Resolution

[EOS_JD]

Things are becoming a bit more clear. I will have to play around a bit more to get my head around it completely.

i know it's difficult at first. Just remember the equation and all can be worked out easily.

Resolution= pixels/print size

Pixels = Print size/resolution

Resolution = pixels/print size

 

[ksmattfish]

What determines the resolution of an image.
When checking the resolution of 3 different images taken by 3 cameras.
Image 1 taken with a 3.1 mega pixel camera = 230dpi
Image 2 taken with a 4.1 mega pixel camera = 75dpi.
Image 3 taken with a 10.2 mega pixel camera = 240dpi.

Regarding the initial question, do you think that the in camera software is setting your official definition of dpi? Or is it using the term dpi in place of ppi?

I get what you are saying. The definition of "telephoto" is a lens that has an effective focal length longer than it's actual focal length, yet 99.9% of photogs use the term to describe any lens with a narrower than normal angle of view. That's wrong according to the official definition, but everyone knows what they mean.

EDIT: I just checked, and yes, I was wrong about CS2. Canon Digital Photo Pro still uses the term dpi.

 

[EOS_JD]

Regarding the initial question, do you think that the in camera software is setting your official definition of dpi? Or is it using the term dpi in place of ppi?

It seems different cameras produce different defaults but the number means nothing. All that matters is the number of pixels in the image. the dfn of dpi in this instance is absolutely 100% WRONG! Substitute for ppi. The image is made up of pixels not dots. i think Canon know these terms are mixed up and confusing and are going with what they see as the majority. Adobe has it correct.

I get what you are saying. The definition of "telephoto" is a lens that has an effective focal length longer than it's actual focal length, yet 99.9% of photogs use the term to describe any lens with a narrower than normal angle of view. That's wrong according to the official definition, but everyone knows what they mean.

A 50mm lens viewed on a 35mm camera gives a field of view similar to the human eye. In my view anything longer than this is classed as a telephoto lens.

The effect you described above in the defn is the crop effect of a digital camera with a smaller sensor than a FF 35mm film negative. You can't have a wide angle telephoto can you?!

Hope you get there with resolution.

 

[ksmattfish]

A 50mm lens viewed on a 35mm camera gives a field of view similar to the human eye. In my view anything longer than this is classed as a telephoto lens.

The effect you described above in the defn is the crop effect of a digital camera with a smaller sensor than a FF 35mm film negative. You can't have a wide angle telephoto can you?!

Format has nothing to do with it. I learned that before the term "megapixel" was invented. Pure trivia, it has no real application unless you are building lenses.

http://en.wikipedia.org/wiki/Telephoto_lens

A regular lens of a focal length that is longer than what is considered a normal lens is not necessarily a telephoto lens.

Anyway, I'll apologize for arguing with you. You are right, there should be a standard in the terminology. When I look at the metadata from my 20D in CS2 Bridge it lists "resolution" at "300 dpi"; if I open that file in Adobe CS2, and pull up a ruler, it will scale the ruler to 300 pixels per inch. I assume Canon is at fault there? From now on I will try to use the correct terminology.

 

[e999sam]

Regarding the initial question, do you think that the in camera software is setting your official definition of dpi? Or is it using the term dpi in place of ppi?


When I view a RAW file in my pictures resolution is only expressed as height and width e.g. 3872 x 2592.
If I browse using adobe bridge then under the meta data tab the dimensions are again 3872 x 2592, but the resolution is 240 dpi. If I then open the file in camera RAW the resolution is 240ppi and again it’s ppi when opened in Adobe Photoshop.

 

[EOS_JD]

Were we arguing?! :hugs:

I love a good discussion. And when we are both proven correct it makes it all the better. Wikipedia is truly the font of all knowledge. :lmao:

Didn't realise Bridge used dpi either! Canon and CaptureOne are two of the more popular conversion programs and they really should try and get ths right to save more confusion.

cheers
Jim

Format has nothing to do with it. I learned that before the term "megapixel" was invented. Pure trivia, it has no real application unless you are building lenses.

http://en.wikipedia.org/wiki/Telephoto_lens



Anyway, I'll apologize for arguing with you. You are right, there should be a standard in the terminology. When I look at the metadata from my 20D in CS2 Bridge it lists "resolution" at "300 dpi"; if I open that file in Adobe CS2, and pull up a ruler, it will scale the ruler to 300 pixels per inch. I assume Canon is at fault there? From now on I will try to use the correct terminology.

 

[EOS_JD]

just remember that the ppi/dpi figure means nothing until you are ready to print. then use the formula above to get the resolution you want or the correct number of pixels.

