A simple question

wildman · 10-16-2012, 01:53 PM

This doesn't keep me up at nights but just wondering.

Why is the convention, when resizing an image in photography, to define image "size" by dimension rather than area?

In other words when we blow up an image by, say, "200%" we get an image who's dimensions have increased by a factor of 2 but whose area has increased by a factor of 4.

So a 100px x 100px image "enlarged" by 200% could be either 200px x 200 px (dimension)
or
141px x 141px (area).

My guess it's just because dimension is easier to visualize for the average photographer than area.

SpecialK · 10-16-2012, 01:58 PM

Yes, that.

wildman · 10-16-2012, 02:06 PM

Originally posted by SpecialK

Yes, that.

Ever see software that gave you the option of enlarging by area as well as dimension?
I would think it would be simple enough to do on a computer.

SpecialK · 10-16-2012, 02:11 PM

I have never seen that. I do not think people "see" in terms of area, but in length or width which makes more sense as you are frequently using one of those dimensions - such as forum image-width, or picture frame size.

wildman · 10-16-2012, 02:26 PM

Originally posted by SpecialK

I do not think people "see" in terms of area, but in length or width which makes more sense.

It depends I suppose.
I live in a very rural area and when you say "Sam has doubled the "size" of his farm" it's well understood you are talking about area.

But yes, for us photographers, dimension is easier and more meaningful I suppose.

demp10 · 10-16-2012, 04:50 PM

Because we refer to the scale of the photograph. Think of the scale bars on a map.

I suppose it is a lot easier to visualize one dimension at a time.

DSims · 10-16-2012, 06:24 PM

It's the change in the diameter of a pixel, so to speak.

wildman · 10-16-2012, 06:35 PM

Originally posted by DSims

It's the change in the diameter of a pixel, so to speak.

And this is exactly where area has meaning. With a conventional 200% blowup where the original had one pixel now you have 4 which has important implications for the quality of the blowup.

DSims · 10-16-2012, 07:08 PM

Originally posted by wildman

And this is exactly where area has meaning. With a conventional 200% blowup where the original had one pixel now you have 4 which has important implications for the quality of the blowup.

Perhaps this is why some photographers like to go to 300% - they get 3x3 instead of 2x2 for each pixel, which it seems would be better in some ways.

John Poirier · 10-16-2012, 10:34 PM

Originally posted by wildman

This doesn't keep me up at nights but just wondering.

Why is the convention, when resizing an image in photography, to define image "size" by dimension rather than area?

In other words when we blow up an image by, say, "200%" we get an image who's dimensions have increased by a factor of 2 but whose area has increased by a factor of 4.

So a 100px x 100px image "enlarged" by 200% could be either 200px x 200 px (dimension)
or
141px x 141px (area).

My guess it's just because dimension is easier to visualize for the average photographer than area.

Image dimensions in pixels are an indicator of resolution, while physical dimensions are a measurement of ouput size. Both have fairly direct applications. I'd say you're right- it is easier to visualize the effects of changes in dimensions.

Changes in area correlate directly to changes in file size, which is useful information but probably takes third place in terms of frequency of use most of the time. For example, I need to know that an image file 3000 pixels across at 300 pixels per inch will output nicely as a print 10 inches across. The size of the file involved in terms of area/storage requirements is a secondary issue.

panoguy · 10-18-2012, 09:08 AM

Originally posted by wildman

Ever see software that gave you the option of enlarging by area as well as dimension?

Genuine Fractals used to have this option... not sure if (it's replacement) "Perfect Resize" does as well.

wildman · 10-19-2012, 04:00 AM

Originally posted by panoguy

Genuine Fractals used to have this option... not sure if (it's replacement) "Perfect Resize" does as well.

I have the latest version of Perfect Resize and can't find this feature. But I'm not very familiar with it so I could be missing it somehow.

SLThomas · 10-20-2012, 08:13 AM

Originally posted by wildman

It depends I suppose.
I live in a very rural area and when you say "Sam has doubled the "size" of his farm" it's well understood you are talking about area.

But yes, for us photographers, dimension is easier and more meaningful I suppose.

Not to beat a dead horse, but doubling the area can be done in more than one way, and thus is inherently ambiguous. For example, 300x400 px (area of 120000 px) can be doubled as 240000px, but the dimensions could be 400x600px or 300x800px.

We (naturally) assume that the proportions of length and width will remain the same when we "double" the area, but it doesn't have to be the case. But if we double the dimensions, we know the proportions.

wildman · 10-20-2012, 04:38 PM

Originally posted by SLThomas

but doubling the area can be done in more than one way, and thus is inherently ambiguous.

Ambiguous for a human, perhaps, but not for a computer.
If you tell a computer to simply double the area of a given bitmap without further instructions it could do nothing but maintain the original aspect ratio.

10-16-2012, 01:53 PM	#1
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469	A simple question This doesn't keep me up at nights but just wondering. Why is the convention, when resizing an image in photography, to define image "size" by dimension rather than area? In other words when we blow up an image by, say, "200%" we get an image who's dimensions have increased by a factor of 2 but whose area has increased by a factor of 4. So a 100px x 100px image "enlarged" by 200% could be either 200px x 200 px (dimension) or 141px x 141px (area). My guess it's just because dimension is easier to visualize for the average photographer than area.

