Long discussion on DPI


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#1
Originally posted by Jed
I say again, as someone who regularly gets published in over a dozen national boardsheets and tabloids, forget dpi.
Dude u can't print a 10 pixel by 10 pixel 72dpi image on a A3 sized 300dpi offset print. The quality is terrible!
 

Jed

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#2
No, and you can't print a rubbish worthless 10mp image to 2" square in a newspaper either.

I've seen pushed EI1600 2mp files printed to 16" x 16" on the front of one of the biggest selling Sunday broadsheets in the world. That works out to less than 72dpi.

At the end of the day like i said, newspapers are in the business of news.
 

#3
Originally posted by lyrrad


Dude u can't print a 10 pixel by 10 pixel 72dpi image on a A3 sized 300dpi offset print. The quality is terrible!
There's no such thing as a 10x10px 72dpi file on A3 sized 300dpi offset.

10 x 10 pixels at 72dpi works out to only a mere 1/7" by 1/7".
The same 10 x 10 pixel file at 300dpi is 1/30 by 1/30", not A3. So that's not possible anyway. But you can have 2 megapixel (1800x1200) files full page, no problems.

Regards
CK
 

denizenx

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#4
screen dpi is 72, 96, 120. 3 common sizes depending on roughly your resolution on a what-size monitor...

I think Jed is just saying that if a picture is usable it doesn't have to be Vogue-quality to make the front page.

I think YSLee shd relax, stop trolling ppl.
 

#5
I've seen it happen before. Maybe not at the exagerated dimensions I gave. But I've seen people trying to stretch 72 dpi images, with small 2cm by 1cm print dimensions onto 300dpi magazine print ads, and articles. It's horrible! All jagged and pixelised.

Originally posted by ckiang


There's no such thing as a 10x10px 72dpi file on A3 sized 300dpi offset.

10 x 10 pixels at 72dpi works out to only a mere 1/7" by 1/7".
The same 10 x 10 pixel file at 300dpi is 1/30 by 1/30", not A3. So that's not possible anyway. But you can have 2 megapixel (1800x1200) files full page, no problems.

Regards
CK
 

Zerstorer

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#6
Originally posted by denizenx
screen dpi is 72, 96, 120. 3 common sizes depending on roughly your resolution on a what-size monitor...
:thumbsup:

Yep, denizenx is right about this. 72dpi is just an often quoted number for screen dpi, actual dpi count depends on your resolution and size of your monitor.

For my 19" actual screen dpi ranges from 80+dpi(1280x960) to ~103dpi(1600x1200)
 

mpenza

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#7
Originally posted by ckiang
There's no such thing as a 10x10px 72dpi file on A3 sized 300dpi offset.

10 x 10 pixels at 72dpi works out to only a mere 1/7" by 1/7".
The same 10 x 10 pixel file at 300dpi is 1/30 by 1/30", not A3. So that's not possible anyway. But you can have 2 megapixel (1800x1200) files full page, no problems.

Regards
CK
Many people are still confused by image resolution vs print resolution ;p
 

denizenx

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#9
Originally posted by lyrrad
I've seen it happen before. Maybe not at the exagerated dimensions I gave. But I've seen people trying to stretch 72 dpi images, with small 2cm by 1cm print dimensions onto 300dpi magazine print ads, and articles. It's horrible! All jagged and pixelised.

those are the cheap ads I guess, like Life or Computer Times sometimes take press release shots and up the rez... but here I wd object to the quality... it just smacks of plain laziness.
 

mpenza

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#10
Originally posted by lyrrad
I've seen it happen before. Maybe not at the exagerated dimensions I gave. But I've seen people trying to stretch 72 dpi images, with small 2cm by 1cm print dimensions onto 300dpi magazine print ads, and articles. It's horrible! All jagged and pixelised.

This makes sense. The original "10 pixel by 10 pixel 72dpi image on a A3 sized 300dpi offset print" is a tad misleading and Jed definitely doesn't mean using a 10x10 pic to blow up ;p

10x10 is already the resolution of the image. There's no need for a "72DPI" thingie if printsize is not mentioned.
 

#11
What I always do is resize my images to 72dpi first then, resize the screen dimensions accordingly. It's no point to download say a 180dpi 1280x1024 image from a digicam, leave it at 180dpi and resize it to 640x480. The monitor won't pick up the extra 'dpi'.

So screen / Internet working reso is normally 72dpi.

And to confuse the matter further, when we work in print we scan in say 500dpi, work on the image. Then drop it to 300 dpi if we're printing high res or 180 or 150 dpi on mid res; depending on the job.

If I'm not mistakened, I think TV broadcast (not high def) is less then 72dpi and less then 720x576.

Originally posted by Zerstorer
:thumbsup:

Yep, denizenx is right about this. 72dpi is just an often quoted number for screen dpi, actual dpi count depends on your resolution and size of your monitor.

