Author Topic: Pixel Confusion....  (Read 1913 times)

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Offline KAP

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Pixel Confusion....
« on: March 05, 2011, 12:34:55 AM »
Now right off the bat I will warn that I'm sure this is a stupid question but it's bothering me so I thought I would ask...

Usually, my photos right out of the camera end up with a pixel dimension something like:  Width - 4592 / Height - 3056

When I began entering photos in competitions at the camera club I joined the rules were a pixel width of 1024.   Now, I began to notice that reducing to a pixel width of 1024 ended up in a sharper photo... my photo would be ready to go and good and then I would do the 1024 resizing in PSE and.. sharper photo - not by a lot but just a touch sharper and visible to my eye.  It seemed to bring in more detail.  My resolution does not change - it's 72.

Why is this? 
Gear:  Sony Alpha 350, 77 with a variety of Minolta and Sony lenses.

Offline Stef.

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Re: Pixel Confusion....
« Reply #1 on: March 06, 2011, 07:56:42 PM »
72 dpi is the normal screen resolution. Any higher resolution than 72 is hard to see on a monitor. When you want to print something then you will have to un-tick "resample" and put 300 instead of 72 in that box. You will see that then the dimensions of width and length will change accordingly.

Why do smaller images look sharper? That's something that has been around for ever. If you look at 6 by four inch prints they always look sharper than the same image at bigger sizes. Therefore the sharpening in any software should always be done after re-sizing or re-sampling the shot to the outputsize. Smaller images need less sharpening than bigger one.

On a general note: I have used the word re-sizing and re-sampling: I am not sure wheether you knwo the difference:
The better is always re-sizing (!) Here you have to untick the word "resample" and when you change the width or height of your image the resolution will NOT (!) stay at 72 but it will change! The same the other way around: if you change rthe resolution from 72 to 300 for printing then the output size WILL change. What you are effectively doing is to distribute all the pixels to a different size without adding or taking away any pixels.

Re-sampling is a whole different ball game and a can of worms...what you are effectively doing here is inventing new pixels or throwing some out. You are asking the computer program to look at the nearest pixels and to decide what colour pixel it should add. In effect you 72 will stay the same but if you are downsampling to a smaller size the computer will just throw out pixels...this can lead to sometimes sharper "looking" images or when you up-sample to softer images. Re-sampling should be avoided whenever possible- which for weboutput is tricky.

The difference between re-sizing and re-sampling has led unfortunately to a lot of confusion in the past...

Hope this clarifies it a bit?
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