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10-16-2012, 01:58 PM	#2
SpecialK Pentaxian Join Date: Dec 2006 Location: So California Photos: Gallery Posts: 16,482	Yes, that.

10-16-2012, 02:06 PM	#3
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469 Original Poster	Originally posted by SpecialK Yes, that. Ever see software that gave you the option of enlarging by area as well as dimension? I would think it would be simple enough to do on a computer.

10-16-2012, 02:11 PM	#4
SpecialK Pentaxian Join Date: Dec 2006 Location: So California Photos: Gallery Posts: 16,482	I have never seen that. I do not think people "see" in terms of area, but in length or width which makes more sense as you are frequently using one of those dimensions - such as forum image-width, or picture frame size.

10-16-2012, 02:26 PM	#5
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469 Original Poster	Originally posted by SpecialK I do not think people "see" in terms of area, but in length or width which makes more sense. It depends I suppose. I live in a very rural area and when you say "Sam has doubled the "size" of his farm" it's well understood you are talking about area. But yes, for us photographers, dimension is easier and more meaningful I suppose.

10-16-2012, 04:50 PM	#6
demp10 Veteran Member Join Date: Jun 2011 Location: Atlanta Photos: Albums Posts: 602	Because we refer to the scale of the photograph. Think of the scale bars on a map. I suppose it is a lot easier to visualize one dimension at a time.

10-16-2012, 06:24 PM	#7
DSims Veteran Member Join Date: Sep 2009 Location: Southern California Photos: Gallery \| Albums Posts: 3,236	It's the change in the diameter of a pixel, so to speak.

10-16-2012, 06:35 PM	#8
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469 Original Poster	Originally posted by DSims It's the change in the diameter of a pixel, so to speak. And this is exactly where area has meaning. With a conventional 200% blowup where the original had one pixel now you have 4 which has important implications for the quality of the blowup.

10-16-2012, 07:08 PM	#9
DSims Veteran Member Join Date: Sep 2009 Location: Southern California Photos: Gallery \| Albums Posts: 3,236	Originally posted by wildman And this is exactly where area has meaning. With a conventional 200% blowup where the original had one pixel now you have 4 which has important implications for the quality of the blowup. Perhaps this is why some photographers like to go to 300% - they get 3x3 instead of 2x2 for each pixel, which it seems would be better in some ways.

10-16-2012, 10:34 PM	#10
John Poirier Veteran Member Join Date: Dec 2006 Location: Gabriola Island Posts: 619	Originally posted by wildman This doesn't keep me up at nights but just wondering. Why is the convention, when resizing an image in photography, to define image "size" by dimension rather than area? In other words when we blow up an image by, say, "200%" we get an image who's dimensions have increased by a factor of 2 but whose area has increased by a factor of 4. So a 100px x 100px image "enlarged" by 200% could be either 200px x 200 px (dimension) or 141px x 141px (area). My guess it's just because dimension is easier to visualize for the average photographer than area. Image dimensions in pixels are an indicator of resolution, while physical dimensions are a measurement of ouput size. Both have fairly direct applications. I'd say you're right- it is easier to visualize the effects of changes in dimensions. Changes in area correlate directly to changes in file size, which is useful information but probably takes third place in terms of frequency of use most of the time. For example, I need to know that an image file 3000 pixels across at 300 pixels per inch will output nicely as a print 10 inches across. The size of the file involved in terms of area/storage requirements is a secondary issue.

10-18-2012, 09:08 AM	#11
panoguy Pentaxian Join Date: Sep 2007 Location: Washington, D.C. Photos: Gallery \| Albums Posts: 3,327	Originally posted by wildman Ever see software that gave you the option of enlarging by area as well as dimension? Genuine Fractals used to have this option... not sure if (it's replacement) "Perfect Resize" does as well.

10-19-2012, 04:00 AM	#12
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469 Original Poster	Originally posted by panoguy Genuine Fractals used to have this option... not sure if (it's replacement) "Perfect Resize" does as well. I have the latest version of Perfect Resize and can't find this feature. But I'm not very familiar with it so I could be missing it somehow.

10-20-2012, 08:13 AM	#13
SLThomas New Member Join Date: Oct 2012 Location: Virginia Photos: Albums Posts: 24	Originally posted by wildman It depends I suppose. I live in a very rural area and when you say "Sam has doubled the "size" of his farm" it's well understood you are talking about area. But yes, for us photographers, dimension is easier and more meaningful I suppose. Not to beat a dead horse, but doubling the area can be done in more than one way, and thus is inherently ambiguous. For example, 300x400 px (area of 120000 px) can be doubled as 240000px, but the dimensions could be 400x600px or 300x800px. We (naturally) assume that the proportions of length and width will remain the same when we "double" the area, but it doesn't have to be the case. But if we double the dimensions, we know the proportions.

10-20-2012, 04:38 PM	#14
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469 Original Poster	Originally posted by SLThomas but doubling the area can be done in more than one way, and thus is inherently ambiguous. Ambiguous for a human, perhaps, but not for a computer. If you tell a computer to simply double the area of a given bitmap without further instructions it could do nothing but maintain the original aspect ratio.