dots per inch

[jb123]

how many dots per inch if you print. the photo is taken raw or large on a 10D. Photoshop 180 pixels per inch.
What is that in dots per inch on print

[robertwgross]

The 10D files cover roughly 6 megapixels (3072x2048). If you do the math at 180 DPI, that yields about 16 inches on the long side.

---Bob Gross---

[jb123]

sorry still do not understand the dpi very well. If I print A4 size from a raw file how many dpi will it print or do I set the dpi myself on the printer

[blue_max]

Dots per inch is just a measure of how dense the dots (pixels) are packed into a given space.

In photoshop or similar, you can adjust the dpi and size. If you increase the dimensions, the dpi will reduce. You can retain the dpi, but the software has to add the additional information by second guessing the required pixels that are missing. This is known as interpolation and is not good.

I think of it as a chess board with the squares being the pixels. If one was to compress the board, there would be more pixels per square inch, but the size would be smaller. There are however, the same number of squares. To make the board back to the original size and retain the more compressed pixels, one would have to add squares and this is where the interpolation comes in.

It's not easy to grasp, or to explain! Maybe think of it as butter on toast, spread it thin and it goes further. Trowel it on and it doesn't go far. But its the same amount of butter, just the density that changes.

The camera file is just pixels. You can spread it out and have lower pixels per inch or pack it smaller and have higher.

Normally it doesn't make too much difference. But a printer needs a certain amount of information to render the picture with sufficient detail.

Traditional printing will require generally at least 300dpi. A laser or inkjet can get away with around half that (150dpi). If you change the dpi setting in photoshop you will see the size change (if you fix the file size).

In a nutshell, a 6megapixel image will be good for an A4 print on a laser/inkjet.

Graham

[rdenney]

sorry still do not understand the dpi very well. If I print A4 size from a raw file how many dpi will it print or do I set the dpi myself on the printer

You can't send a raw file directly to the printer (at least not my printer). You'll have to convert from raw first, either using Canon's software, Photoshop, Breezebrowser, Rawshooter, or whatever. In Photoshop, you can set the pixels/inch in the software to yield the print size that you want, and then just send it to the printer. If that pixels/inch parameter in your software is less than about 240, the image quality may suffer a bit down to a working minimum of 150 or 180. In any case, it's a setting in the software you use to make the print.

What may be confusing you is that printers build up pixels with an array of dots, and those two terms get mixed up. Thus, the Epson printer you buy will claim 2880 dots/inch, but it will take a good-size array of dots to accurately print a pixel. Thus, you'll still need a minimum of 150 and optimally at least 240 pixels per inch of print to get good quality.

Rick "thinking dots and pixels have often been confused" Denney

[erik-nl]

A digital picture in a computer has no 'real world' dimensions. No inches, no feet, no meters, nothing.
Such a picture really is just an arrangement of bits and bytes that can be interpreted as 'picture elements' or pixels by suitable software running on that computer.
That software can read those bits and bytes and make a computer monitor project a visible image, more or less as intended, or it can send instructions to a printer.
The only 'dimensions' a digital picture in a computer has are the exact number of pixels it is made of.

The 'Pixels per inch' rate mentioned by editing programs like Photoshop has no influence on printing dimensions at all, only the actual number of vertical and horizontal pixels has.
It's only practical use is to help calculate how large a print will be when printed by a printer with a known DPI-rate. Without actually changing the number of pixels it is made of, you can easily change the PPI-rate of a picture with an editing program, just to see how big it will come out of your printer.
Only changing the horizontal and vertical number of pixels will make a picture really 'smaller' or 'bigger' than it was before. This is generally done using a 'scaling' command.

Most printers of photographic quality will print (about) 300 dots per inch horizontally and vertically.
When printed by such a printer a .jpg (or .tif or .bpm) file of 3072x2040 pixels will become (3072/300=) 10.24 inches by (2040/300=) 6.8 inches on paper.

How large your prints will be of a certain .jpg file therefore depends intirely on the printer you use.

[BlueTit]

erik-nl if I understand you correct then, better printers will print the same photo smaller at higher dpi, am I reading that correctly?

I am still getting my head around elements and dpi and pixels etc is just too much at the moment.

[erik-nl]

A good printer will be capable of printing more pixels per inch accurately than a lesser one.
A setting of 300 dots per inch will, with a good printer, result in a print that is sharp and detailed even when viewed with your nose nearly touching the paper.
If you want a print of such a high resolution then six megapixels will not give you a very large print.

