dpi?


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melvin

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wats the meaning on dpi? meaning of 300dpi? :dunno:
 

lsisaxon

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melvin said:
wats the meaning on dpi? meaning of 300dpi? :dunno:
dpi only makes sense when it is used in conjunction with an image output. How much information an image has is determined by the number of pixels in the total picture.

On an output, for example a print, the dpi will determine how fine the details will appear. This has to do with how far you are going to view the image from. However, how much details it can contain or how large the print can go is still determined by the number of pixels the image contains.

Now for some simple arithmetics. Taking a 4R (4"x6") print as an example, in order not to see the dots, the dpi must be more than 200, typically it is 300dpi. So
to give the best details, the number of pixels you should have must be at least 4"x300dpi x 6"x300dpi = 1200 dots (pixels) x 1800 dots (pixels) ~= 2.2mp.

If you want to print to a bigger size, for simplicity, we take 8" x 12" (double the length), a 2.2mp image can only produce a 150dpi (1800/12 or 1200/8). It would mean that you wold need to stand further away from the print in order not to see the individual pixels.
 

Snoweagle

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#6
lsisaxon said:
dpi only makes sense when it is used in conjunction with an image output. How much information an image has is determined by the number of pixels in the total picture.

On an output, for example a print, the dpi will determine how fine the details will appear. This has to do with how far you are going to view the image from. However, how much details it can contain or how large the print can go is still determined by the number of pixels the image contains.

Now for some simple arithmetics. Taking a 4R (4"x6") print as an example, in order not to see the dots, the dpi must be more than 200, typically it is 300dpi. So
to give the best details, the number of pixels you should have must be at least 4"x300dpi x 6"x300dpi = 1200 dots (pixels) x 1800 dots (pixels) ~= 2.2mp.

If you want to print to a bigger size, for simplicity, we take 8" x 12" (double the length), a 2.2mp image can only produce a 150dpi (1800/12 or 1200/8). It would mean that you wold need to stand further away from the print in order not to see the individual pixels.
Typically when i print or scan my pictures or other documents, i always but it to 300dpi, sometimes 600 hehe :cool:
 

melvin

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#7
Thanks guys for the enlightenment!:)

How can we tell from a pict that it is 300dpi or 600dpi?:dunno:

Does the dot varies in sizes? :dunno:

From our camera there are super fine, fine then there are large format, medium format .....etc .... meaning size of dot or they r not related at all? :sweat:
 

Mar 9, 2005
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i'm not sure about this, correct me if i'm wrong, but i think 'fine, normal, basic" refers to the compression, not the dpi.
 

jonnie84

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#9
melvin said:
Thanks guys for the enlightenment!:)

How can we tell from a pict that it is 300dpi or 600dpi?:dunno:

Does the dot varies in sizes? :dunno:

From our camera there are super fine, fine then there are large format, medium format .....etc .... meaning size of dot or they r not related at all? :sweat:
not sure how u tell... duno if can see the difference with the naked eye anot.

yeah the dot varies in size, i mean, if 300dpi, the dots gotta have a certain size, then at 600 dpi, it gotta fit twice the no. of dots in the same length, so of cos the dots gotta be smaller, or finer.

i'm not sure bout the camera settings on fine, normal. i think it's the compression too. those large format, medium format doesnt refer to dots at all. no relation.
 

lsisaxon

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AntiFruits said:
i'm not sure about this, correct me if i'm wrong, but i think 'fine, normal, basic" refers to the compression, not the dpi.
Yes. Fine, Normal and Basic refers to the amount of JPG compression.

To the rest who are still having problems with understanding dpi:
As far as the output from the camera is concerned, dpi should never be an issue because you are not outputting the image yet. What is more important is the image size, 3000x2000 etc.

And if you're really bent on knowing the dpi on the sensor, assuming it's a 6mp (3000x2000) DX size (23.5x15.6mm), the highest dpi is 3000/(23.5/25.4) = 3000/0.925 ~=3242dpi. Will you take that for an answer?

So please do not be too obsessed with dpi. So what if you have a 600dpi output if my input is only 1x1 pixels? You see the point there? (pun intended). The reason why the dpi is encoded in the jpg file is only to tell you the physical size of the image (in inches) if you are printing the image as the designated dpi (eg 300).
 

