DPI: camera versus scanner?

[ric1]

<p>Hi,</p>

<p>Why are my scanner jpgs 300dpi while my Canon EOS-300D jpegs are only 180dpi please?</p>

<p>Thanks,</p>

<p>Ric</p>

[mike dixon]

Somewhere in the software/firmware of each device is a default setting for the DPI value it assigns to jpgs. Those values happen to be different in your scanner and in your camera. They have absolutely no effect on the resolution or quality of the jpg. The DPI of a file only makes a difference when printing.

[ric1]

<p>Thanks.</p>

<p>This is an issue for me. Everytime I submit an image for publication I get an editorial "gotta be 300dpi", can I reset the default in my camera maybe?</p>

[Spearhead]

<p>Mike's right, it's not relevant. Even when printing, it may not matter since most printers now figure it out. The resolution of your file is the number of pixels in one direction by the number of pixels in the other direction. Since there are no inches in digital files, "dpi" is completely meaningless.</p>

[mike dixon]

I'm not familiar enough with the 300D to know whether you can change the camera default. You can, however, change the file's DPI in just about any image editing program.

[James G. Dainis]

"gotta be 300dpi"? I would send them this:<P>

 

<center><img src="http://jdainis.com/300ppi_cannon_tiny.jpg"></center><P>

 

There you go. A nice 300 dpi image just like you asked.

[James G. Dainis]

Of course, I am not serious, not unless I just wanted to show the submission editor what a fool he was and didn't care about having an image accepted.

 

A while back a person asked what to do since the only submission guideline received was that an image had to have a "resolution" * of 300 dpi. Since the norm for prints is 10 x 8 inches it was suggested that the image should be at least 3000 x 2400 pixels with that meaningless 300 dpi tag attached.

 

* resolution in quotes since dpi has nothing to do with resolution.

[jcuknz]

<p>Having used my camera to copy things as my old scanner is not compatible with my new desktop I worked out that in fact it has quite a good 'dpi' or 'ppi'. This was less so when I copied some old quarter plate negatiives and the some 5x4 ditto. If the camera has a resolution of 4000 pixels across then when you copy a 35mm slide of 36mm across of roughly say 1.5 inches you are copying at 4000/1.5 or 2666ppi ... less impressive for the 5x4 when 4000/5 gives us 800 ppi ... but they looked quite reasonable for scenes taken sixty years ago :-)<br>

You could politely point out to the editor that you have supplied [ie.]3300 pixels across which is good for a 10 inch across print in his magazine at 300dpi.* Or else you can re-sample the file setting 300dpi FIRST and then the size you want him to get and it will read out for him at 300dpi. The man is a typical ignorant magazine editor without a clue :-) But we csannot tell him that if we want to do business with him .... fortunately I have never struck this with photos I have sold :-) My sympathies are with you :-)<br>

* if he want to print bigger the go back to your editor and enter 300dpi first and then the size he aims to print to and the resampling/interpolation part of the computer will create extra pixels to maintain his requirement.</p>

[frank_skomial]

<p>DPI image resolution is a place in image file format. <br>

It is a place holder for data, in all image format files, be it JPG, TIFF, etc. Usually 2 bytes of storage is dedicated for DPI, but that is file format dependent.<br>

It could be any value, including zero, or up to the max value the usual 2 bytes of storage can hold, e.g. 32767/32768.</p>

<p>The data there could be anything, and usually is meaningless -but sometimes it is importat - depends on the file creation history, and intended file usage.</p>

<p>E.g. if a paper print is scanned, then the DPI value represents resolution of the scanner used at the time of scanning. It could give you valueable information how the scan was done, if a better resolution scan could be done, or a lesser resolution would work for whatever presentation means will be used.</p>

<p>If a camera creates image for a computer display, then any most probable value of display device resolution is used. For old monitors, that DPI was smaller, like 96, and for newer portable displays with retina, display resolution is much higher. Anyhow, that value is meaningless, since each display device scales the picture as needed and appropriate, and ingores whatever DPI value is recorded in the picture file.</p>

<p>With printers, DPI could be used, - depends how it is printed, or also could be ignored.<br>

Some printer drivers ignore DPI and take requested print quality and print size from a print dialog, totally ignoring whatever DPI value says. </p>

 

[craig_shearman1]

