dct and idct are the same formula? about image-transform-dct-and-idct HOT 7 CLOSED

denpo1022 commented on September 4, 2024

dct and idct are the same formula?

from image-transform-dct-and-idct.

Comments (7)

denpo1022 commented on September 4, 2024

Hi @yuan243212790 , actually they are not the same formula.

Here the DCT formula:

and the IDCT one:

If you replace C(i), C(j) above with C(u), C(v) then you can understand the code more easily.

from image-transform-dct-and-idct.

yuan243212790 commented on September 4, 2024

can you tell me what the differences?just exchange f(X,Y) and D(X,Y)

from image-transform-dct-and-idct.

denpo1022 commented on September 4, 2024

@yuan243212790 Maybe explain with the code will be better:

One of the differences you should watch out is the position where calculating C(i) C(j) ( Cu Cv in the code).
For DCT, calculate C(i) C(j) right after the first nested for loop (means before double Σ in the formula).

Image-Transform-DCT-and-IDCT/main.py

Lines 17 to 28 in 31f20bd

 for u in range(M): 

 for v in range(N): 

 # according from the formula of DCT 

 if u == 0: 

 Cu = 1 / np.sqrt(M) 

 else: 

 Cu = np.sqrt(2) / np.sqrt(M) 

 if v == 0: 

 Cv = 1 / np.sqrt(N) 

 else: 

 Cv = np.sqrt(2) / np.sqrt(N)

For IDCT, the calculation is located after second nested for loop (means after double Σ in the formula).

Image-Transform-DCT-and-IDCT/main.py

Lines 51 to 67 in 31f20bd

 for x in range(M): 

 for y in range(N): 

 # calculate IDCT 

 tmp_sum = 0 

 for u in range(M): 

 for v in range(N): 

 # according from the formula of IDCT 

 if u == 0: 

 Cu = 1 / np.sqrt(M) 

 else: 

 Cu = np.sqrt(2) / np.sqrt(M) 

 if v == 0: 

 Cv = 1 / np.sqrt(N) 

 else: 

 Cv = np.sqrt(2) / np.sqrt(N)

Also be careful with the variables name I used in the nested for loop.
(In DCT outer nested for loop uses u and v, inner one uses x and y. In IDCT outer nested for loop uses x and y, inner one uses u and v)

from image-transform-dct-and-idct.

yuan243212790 commented on September 4, 2024

I know what you mean, but I mean that these ci cj are constants, and the calculation method is essentially the same，just exchange F and f

…

------------------ 原始邮件 ------------------ 发件人: ***@***.***>; 发送时间: 2022年7月6日(星期三) 下午5:06 收件人: ***@***.***>; 抄送: ***@***.***>; ***@***.***>; 主题: Re: [denpo1022/Image-Transform-DCT-and-IDCT] dct and idct are the same formula? (Issue #1) @yuan243212790 Maybe explain with the code will be better: One of the differences you should watch out is the position where calculating C(i) C(j) ( Cu Cv in the code). For DCT, calculate C(i) C(j) right after the first nested for loop (means before double Σ in the formula). https://github.com/denpo1022/Image-Transform-DCT-and-IDCT/blob/31f20bdd03a61cf03e11bb4f388a615093d6c34c/main.py#L17-L28 For IDCT, the calculation is located after second nested for loop (means after double Σ in the formula). https://github.com/denpo1022/Image-Transform-DCT-and-IDCT/blob/31f20bdd03a61cf03e11bb4f388a615093d6c34c/main.py#L51-L67 Also be careful with the variables name I used in the nested for loop. (In DCT outer nested for loop uses u and v, inner one uses x and y. In IDCT outer nested for loop uses x and y, inner one uses u and v) — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

from image-transform-dct-and-idct.

denpo1022 commented on September 4, 2024

I won't call them exactly the same but yes the basic idea and concept of the both formulas are pretty similar.
For me it's more clear to treat DCT and IDCT as distinct formulas, but now I understand your opinion and the way of thinking.
Regarding DCT and IDCT as the same would be fine, just be careful when implementing with the code :D

from image-transform-dct-and-idct.

yuan243212790 commented on September 4, 2024

Thank you very much！I just want to know the implement in code are the same，Only one is the operation of the original image, and the other is the post-processing of the former

…

------------------ 原始邮件 ------------------ 发件人: ***@***.***>; 发送时间: 2022年7月6日(星期三) 晚上6:41 收件人: ***@***.***>; 抄送: ***@***.***>; ***@***.***>; 主题: Re: [denpo1022/Image-Transform-DCT-and-IDCT] dct and idct are the same formula? (Issue #1) I won't call them exactly the same but yes the basic idea and concept of the both formulas are pretty similar. For me it's more clear to treat DCT and IDCT as distinct formulas, but now I understand your opinion and the way of thinking. Regarding DCT and IDCT as the same would be fine, just be careful when implementing with the code :D — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>

from image-transform-dct-and-idct.

denpo1022 commented on September 4, 2024

Thank you very much！I just want to know the implement in code are the same，Only one is the operation of the original image, and the other is the post-processing of the former
…
------------------ 原始邮件 ------------------ 发件人: @.>; 发送时间: 2022年7月6日(星期三) 晚上6:41 收件人: @.>; 抄送: @.>; @.>; 主题: Re: [denpo1022/Image-Transform-DCT-and-IDCT] dct and idct are the same formula? (Issue #1) I won't call them exactly the same but yes the basic idea and concept of the both formulas are pretty similar. For me it's more clear to treat DCT and IDCT as distinct formulas, but now I understand your opinion and the way of thinking. Regarding DCT and IDCT as the same would be fine, just be careful when implementing with the code :D — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: @.***>

No problem. You can always launch a new issue whenever you got something want to ask.

from image-transform-dct-and-idct.

dct and idct are the same formula? about image-transform-dct-and-idct HOT 7 CLOSED

Comments (7)

Related Issues (1)

Recommend Projects

React

Vue.js

Typescript

TensorFlow

Django

Laravel

D3

Recommend Topics

javascript

web

server

Machine learning

Visualization

Game

Recommend Org

Facebook

Microsoft

Google

Alibaba

D3

Tencent

	for u in range(M):
	for v in range(N):

	# according from the formula of DCT
	if u == 0:
	Cu = 1 / np.sqrt(M)
	else:
	Cu = np.sqrt(2) / np.sqrt(M)
	if v == 0:
	Cv = 1 / np.sqrt(N)
	else:
	Cv = np.sqrt(2) / np.sqrt(N)

	for x in range(M):
	for y in range(N):

	# calculate IDCT
	tmp_sum = 0
	for u in range(M):
	for v in range(N):

	# according from the formula of IDCT
	if u == 0:
	Cu = 1 / np.sqrt(M)
	else:
	Cu = np.sqrt(2) / np.sqrt(M)
	if v == 0:
	Cv = 1 / np.sqrt(N)
	else:
	Cv = np.sqrt(2) / np.sqrt(N)