58:20Z")
Hello,
Try loading the FFTW package: `using FFTW`
[https://juliamath.github.io/FFTW.jl/latest/fft.html](https://juliamath.github.io/FFTW.jl/latest/fft.html)
---
### Author:  [@AbdelazimHussien](https://discourse.julialang.org/u/AbdelazimHussien)
#### Post date: [March 18, 2024, 4:24pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/3 "2024-03-18T16:24:03Z")
Thanks a lot.
It works now. But my question is that pixels == pixels2 should be true but it is false. can U help me with this?
Here is the full code
````img
pixels = img[1:8,1:8]
pixels = convert(Array{Float32}, pixels)
freqs = dct(pixels)
round(freqs)
pixels2 = idct(freqs)
pixels == pixels2```
Thanks
````
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [March 18, 2024, 4:46pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/4 "2024-03-18T16:46:32Z")
> [@AbdelazimHussien](#):
>
> But my question is that pixels == pixels2 should be true but it is false.
Floating-point rounding errors will make them slightly unequal. If you do:
```julia
using LinearAlgebra
norm(pixels - pixels2) / norm(pixels2)
```
you should see that the relative difference is extremely small. More succinctly, you could check `pixels ≈ pixels2`, which calls [`isapprox`](https://docs.julialang.org/en/v1/base/math/#Base.isapprox).
---
### Author:  [@AbdelazimHussien](https://discourse.julialang.org/u/AbdelazimHussien)
#### Post date: [March 18, 2024, 5:03pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/5 "2024-03-18T17:03:46Z")
so how to solve this problem?
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [March 18, 2024, 5:06pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/6 "2024-03-18T17:06:06Z")
You should always expect small rounding errors in any nontrivial floating-point calculation. Why is it a problem for you?
---
### Author:  [@AbdelazimHussien](https://discourse.julialang.org/u/AbdelazimHussien)
#### Post date: [August 18, 2024, 8:40am UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/7 "2024-08-18T08:40:49Z")
I am so sorry
but when I tried it again now. It is not work. I don’t know why even if I write FFTW.dct
Any Suggestions?
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [August 18, 2024, 12:54pm UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/8 "2024-08-18T12:54:01Z")
Broadcast `round()` when applied to the matrix of floats `freqs`, as follows:
`round.(freqs)`
---
### Author:  [@yhuang](https://discourse.julialang.org/u/yhuang)
#### Post date: [August 26, 2024, 2:54am UTC](https://discourse.julialang.org/t/dct-error-when-using-images/111775/9 "2024-08-26T02:54:27Z")
Actually, `pixels` and `pixels2` should not even be close since you applied the `round` step, which brings you some loss.