Relation of Frequency and Time with Images ?

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Sufyan
Sufyan 2012-9-2
If we look deeply into Digital Images they are purely generated by the pixels distributed in rows and column and the pixel consists of number of certain bits which define the complete Image.
Then what is the role of Frequency in generating Digital Images ? like many people says that in Digital Image processing and Image Compression, Wavelets is much more efficient than Discrete Cosine Transform as Wavelets gives the information of both time and Frequency.
I want to know what role does frequency and time plays in producing a Digital image, does it has to do something with pixels?

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回答（1 个）

Image Analyst
Image Analyst 2012-9-2
Your question is very vague so I'm not sure how to answer.
High spatial frequencies mean things that change gray level in a shorter distance, like edges and fine details. Low spatial frequencies are things that very slowly, like backgrounds or illumination patterns.
Time is related to exposure. If you collect photons for a longer period of time, the image will be brighter. Shorter exposure time means dimmer images.
Yes it has something to do with pixels -- how much they change from pixel to pixel, and how bright the pixel is.
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Sufyan
Sufyan 2012-9-2
I'm actually more concerned about the frequency and time components as wavelet graph shows both the information, I've slightly understand what you said about frequency but what does the time component tell about an image, like if i have a graphical presentation of any image in a wavelet form , what information that graph would reveal about the image from the time and frequency ? does it tell us the location of the pixel ?
Image Analyst
Image Analyst 2012-9-2
The only time involved with an image is the exposure time. I think you're getting confused with the x and y axes of an image. They're spatial coordinates, not time coordinates. I don't have the wavelet toolbox and I don't know what graphical presentation you're talking about (maybe the LL, LH, HL, and HH quadrants????) but I think the only frequencies wavelets deal with in images are the spatial frequencies. I can't imagine what time oscillations there would be, unless it was something like a video of some scene that was oscillating in intensity.

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