If you want a larger print from your six megapixel file you will have to reduce the number of pixels per inch printed.
With a printersetting of 150 dots per inch your six megapixels will give you a print twice as big, but when viewed 'at noselength' it will look terrible!
With a printersetting of 75 dots per inch you can make a really big poster, but when viewed 'at noselength' it will now be difficult to recognize any detail at all.

The only way to get a larger print with the same amount of detail when viewed from a given distance is to increase the number of pixels generated by the camera. Thus a 8 megapixel camera instead of a 6 megapixel one, or a twelve or sixteen megapixel one.

[robertwgross]

If you are trying to print something small, like a print of 4x6 inches, then 300 DPI is a very high quality print standard. Some commercial printers produce worse than that.

If you start in around a print of 11x14 inches, then your camera's 6 megapixel image won't be adequate for meeting that 300 DPI standard. No problem. Print it with 240 or 200 DPI or whatever you have. Does this mean that the 11x14 print will look bad? No. That is because as the print size gets larger, it is assumed that your viewing distance increases. The very minimum viewing distance for a print is the diagonal dimension across the print.

As you go larger and larger, you may reduce to a 150 DPI, or 100 DPI quality. No problem.

---Bob Gross---

[lostdoggy]

This may help:
http://www.luminous-landscape.com/tutorials/understanding-series/res-demyst.shtml

[Titus213]

Actually the ability of the eye to see the DPI comes in to play at some point.
From Luminous Landscape:

To understand these issues clearly one needs to start with an acceptance of certain physical limitations of the human eye. Our vision is incapable of discriminating detail below a certain level. This varies from individual to individual and even by the same individual on different days, but more or less this point is at about 200 dots per inch ( 80 dots / centimeter).

YMMV

Check out this

http://www.luminous-landscape.com/tutorials/understanding-series/und_resolution.shtml

[griff2]

Dots per inch (DPI) or pixels per inch (PPI) are just a measure of how big the pixels are, which will then relate to how many of them will fit in an inch. The higher the DPI or PPI the smaller the pixels so the greater the resolution. Anything above 300dpi is regarded as photo quality. This means that the largest print you can make at 300 DPI/PPI from the 10D is ~10 x 7 inches. Of course, you would probably get away with a lower dpi and still get satisfactory results, and if you would be viewing from a distance, could quite significantly lower the dot pitch.

[pwaite]

Interested that JB123 says his 10D gives 180dpi but the 20D gives 72 dpi . Why is there the difference?

[lostdoggy]

The camera doesn't really give you DPI its when you convert that it will change. Unlesss you are talking JPEG from the 20D. If you shoot in RAW and did the conversion in say DPP then the default will be 350DPI but you can change that to whatever you want up to a limit. If you did it in say PhaseOne C1 then the default will be 300DPI, again that is not set in stone.

[Movick]

I’ve personally found using the digital scaling program Extensis pxl Smartscale 1 extremely effective for creating enlargements of outstanding quality for print. Before the purchase of my new 1Ds MkII, I used a 4 mp Olympus E-10 extensively for all kinds of print work, including significant enlargements for high-quality, photographic package labeling and commercial posters. Six mega-pixels (10 D) can capture more than adequate detail to be enlarged to virtually any desired size with the right imaging program. Try the 30 day demo and see what you think. I can’t live without it; even with my 16 mega-pixel 1Ds MkII!



http://www.extensis.com/en/products/product_family.jsp?locale=en_US&id=prod120009



Movick

[chris clements]

Every digital camera just produces the 'dot'. Dots have no physical size until you (through your software) decide how many of them to squeeze into each inch on the paper. 300dpi to satisfy critical magazine editors, but around 200 dpi will pass muster In most other cases.
So in practice, if you've got a 6/8 mp camera you don't need to worry about the dpi figure at all until you're wanting to print well above A4 size - closing in on A3 or bigger.

Remember that printers define dpi differently. A single 'dot' from the camera could be made up of 6 (or 8, etc) different colour 'dots' from the printer, depending on how many ink tanks it has. Printers always quote this higher number. So, to achieve 300 'true' dpi on the paper, your 6-ink printer would have to be capable of 1800 dpi or better.

[Salleke]

how many dots per inch if you print. the photo is taken raw or large on a 10D. Photoshop 180 pixels per inch.
What is that in dots per inch on print

A very intresting link that explain dots per inch and other related items.
Go also to the home page of this link and see all the good articles about this subject.
I hope this helps you in understanding and finds answers to your questions.


http://www.scantips.com/basics02.html