If you have 8Mp+ I suggest anything up to A4 is printed anywhere between 240pp-300ppi 9so that's your 6x4s and 10x8s etc.

If you need bigger switch off the resample button so the pixel number stays the same and increase the print size. At 19x13 I get 179.666ppi from my 20D files.

If you need bigger than this I'd suggest clicking the resample button and inserting the resolution as about 180ppi and manually enter the image size say 20x16 or something like that.

photoshop should do a decent job of resampling although there are other programs that will do this for you.

cheers
Jim

 

[Torus34]

Thanks to all for the corrections and amplifications to my original post. I love to learn, and this has provided me with an excellent opportunity.

Now, a question:

This forum has a section devoted to articles about various photographic topics. One of the nice things about articles is that they can cover a subject in considerable detail. A second nice thing is that once an article exists, some questions can be answered by simply posting a link to it, rather than going over the same ground again and again whenever a new person posts the same questions.

You know where this is going, right?

Pixel, ppi, dpi and resolution come up again and again.

Who's going to step up and volunteer to write a good article covering the topic? Several of you are far better equipped to do it than I am. If you wish to explore this without fully committing yourself, let Terri know and she'll fill you in on the how-to's.

 

[Stevedevil]

I must agree, this topic has had a great response from some extremely knowledgable people...:hail:

 

[EOS_JD]

You know the ppi/dpi/resolution thing is VERY simple to understand once grasped.

Images are made of pixels therefore ppi
Printers print dots of ink on the paper so dpi

Higher generally equals better quality (to a point)

 

[EOS_JD]

Can I also say that Adobe Bridge has been amended in CS3 to show ppi. I was at work earlier and couldn't check but CS2 does show dpi!!!

The CS3 Bridge looks nicer and has corrected their error.

Cheers
Jim

 

[fotogenik]

just remember that the ppi/dpi figure means nothing until you are ready to print. then use the formula above to get the resolution you want or the correct number of pixels.

If you have 8Mp+ I suggest anything up to A4 is printed anywhere between 240pp-300ppi 9so that's your 6x4s and 10x8s etc.

If you need bigger switch off the resample button so the pixel number stays the same and increase the print size. At 19x13 I get 179.666ppi from my 20D files.

If you need bigger than this I'd suggest clicking the resample button and inserting the resolution as about 180ppi and manually enter the image size say 20x16 or something like that.

photoshop should do a decent job of resampling although there are other programs that will do this for you.

cheers
Jim

If it has nothing to do with anything until you print, then how do you deal with placing lo-res files on web pages.

When I decrease the resolution on an image I use the dpi setting in the image size dialog box to reduce the size of the images I place on the web.

Should be doing this in a different manner?

Cheers,

 

[markc]

If it has nothing to do with anything until you print, then how do you deal with placing lo-res files on web pages.

When I decrease the resolution on an image I use the dpi setting in the image size dialog box to reduce the size of the images I place on the web.

Should be doing this in a different manner?

Cheers,

You must also be changing the pixel count if that is happening. To see that changing just DPI/PPI has no effect on the digital file itself, make sure that "resample" is off. You can then change the image size in inches and the PPI as much as you want, but the pixel count never changes.

Saying that a high DPI or PPI determines quality is like saying that miles per gallon determines how far you can drive. Sure, it's a measure, but if you have a 50 MPG car and a 2 gallon tank, you aren't going that far. A 20 MPG car with a 20 gallon tank is going to do you much better. You need the whole story.

A PPI count is only valid for the print size that is stated in the dialog. If you have 300 PPI for 8"x12", then that 300 PPI is only valid if the image is actually 8"x12" when displayed. That's easy for a print, but a monitor will show the image based on the monitor's resolution which will vary quite a bit. It's Pixels Per INCH. You need to know how many inches for it to mean anything. [Insert size matters joke here]

If you are sizing for the web, you have to guess at what size is best, as everyone seems to have a different monitor resolution. 800x600 used to be a good guess, as people rarely went off the defaults. I personally assume bigger. If someone is using a 1280x1024, then an image size of 800x600 fits with enough room for the rest of a web page around it. On the web (and in any digital form), pixel count rules, not PPI.

This can be a pain to get your brain wrapped around. I think if you are having trouble, you have to let go of some assumptions of what you think is going on and try coming at it from a different angle.

 

[fmw]

DPI is also used in scanning. Not just in printing.

 

[markc]

DPI is also used in scanning. Not just in printing.

Yup, although that's another place where they misname it. It should be PPI, as you are getting pixels, not ink dots. For scanning, comparing one PPI to another for the same image gives you a good indication of comparative quality, as the image size stays fixed. For film, you want to get into several thousand PPI, but for prints, generally anything over 300 is a waste. Prints don't have high definition.