Verywierd

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#11
melvin said:
Thanks guys for the enlightenment!:)

How can we tell from a pict that it is 300dpi or 600dpi?:dunno:

Does the dot varies in sizes? :dunno:

From our camera there are super fine, fine then there are large format, medium format .....etc .... meaning size of dot or they r not related at all? :sweat:
If you open the image in an image viewer like Irfanview, ACDSee, Faststone etc, they usually have and option to view the image information or "size". Basically, if you view at 100% zoom or "full size" the 300 dpi image will be smaller than the 600 dpi image (of the same picture)

Anyway, here is another link that might make this subject a bit clearer.

http://www.danheller.com/tech-dpi.html
 

melvin

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#12
Verywierd said:
If you open the image in an image viewer like Irfanview, ACDSee, Faststone etc, they usually have and option to view the image information or "size". Basically, if you view at 100% zoom or "full size" the 300 dpi image will be smaller than the 600 dpi image (of the same picture)

Anyway, here is another link that might make this subject a bit clearer.

http://www.danheller.com/tech-dpi.html
Thanks guys!
Just wondering, how is it that the finer we set the bigger the file?
Sorry still learning!:sweat:
 

Verywierd

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#13
melvin said:
Thanks guys!
Just wondering, how is it that the finer we set the bigger the file?
Sorry still learning!:sweat:
OK. Silly example. Note that I am talking about JPEG ( .jpg) files only. When they say "fine" they mean smoother, more detailed.

Imagine that you are using 10 cent coins to draw a smilie face :) on the floor. Say you use 100 coins to draw a circle, 10 coins to draw each eye and 20 coins to draw the mouth. You should be able to draw a pretty clear smilie face with that. Take this as the "fine" setting and the file size is the total number of coins used (140).

Now, without changing the size of the smilie face, take away every other coin. That is, you now have a same size circle, but using only 50 coins, eyes with 5 coins and mouth with 10 coins. You will still be able to see a pretty good smilie face, but all the lines will be less smooth and more like ". . . ." instead of "........" . Take this as the "normal" setting. Notice that the number of coins used for the picture is a lot less i.e. the file size is smaller or "compressed".

You could keep doing this until you cannot see a proper smilie face any more.

JPEG is a "lossy" compression system, which means that it throws away some detail as part of the process used to make the file smaller, just like you threw away the coins in the example above. "Fine" will only have a small amount of detail lost and a bigger file, "Normal" more loss and a smaller file and so on.

Of course, this is a very simple example and if you start comparing "lossy" and "lossless" compression, this example will not work so well to explain the difference.

Hope this helps and does not confuse you even more :D
 

melvin

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#15
Verywierd said:
OK. Silly example. Note that I am talking about JPEG ( .jpg) files only. When they say "fine" they mean smoother, more detailed.

Imagine that you are using 10 cent coins to draw a smilie face :) on the floor. Say you use 100 coins to draw a circle, 10 coins to draw each eye and 20 coins to draw the mouth. You should be able to draw a pretty clear smilie face with that. Take this as the "fine" setting and the file size is the total number of coins used (140).

Now, without changing the size of the smilie face, take away every other coin. That is, you now have a same size circle, but using only 50 coins, eyes with 5 coins and mouth with 10 coins. You will still be able to see a pretty good smilie face, but all the lines will be less smooth and more like ". . . ." instead of "........" . Take this as the "normal" setting. Notice that the number of coins used for the picture is a lot less i.e. the file size is smaller or "compressed".

You could keep doing this until you cannot see a proper smilie face any more.

JPEG is a "lossy" compression system, which means that it throws away some detail as part of the process used to make the file smaller, just like you threw away the coins in the example above. "Fine" will only have a small amount of detail lost and a bigger file, "Normal" more loss and a smaller file and so on.

Of course, this is a very simple example and if you start comparing "lossy" and "lossless" compression, this example will not work so well to explain the difference.

Hope this helps and does not confuse you even more :D
Thanks Bro! much clearer now on FINE n NORMAL!:)

So to confirm there r different size for dots? is it 300DPI 1 size n 600DPI another size?
 

Verywierd

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#16
melvin said:
Thanks Bro! much clearer now on FINE n NORMAL!:)

So to confirm there r different size for dots? is it 300DPI 1 size n 600DPI another size?
Yes, if you view the pictures on the same viewer and identical settings other than dpi. For instance, the following pictures are #1 at 300dpi at 1inch x 0.75inch, #2 at 600dpi at 1inch x 0.75inch. In other words, same size pic, but one with less dots than the other. By the way, the pic is mine, so no copyright problems (unless someone tries to use it without my consent) :)

#1


#2


As you see, #2 is bigger. This is because the dpi that your monitor displays is fixed e.g. 72 dpi. So, the only way the monitor can show a picture with more dpi than 72 is to make it bigger.

For example, the next picture #3 is set at 72dpi at 4.167inch x 3.125inch. However, on your screen it should look the same as #1 because the total number of dots inside is still the same.

#3


In know this is terribly confusing. Maybe this web page will explain it better than me.

http://www.ncsu.edu/sciencejunction/route/usetech/imagemanipulation/output.html
 

melvin

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#20
Thanks Verywierd got a much clearer picture now Thanks again!:D
 

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