Does an inadequate pixel-density cause spatial aliasing?

bharat pathak wrote:
> Hi,
> 
>    Let's look at it from sampling theorem perpective. Any
>    ADC has 2 stages.
> 
>    1. first  stage that performs time  discretization.
>    2. second stage that performs value discretization.
> 
>    Time discretization will tell how fine a pixel could be.
>    Basically the resolution of the image like 512x512 pixels
>    or 1920x1080 pixels. One aspect of image looking coarse
>    or fine can come from this. This exactly is something like
>    your digital camera specifying 5 mega pixels or 10 mega
>    pixels. If you are not making hoardings out of your photos
>    then you really don't have to buy 10 mega pixel camera.
>    So this pixel density makes sense only when you tell what
>    size of display in inches u r going to display or print the
>    image and what is the distance from which you will be viewing
>    the same.
> 
>    Second aspect is pixel depth (or value quantization). Let
>    us assume that a gray scale pixel could be represented using
>    8 bit depth. But instead you represented using 4 bit depth
>    then the image is coarsely quantized and thus causes contouring
>    artifacts. The one that u see on you tube fall under this 
>    category. Originally the video would like fine. but due to
>    compression, you see blocking artifacts (which u refer as 
>    pixellation/jagginess). 
> 
> Hope this clears some cloud.
> 
> Bharat Pathak
> 
> Arithos Designs
> www.Arithos.com
> 
> DSP Design Consultancy and Training Company.
> 
> 
> 
> 


http://www.usu.edu/sanderso/multinet/depth.html

"Pixel Depth refers to the number of colors possible on screen."

Sorry to be such a pain but an inadequate pixel-depth does not cause 
'blocking', it causes there to be fewer colors available.

It is an inadequate amount of pixels-per-area that causes blocking.

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Ron N wrote:


> On May 26, 10:13 am, "Green Xenon [Radium]" <gluceg...@excite.com>
> wrote:


>> You say pixelation/jaggies have nothing to do with aliasing. Then why
>> does an insufficient pixelXpixel resolution cause an image to pixelate?


> 
> Pixels can become visible because of the addition of high
> frequency edges during the imaging process.  


Even smooth too-high-frequency sine-wave-like spatial signals can cause 
pixels to become visible as well, right?

The high-frequency signal does not have to have sharp components [i.e. 
waveforms other than sine] to cause 'blocking'.


> Depends on
> whether you are talking about the pixel resolution of the
> capture, the compressed storage format, the decompressed
> image format, or the display format, and/or any conversion
> or filtering processes between any of the above and also
> between the display and the back of the viewers eyeballs.


I am definitely talking about the compressed storage format and 
decompressed image format. Maybe also the capture.

On May 26, 10:41 pm, "Green Xenon [Radium]" <gluceg...@excite.com>
wrote:
> It is an inadequate amount of pixels-per-area that causes blocking.

Inadequate pixel density does not have to cause blocking
unless you display those pixels as adjacent rectangles with
sharp edges of sufficient difference in luminance or color.
If you do, then even a very high pixel-per-area count image
and display might still look "blocky" under a good magnifier.



IMHO. YMMV.