photo resolution


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#1
How do you tell whether your photo is 300dpi in resolution? What kind of resolution in terms of pixels is needed for a 300dpi photo?

green horn here. thanks in advance. :)
 

ortega

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#2
for a 1" square image at 300dpi, you will need 300 pixels by 300 pixels

this same image is also 2" square at 150dpi
and 3" square at 100dpi
 

Lmodel

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#3
For most consumer digital cameras, the average resolution is always standing at 72pixels/inch which should be good enough for 3R to 8R development for most people.

For prosumers, I believe most can go up to 180pixels/inch and only people who are very specific on their sharpness go to such extends but it also increases in file size. You can develop up to A3 sizes and still maintain clarity.

For 300pixels/inch, we normally do it for catalogue printing or brochure printing. However, I'm not too sure for photos but I'm sure it'll defintely still be a clear when you blow it big.

Cheers
 

mpenza

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#4
Lmodel said:
For most consumer digital cameras, the average resolution is always standing at 72pixels/inch which should be good enough for 3R to 8R development for most people.
erm... incorrect. A 1.5MP (1500x1000) pic printed 3R is around 300DPI. Printed 8R, it's ~125DPI. The same pic printed at different sizes would result in different "DPI". A 1.5MP pic is only 72DPI when printed at 20.8 inches by 13.8 inches.
 

madison

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#6
mpenza,
thx for the link.

So in response to the query of this thread as to what kind of resolution in terms of pixels is needed for a 300dpi photo, I just extend ortega's explanation.

For a 1" square image at 300dpi, you will need 300 pixels by 300 pixels. For 4R, which is 6" x 4", you need:

6 x 300 = 1800 and 4 x 300 = 1200, i.e. 1,800 x 1,200.

So if u print a 4R photo that is lower than 1,800x1,200 u just have to accept lower dpi?
 

clicknick

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#8
Sorry, just a newbie questions on sending for printing. If I have a 6MP jpeg photo that is 180pixels per inch by default, do I need to use PS to change it to 300 pixels per inch first before i send it for printing at 4R size?

I am using several software for image editing. In some sw, it shows my pic as 180dpi, in PS it shows as pixels per inch. So dpi=pixels per inch?

Also, in reply to barracuda's question, I use photoshop elements, open the pic, image->resize->image size
Under document size: resolution: will show how many pixels per inch. To change, uncheck "resample image" first, then change to any value, eg 300.
 

#9
hi, thanks to those who have replied. the reason i ask this question is, to me, when you say a pic of xxx dpi resolution, it corresponds to a certain print size, if it is an 8" x 10" print, then to have 300 dpi, you need 2400 x 3000 resolution; if it is an 8" x 12" print, you need 2400 x 3600 instead.

some newspaper/mag, etc always asks for ppl to send pics of at least 300dpi, without saying the print size, that's why i am confused, or there is a standard/convention out there? :dunno:
 

sinlg

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#10
Is 300dpi the most optimal? Seems like consumer printers these days claim hugh DPIs (like 5000+)... so are we saying we can print better at home that the colour labs?
 

nemesis32

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#11
300dpi is a guide. Most printers only use abt 250dpi max and you won't know the diff. I doubt home printers have 5000dpi... Prob diff in terminology.
 

#12
nemesis32 said:
300dpi is a guide. Most printers only use abt 250dpi max and you won't know the diff. I doubt home printers have 5000dpi... Prob diff in terminology.
Inkjet "dpi" is different. Because inkjets use ink droplets and each pixel in the image needs far more than a single droplet of ink to form, the inkjet resolution needs to be very high. We've seen anything from 720 all the way to 5760. Some says the true resolution of these is actually the quoted res divided by the number of colours (cartridges). E.g. a 6-colour 1440dpi inkjet is there for 1440/6 = 240dpi. This is more than good enough for a good print.

Regards
CK
 

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