What size are they asking for?

[rpcrowe]

I don't want to seem stupid...

Petco Foundation is offering a contest for rescue and other groups who are asked to submit a story along with photographs of a particular animal that exemplifies the work the group does on behalf of animal welfare...

Applications will be evaluated on the quality o the story and photos submitted...

The stated requirements for photos are:

High quality photos are preferred (3648 pixels x 2736 pixels @ 72 dpi or 1-3 mb preferred)

My Canon 7D Raw image size is:

5184 x 3456 pixels at 240 Pixels per Inch or 22.5 mb

Reducing the pixels per inch to 72 results in 1555 x 1037 pixels

I don't know what they mean by dpi for a photo. I thought that was a printing term. How can I correlate the dpi requirement to ppi?

[dem]

3648x2736 jpeg

Note that the required 3 by 4 image aspect ratio is different from that of your sensor (2 by 3). Don't worry about dpi, "@72 dpi" does not make any sense in this context. I'd also ignore the "1-3 mb" bit.

[Kodiak]

Hi Richard,

• There are no stupid questions… only stupid answers!

• Your Canon 7D records RAW files (not pictures!)
• DPI vs PPI: the same idea applied to different technologies:
__ DPI, dot per inch, a dpi is the smallest linear part of a print.
__ PPI, pixel per inch, a ppi is the smallest linear part of a monitor screen.
So, dpi or ppi, in the final conversion they will be the same: one in paper
language the other in monitor screen language but they will not have the same size.
They may have the same ratio but not the same smallest linear part density (dpi or ppi)

Example: in PS all versions,
When you have finished your work in your software, you may edit the file size by selecting
"file/save for the web" or by selecting "image/image size" from the PS menu and enter the
desired final values prior to " save" or "save as" and your computer will do the math for you.

Am I bringing some clarity or more confusion?

[revi]

Unless they are just stating settings, talking about an image size in pixels 'at x dpi'
has no sense: size in pixels is independent of dpi... So I'd suggest don't worry about the DPI value,
you can set it to 72 to keep them happy, just make sure the size in pixels is what you want
(and ignore the size in cm/inch)

They won't like receiving a raw file, so you'll have to send a jpg And keeping it
below 3Mb at those pixel dimensions at highest quality is not guaranteed.

What I am wondering about: why do they want such very high resolution images,
and what rights do they want transferred to them?
Those are high quality print dimensions (think double page spreads), and at their
stated DPI, the long size would be over 50" ...

And about the DPI/PPI mess: it's even more complicated than kodiak stated:
-- there's at least two uses for DPI:
> in traditional book/magazine printing, 'DPI' (or lines per inch) corresponded to the
screens they use(d) to rasterise the image (normal values are 300 or 360 DPI),
> in inkjet printers DPI refers to the number of ink droplets deposited per inch, the
catch is that one 'pixel' corresponds to a square of several ink dots (thus allowing dithering),
so the actual detail in the printed image doesn't correspond to the indicated 'DPI' value.

As for PPI: not all devices use square pixels (TV), so the aspect ratio of the image
isn't always the same as the pixel ratio (Modern computer monitors do use square pixels afaik)

[george013]

I don't want to seem stupid...

Petco Foundation is offering a contest for rescue and other groups who are asked to submit a story along with photographs of a particular animal that exemplifies the work the group does on behalf of animal welfare...

Applications will be evaluated on the quality o the story and photos submitted...

The stated requirements for photos are:

High quality photos are preferred (3648 pixels x 2736 pixels @ 72 dpi or 1-3 mb preferred)

My Canon 7D Raw image size is:

5184 x 3456 pixels at 240 Pixels per Inch or 22.5 mb

Reducing the pixels per inch to 72 results in 1555 x 1037 pixels

I don't know what they mean by dpi for a photo. I thought that was a printing term. How can I correlate the dpi requirement to ppi?

This issue comes periodical.

The DPI is not a property of the photo but of the printer, monitor or whatever you use to view the photo.
If you look at the photo on a monitor with 96 PPI your photo will be sized (5184/96) x (3456/96) = 54 x 36 inch. To big for your screen, so you will have to scroll. This is a typicall 100% view.

The difference between ppi and dpi is that ppi is more physical based, dpi is more software based. The printhead spits 300 pieces of ink per inch on the paper, but the same printhead could also do 600. Every dot represents a pixel of your photo.
Your camera produces a photo of 5184 x 3456 pixels in RAW, that's the size of your sensor.
If they ask you a minimal size in pixels, thgan they want to print the photo at a certain format with their printer. The size of the photo in bytes tells something of the compression you used and is than also an aspect of the quality.

Looking at the figures they want to print a photo of 72x48inch or 183x122cm.

George

[jcuknz]

If I was entering the competition the two factors I would consider and work to is the format "3648 pixels x 2736 pixels ' or 4:3 apparently [ a simple crop and resize job] and working from your 22.5 file I would compress to 3Mb.....That is still quite a big file size for a quality image.

The rest is confusing garbage written by somebody who doesn't know what they are doing
A common occurance which I have read about numerous times over the years

[rpcrowe]

Thanks, my friends. I had considered ignoring the 72 DPI consideration. 1-3 mb is certainly not a "high quality photo. I have a hunch that whoever stated the size didn't know exactly what they were talking about... If they want to print really large, I would think that they would want 240-300 ppi...

[jcuknz]

I have three cameras with native resolutions of 76,180,and 300 dpi ... which is the best?
As it happened the Nikon with 300 dpi wins out over Canon and Panasonic I attribute that to conservative thinking at Nikon.
Whatever it is completely irrelevant to quality which depends on the pixels available not the dpi.
Since 150kb results in a good quality image on the web then 3Mb is I repeat plenty.
What is required largely depends on the viewing distance and this has been proved from time to time to confound the pundits
Else, ignoring content, how do hoardings usually look great from across the street.
This is one of the hoary old questions which appear from time to time to illustrate that people do not know what it is all about.

[xpatUSA]

Thanks, my friends. I had considered ignoring the 72 DPI consideration. 1-3 mb is certainly not a "high quality" photo. I have a hunch that whoever stated the size didn't know exactly what they were talking about... If they want to print really large, I would think that they would want 240-300 ppi...

Richard, I guess you know that the bigger the ppi, the smaller the print for a given pixel-sized image.

Reducing the pixels per inch to 72 results in 1555 x 1037 pixels

I was wondering how you did that? The reason I ask is that, as others have said, the ppi does not affect the pixel-size of the image unless you were using some sort of print preview application.

Just curious . . .

[jcuknz]

... If they want to print really large, I would think that they would want 240-300 ppi...

Sorry NO ... if they wanted to print 'big' they would ask for your 5184 x 3456 pixels and then interpolate to produce the pixels needed to print at 240-300 dpi. I used to use a 3.3Mp camera and all things equal would print at A3 size [ 48x29cm ] after interpolation in my editor ...

[dennybeall]

I think the people holding the contest just want to have pictures to compare that are just about the same size for their convenience. They are not photographers nor are they photography professors at the local college. Somebody had a picture and they liked the size so they stated that size as what they wanted.
If I take a large picture and pick the longest side and change the pixels to their longest number and change to 72dpi the size fits in OK on the one I tried the change with.