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Mega Pixels - Dots per inch


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Not wishing to ruffle any feathers, but the original post 'Fuji cameras' by Janet took a direction re the above . . .

 

Mulled it over in my mind since then, not to sure of true understanding whats going on??

 

So, as I new that my cameras were set at 'X' dots per inch . . . first where did I get this information . . . it finally came to me, when I re-size a picture, the drop down menu, gives, in the case of my Canon S50 compact, 180 pixels per inch, in the case of the Nikon D80 its 300ppi. I vaguely remember these figures used to be talked of in reviews, cant recall this in recent times?

 

So, I took four pictures at four different mega pixel ratings with my S50, L=2592x1944mp, M1=1600x1200mp, M2=1024x768mp and S=640x480mp. Transferred these to Elements v.7, and put them up for re-size. In all cases they came up at 180ppi . . . ? very confusing but more thought. I then clicked on the show on screen at print size . . . did not note the actual A"xB", but all came on screen at an appropriate size to the 'mega pixel' designation, ie, large, smaller, even smaller and a stamp!!! :lol:

 

Confirming, in my mind, the 'megapixel thing' is a sales gimmick, the 'X' millions of mega pixels you get gives a bigger picture, but the 'detail information' that is governed by pixels per inch is constant, as preset by the camera/sensor/processing. This can be changed at 'post processing', but cannot exceed the upper limit on ppi dictated by the sensor, at present this figure seems to be a maximum for DSLR's 300ppi, without interpolation? and upto 180ppi on compacts, not sure wher the pro., full size sensor sits?

 

As I say I'm not into arguments here, just trying to understand what is actually going on, and suspecting we might be, as has been mentioned in the media and on a number of websites, we might be being led up the proverbial garden path, 6mp's is adequate, 8 to 10mps if you must, anything above this is stretching the less than full size sensor??? 6mp's is adequate on A4 and if 300ppi, potentially contains as much information as a 10-12mp's, 300ppi image, the only difference is printable size.

 

Quality of processing, sensor type etc, is another issue entirely.

 

SW

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now i am totally confused.

 

The other day i was out and about and down at my local marina.

 

i was shooting jpg and raw. camera is Nikon D40X

 

after reading your post i opened the jpg in PS, Pic size 1.14mbs, then i looked at image size, resolution 300ppi pic size 3872 x 2592

 

then i opened same pic in PS only nef, size 9.4mbs looked at it in image size resolution 240 ppi . pic size 3872 x 2592.

 

so are we talking about different things, if so what are they.

 

 

yours in confusion Fred

Edited by Clifftop

my mind not only wanders-- sometimes it leaves completely.

 

 

Updated 7/3/09

http://sites.google.com/site/pomfred/

 

 

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The DPI figure is not an attribute of the image data, it's a bit of metadata tagged onto the image as a hint to those bits of software that care. For instance, this bit of C# code will load an image and save two copies, identical in every way except that one claims to be 300 dpi and one claims to be 10dpi:

 

		static void Main(string[] args)		{			string source = @"I:\Documents and Settings\steve\My Documents\My Pictures\elise\IMG_0324.jpg";			string targetLow = @"C:\lowres.jpg";			string targetHigh = @"c:\highres.jpg";			Bitmap bmp = new Bitmap(source);			bmp.SetResolution(300, 300);			bmp.Save(targetHigh);			bmp.SetResolution(10, 10);			bmp.Save(targetLow);			bmp.Dispose();		}

 

And you get

 

Original:

 

IMG_0324.jpg

 

300dpi:

 

highres.jpg

 

10dpi:

 

lowres.jpg

 

All the same, unless you load them up and examine the image properties, and all just as crap as the original.

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now i am totally confused.

 

The other day i was out and about and down at my local marina.

 

i was shooting jpg and raw. camera is Nikon D40X

 

after reading your post i opened the jpg in PS, Pic size 1.14mbs, then i looked at image size, resolution 300ppi pic size 3872 x 2592

 

then i opened same pic in PS only nef, size 9.4mbs looked at it in image size resolution 240 ppi . pic size 3872 x 2592.

 

so are we talking about different things, if so what are they.

 

 

yours in confusion Fred

 

I would read the as the program sees it as 240ppi in nef (RAW) As I dont shoot in raw at all, I dont know or have an issue? I wonder, did you try to re set the PS box to 300ppi?

 

. . . OK Just tried it, I'm now confused myself, cos you can adjust the 'ppi' up!!! I put a 'RAW-nef' image up to 600ppi!!! Begs the question is 240 the ppi rate that 'nef' is set to in the camera or is it the way PS defaults? :huh:

 

A can of worms or what . . . :headhurt: SW

 

PS, I'm just going to bounce along, with the basic knowledge . . . for get the techie stuff, and enjoy my photography, seem to remember Ken Rockwell got into this a bit deeply on the issue of D40 v D40X v D80. I think it 'hung' there as well, with most individuals, with Ken singing the praises of the D40, and its 6mp's. He maintained the higher 10mp rating was no better, even worse, (slower camera processing!) than the poultry 6mp of the D40. :wallbash: O'boy . . .

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The DPI figure is not an attribute of the image data, it's a bit of metadata tagged onto the image as a hint to those bits of software that care. For instance, this bit of C# code will load an image and save two copies, identical in every way except that one claims to be 300 dpi and one claims to be 10dpi:

 

		static void Main(string[] args)		{			string source = @"I:\Documents and Settings\steve\My Documents\My Pictures\elise\IMG_0324.jpg";			string targetLow = @"C:\lowres.jpg";			string targetHigh = @"c:\highres.jpg";			Bitmap bmp = new Bitmap(source);			bmp.SetResolution(300, 300);			bmp.Save(targetHigh);			bmp.SetResolution(10, 10);			bmp.Save(targetLow);			bmp.Dispose();		}

 

And you get

 

All the same, unless you load them up and examine the image properties, and all just as crap as the original.

 

 

There you go, its smoke and mirrors . . . As my last post, I started to suspect . . . program related? I'm a happy man, thanks Steve Walker . . . :rolleyes:

 

SW

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