Is hi-res + shrink better than taking lo-res?

If i take pictures in hi-resolution 1600X1200 and then shrink to
800X600 is it better quality to just take picture in 800X600 mode?

It depends on how much you lose in JPEG compression. If you compress
the 1600x1200 image, then uncompress it, scale it, and recompress it,
you'll probably end up worse than if you'd just shot at 800x600. If
you use your camera's "fine" JPEG setting, though, you probably won't
lose much, and you may gain a lot of you decide you want to crop the
1600x1200 image instaed of shrinking it.

-Joel

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On a similar note, is it better to use digital zoom or to
just crop later? or is this just chicken or the egg?

I'd never want to use Digital Zoom for anything. I'd take the
pic and save the original and crop later and then saveas that
cropped file to a different name.

I've also never used the digital zoom, but, again, depending on JPEG
compression, the digital zoom may give you better results than
cropping after a round of compression and uncompression.

-Joel

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Dr. Joel M. Hoffman wrote:
On a similar note, is it better to use digital zoom or to
just crop later? or is this just chicken or the egg?
I'd never want to use Digital Zoom for anything. I'd take the
pic and save the original and crop later and then saveas that
cropped file to a different name.

I've also never used the digital zoom, but, again, depending on JPEG
compression, the digital zoom may give you better results than
cropping after a round of compression and uncompression.

This pretty much flies in the face of at least conventional wisdom. On
what basis to you speculate??

--
John McWilliams

Dr. Joel M. Hoffman wrote:
If i take pictures in hi-resolution 1600X1200 and then shrink to
800X600 is it better quality to just take picture in 800X600 mode?

It depends on how much you lose in JPEG compression. If you compress
the 1600x1200 image, then uncompress it, scale it, and recompress it,
you'll probably end up worse than if you'd just shot at 800x600.

Yes, but as the Dr. says, "Don't do that."
If
you use your camera's "fine" JPEG setting, though, you probably won't
lose much, and you may gain a lot of you decide you want to crop the
1600x1200 image instaed of shrinking it.

Even if one is merely downsizing the resolution and/or number of pixels,
one is best off starting with the highest resolution the camera is
capable of.

Joel- in my question of you upthread, there's a typo....

--
John McWilliams

I've also never used the digital zoom, but, again, depending on JPEG
compression, the digital zoom may give you better results than
cropping after a round of compression and uncompression.

This pretty much flies in the face of at least conventional wisdom. On
what basis to you speculate??

If you are going to crop the image anyway, so that, either way, you'll
only be using --- let's say --- the middle 50% of the sensor, then you
have two choices:

1. Take the information from the entire sensor, JPEG encode it, JPEG
decode it, take the middle 50%, and then re-encode it. There's no
way you can avoid getting some noise from the outer part of the
image (which you aren't even using) and there's no way you can
avoid the degredation from the JPEG encode decode.

2. Take the information from the middle 50% of the sensor, and JPEG
encode you. You don't get noise from the part of the image you
don't need, and you don't suffer an encode/decode cycle.

Now, it may be that the noise from the outside of the image is
negligible, and it may be that the degradation from the encode/decode
cycle is minimal, and it also may be that a good computer program
can do a better job upsizing the image than the camera's software can,
but these various assumptions are not obvious, nor, do I believe,
always true.

To take a concret example, if you take a picture of a deer, and the
deer only occupies half of the frame, and you want to a make a 6x8
printed photo of just the deer, you only have 800x600 of image data,
or 100dpi. If your printer prints at 150 dpi, you need to fill in the
missing dots. I don't know if the improvements you can make with
advanced computer software outweigh the disadvantage of encoding and
decoding the image an extra time. I also don't know if the camera can
optimize the upsampling by working with the raw un-JPEG'd data.

-Joel



Joel M. Hoffman, PhD
http://www.lashon.net/JMH

John McWilliams wrote:
Dr. Joel M. Hoffman wrote:
On a similar note, is it better to use digital zoom or to
just crop later? or is this just chicken or the egg?
I'd never want to use Digital Zoom for anything. I'd take the
pic and save the original and crop later and then saveas that
cropped file to a different name.

I've also never used the digital zoom, but, again, depending on JPEG
compression, the digital zoom may give you better results than
cropping after a round of compression and uncompression.

This pretty much flies in the face of at least conventional wisdom. On
what basis to you speculate??

I tested this (but some time ago) and found that 2:1 digital zoom was
indeed better than cropping after compression. The larger image in the
viewfinder may also help composition or focussing.

I would suggest testing on your own camera, though.

David