Viewing digital photos on screen - regarding resolution

[KamWeng]

Hi all,

May be I'm wrong, but I found that when viewing digital photos on screen, the optimum results (sharp display) were from photos with resolution of 4x screen resolution, or 2x the dimensions (W & H). That is: 1600x1200 (2MP) is best viewed with 800x600 screen, 2048x1536 (3MP) is best viewed with 1024x768 screen.

Very high resolution photos when viewed with very low resolution screen would have details lost due to dithering. The other way round would have a soft display.

Is this true, or it's just me?

 

[hwchoy]

are you using an LCD screen?

 

[linse]

I find that it makes no noticable difference whether the resolution of the photo is in multiples of whole numbers. Once you go above a certain resolution, the photo does not get any sharper. However, the higher the original resolution, the lower the noise as the pixels average out.

I think your findings are related the the image viewer you are using. Sounds like it is not using a very good algorythm and hence can't resize well unless the resize ratio is in whole numbers.

 

[hwchoy]

LCD screens have difficulties with odd ratio scaling due to fixed pixel elements vs CRT which is analog in nature (the electron beam).

 

[KamWeng]

Yes, I'm using an LCD screen.

For example when we diaplay a photo on screen, then we press the "-" repeatedly to reduce the photo's display size. Up to certain extent the display will start to lose details due to dithering. Isn't it the same thing?

 

[KamWeng]

LCD screens have difficulties with odd ratio scaling due to fixed pixel elements vs CRT which is analog in nature (the electron beam).

In this case, is it the CRT when displaying 1024x768 still shows more details (pixels) than an LCD which also displaying 1024x768? :think:

 

[Lennier]

That is: 1600x1200 (2MP) is best viewed with 800x600 screen, 2048x1536 (3MP) is best viewed with 1024x768 screen.

Hmm, I'm not sure how screens work, here's my take, see if it makes any sense.

That means you're viewing the image at less than 100% magnification. It might appear sharper because you're looking at a smaller image so the "imperfections" don't seem so apparent (kinda like looking at a slide with a 2x loupe compared to a 20x loupe).

You shouldn't have any problems from dithering unless you've magnified the image beyond 72dpi.

Some other factors will affect sharpness of the display however... dot pitch, ambient lighting, etc.

 

[hwchoy]

basically LCD screens are made up of discrete elements, which is why you never get a satisfactory resolution if you change it from the hardware resolution. e.g. if you have the SXGA screen which has 1400×1050 resolution, and you set display to 800×600, it will still look damn yucky even though the aspect ratios are the same. Because your 800 pixels will not display properly over 1400 physical "pixels".

In the case of CRT it is an analog device, so the 800 pixels will spread out "evenly" over the width of the scanned area. Do note that the phosphor spots on a CRT does not correspond to the physical pixels on an LCD.