<p>300 dpi is the resolution generally considered required in order to make a print from a digital file that is equal in shaprness to a print made from a film negative or transparency. But it's fuzzy math, and 200 dpi is often sufficient, depending on how large the print is and how closely it will be viewed.<br /><br />Cameras (and scanners) don't create files that are 300 dpi, 200 dpi or any other dpi. Instead, they create a finite number of pixels, which can then be divided to see how many dpi you get at any given size.<br /><br />With your 300D, the full-resolution file is 2048 pixels by 3072 pixels. If you divide either of those by 300, you'll find that you can make a print up to about 7x10 inches at 300 dpi. That's close enough to make an 8x10 with no problem. If you go to an 11x14, you're dropping to about 220 dpi, and at 16x20 you're down to abot 150, but larger prints are normally viewed from farther away so you're OK.<br /><br />When a publication/lab/etc. says they need 300 dpi resolution, they almost always mean 300 at 8x10 inches, so your camera is fine for those purposes.<br /><br />As far as images coming out of your camera saying they are only 180 dpi, that's not entirely accurate. The files aren't being created at 180 or any other dpi. They are still the 3072x2048. the 180 is just referring to how many dots (or pixels) you would get at a certain size. If you printed the image at 11x17 inches you would in fact get 180 dpi. But if you printed it 1 inch wide, you would get 3072 dpi. At 72 dpi/ppi (the standard resolution on the web or a computer monitor) your image would be 42 inches wide.<br /><br />PhotoShop and most other editing programs have a setting under "Image Size" that lets you change either the dpi or inches to see what size your image can print at. If you look at your file with it on 180 Photoshop will show that it can go to 11x17. Change it to 300 and it will show you about 7x10. Play with other settings and it will change accordingly.<br /><br />Bottom line -- ignore the 180. It doesn't mean anything.<br /><br /></p>

[fmueller]

<p>Maximum size images coming out of a 300D are 3072px X 2048px. That's 180dpi if you make a print of about 17"x11"; or 300dpi if you make a print of about 10"x7"; or 600dpi if you make a print of about 5"x3.5".</p>

<p>If somebody complains about a 3072px X 2048px image - or even one that is somewhat cropped down from that size - because in the EXIF data it happens to say 180dpi, that person would probably be better qualified flipping burgers than play acting being an editor. Since people poorly qualified to perform the job they are paid to do rarely appreciate much needed tuition, it is better to refrain from attempts to educate them. Simply change 180dpi to a more desirable and equally meaningless number like 300dpi in any image processing software such as Photoshop or GIMP. As long as you make sure not to affect the actual resolution of 3072px X 2048px or thereabouts, nothing is changed, but everybody should be happy!</p>

[mendel_leisk]

<p>There's scanning dpi, and printing dpi (dots per inch). The latter's JUST a setting, a default for printing, easily changed. Scanning dpi's actually ppi (pixels per inch). So a scan at (say) 4000 ppi might have 300 dpi. Confused yet? ;)</p>

[ric1]

<p>Thanks to all. I was just curious about the 300 dpi thing because I submitted a cropped photograph to a publisher several years ago for a book cover. The image (excellent) was rejected because it <em>'wasn't 300 dpi - must be 300 dpi'.</em> I then tried several things to achieve the desired dpi - my scanner has a 300 dpi default - but the publisher still wasn't happy. Because there is so much confusion around dpi I think the publisher was using it as an excuse to be awkward, I think they wanted to use one of their own 'house images' for the cover instead of my creation in Photoshop Elelments, based on the cropped photograph. The arrangement fell through in the end and I published the book myself as an ebook with the original artwork as the cover.</p>

<p>But it's a live topic of course. Recently I was asked to scan a series of analogue prints to a magazine and was advised two images of each photograph, one of 300 and one of 72 dpi. Of course doing this in elements is a doddle on the Image Size setting.</p>

<p>I suppose if an editor wants a 300 dpi of one of my default 180 dpi digital camera jpegs I can just save a copy at 300 dpi in elements and use that.</p>

<p>Good information and thank you! :)</p>

[James G. Dainis]

Scanner dpi is sort of the opposite of printer dpi.<P>

 

A 10 x 8 inch print scanned <P>

 

at 300 dpi = 3000 x 2400 pixels.<P>

 

at 72 dpi = 720 x 576 pixels.<P>

 

I guess they wanted the latter for display on the web and the former to make prints from.

[ric1]

<p>That sounds about right, thanks.</p>