For my 19" actual screen dpi ranges from 80+dpi(1280x960) to ~103dpi(1600x1200)
 

mpenza

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#12
Originally posted by maddog


as in size of pixel not equal to ink dot?
that's probably another story (especially for inkjets). anyway, for a digital image, "DPI" doesn't make much sense if no print size is involved. e.g., you don't have to say a 1200x1800 pic is 300DPI. The resulting print resolution is only 300DPI when the 1200x1800 pic is printed 4R. If you print it at other sizes, it won't be 300DPI.
 

Zerstorer

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#13
Originally posted by lyrrad
What I always do is resize my images to 72dpi first then, resize the screen dimensions accordingly. It's no point to download say a 180dpi 1280x1024 image from a digicam, leave it at 180dpi and resize it to 640x480. The monitor won't pick up the extra 'dpi'.

So screen / Internet working reso is normally 72dpi.

There is no such thing as a 180dpi 1280x1024 image.

The is a "DPI" only when you factor in the size of the display format(whether print or monitor).

Try viewing 640x480 image at 640x480 and then at 1600x1200.

By your reasoning it should look the same since its' a 640x480 "72dpi" image. Unfortunately, it will look much less grainy at 1600x1200, albeit smaller.
 

mpenza

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#14
Originally posted by lyrrad
What I always do is resize my images to 72dpi first then, resize the screen dimensions accordingly. It's no point to download say a 180dpi 1280x1024 image from a digicam, leave it at 180dpi and resize it to 640x480. The monitor won't pick up the extra 'dpi'.
This is really unnecessary ;p Do note that the important "dimensions" is the 1280x1024, rather than the DPI.

Hopefully, you didn't have to repeat the process everytime you change to a bigger monitor.
 

Zerstorer

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#15
Originally posted by lyrrad

If I'm not mistakened, I think TV broadcast (not high def) is less then 72dpi and less then 720x576.

There is no DPI.

You only consider the resolution of the source(horizontal x vertical pixels).

Divide each dimension by the width and height of the display and you will get your DPI.(any interpolation or bilinear/bicubic stretching performed to fill the output display is not counted).
 

denizenx

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#16
Originally posted by maddog


as in size of pixel not equal to ink dot?
image resolution is same as whatever resolution what... image SIZE is diff..

so 1600x1200 at 300dpi is still 4x bigger than 800x600 at 300 dpi.
and 800x600 at 150dpi shd be the same as the 1k6x1k2 at 300. here the pixel/ink drop size changed. BUT as a printout do u think the human can tell if this pixel had been rescaled 400% at 150 dpi or the image upsized to 300dpi?

too much AI in our software I think... if u specify 300dpi and 16"x 12" printout in PS see ur image size jump into humongous dimensions... ie ur 10x10 wd become 300x16 X 300x12... and look like shit
 

mpenza

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#17
Originally posted by Zerstorer


There is no DPI.

You only consider the resolution of the source(horizontal x vertical pixels).

Divide each dimension by the width and height of the display and you will get your DPI.(any interpolation or bilinear/bicubic stretching performed to fill the output display is not counted).
His assumption is that every TV screen in the world measures roughly 8 inches by 10 inches.... but seems like the world has moved on....
 

denizenx

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#18
pal and ntsc got diff vert res, one is 600x500 the other ntsc is 7xx iirc... hence last time those old TV sets got sync probs... but new electronics can just reclock and hey it's a MKTG FEATURE..

dun think about dpi unless printing.. hence all jpegs default is 72dpi (std monitor)

easy example is to load a jpg on screen with IE or some simple non-PS/AI/FH prog and just change ur res around... if the picture stays the same size then wow ur video card is good...
 

#19
Why is there no such thing as a 1280x1024 180dpi image?

And no it won't look the same because when u created the image, lets say in PS as a PSD file, u set the pixel size to 640x480.

Let me use vectors vs raster images example.

Here we are talking about raster images. Where the file is described as pixels. Each pixel within the 640x480 holds a bit of information. So stretchin the image to 1600x1200 increases it wat? 2.5 times? So every 2.5 pixels (if tt is possible) carries the same info.

Wheras in vector images, image is described by mathematical calculations of points on the screen. Therefore, the image retains its 'quality' in spite of the size it is stretched or shrunk to.

Originally posted by Zerstorer


There is no such thing as a 180dpi 1280x1024 image.

The is a "DPI" only when you factor in the size of the display format(whether print or monitor).

Try viewing 640x480 image at 640x480 and then at 1600x1200.

By your reasoning it should look the same since its' a 640x480 "72dpi" image. Unfortunately, it will look much less grainy at 1600x1200, albeit smaller.
 

mpenza

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#20
You're right in that we're talking about raster images and DPI doesn't make sense if no printsize is specified.

Unless you mean you digicam produce vector images.... and even then does DPI make sense since you mention stretching and shrinking a vector image retains it's quality?
 

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