Join Now
Join ePHOTOzine, the friendliest photography community.
Upload photos, chat with photographers, win prizes and much more for free!
This may not be the right forum for this question but I have searched high and low for an answer to no avail.
I've copied a bunch of images from a friends Canon EOS 550D to prepare them for a slide show and I was surprised to find that the files were saved in the camera at 72ppi. From my understanding this is okay for web publishing but for printing I would expect a minimum of 150ppi. I note that the image size is much larger due to the CMOS sensor being that much larger. I have trawled through the manual and online yet have not found any information that allows the ppi size to be altered. My Nikons produce images with 300ppi.
My question is "Is this how the Canon EOS 550D saves files or have I missed something"?
Cheeers
Rob
I take it they are JPEGs....?
Any idea what your friends camera was set up like when the images where taken, Or are you looking at a preview sample.
I'm a Nikon bod myself, The other half has Canon DSLRs a 40D and a 5D MkII, Her files sizes and ppi output are similar to my Nikon cameras.
Sounds very odd to me......
Hi Cameracat, these files were taken directly from the SD card and plugged into my laptop. They are Jpegs and it was only as I was resizing them that I saw the ppi. I had a look at the camera but it only allows you to set the file size by dimensions where you get that quarter moon shape and L next to it.
The camera was brand new, the date hadn't been set and the file numbers started at 11 so I also find this odd.
As far as I know the camera has no concept of PPI - it just produces an image of whatever number of pixels by whatever number of pixels. How those pixels are spread out (ppi) is determined in the computer. 72 ppi is fine for web, projection and computer display. You only need higher ppi is you are printing and all you do is change it in the software at the printing stage.
I now await being corrected.
No images are 'taken' at any of these arbitrary resolutions (72 or 150). That is simply the resolution the images are being displayed at.
A camera records a given number of pixels on the x,y co-ordinates and therefore, if you look at the file from your friends camera and choose to display it at 72ppi, then it will look like a larger image file than if you choose to view it at 150 or 300 ppi
For example, my Nikon 3Ds has a resolution of 12 megapixels which means that roughly speaking there are 12,000,000 pixels on the sensor. These are distributed as 4256 x 2832 pixels. If I choose to display these at 72 pixels per inch, the resulting file would be very large but each 'inch' of displayed image would have less picture information than if I choose to display it with 300 pixels per inch (more densely packed, better image quality, smaller overall dimensions of the displayed image).
Monitors and the like have very poor resolution and therefore we do not need to have a high ppi number for the image to look adequate (hence 72ppi is use for web images). Print media is different and we generally accept anything between 240 and 300 being the optimum depending upon media in question.
As an aside, dpi and ppi are often used interchangeably. It's not strictly correct as one relates to print (dpi --> dots per inch) but it amounts to the same thing for our purposes
Hope that makes sense 
I think the PPI is added to the images when they are downloaded to the computer.
The images from the camera will always be the same amount of pixels as the sensor outputs. I know if you download direct to photoshop they will show at 300dpi, if you use software with the camera they may then show in at 72dpi.
The amount of pixels output from the camera will be the same no matter what the dpi is showing, as Barrie has said above.
For printing change to 300dpi, if you only look at screen then don't worry about it.
Quote: I think the PPI is added to the images when they are downloaded to the computer.
The images from the camera will always be the same amount of pixels as the sensor outputs. I know if you download direct to photoshop they will show at 300dpi
Only if that is what YOU have set Photoshop to display the images at.
As I say, the camera has no concept of ppi it is ALL down to the software you are using to view/edit the images at and that is generally tailorable by the user.
For example, Lightroom by default, outputs TIFFs from RAW files at 240 ppi. I chaged this so the files are output at the "industry standard" 300. Image dimensions (in inches/cm terms) are smaller but because the pixels are more densely packed, the image quality is better. I could have changed it to 437 if I so desired or any other number that I wanted 
The other thing to remember is that the ppi setting is irrelevant for displaying on screen. An image of a given pixel size will vary in display size according to the resolution of the monitor, not the image. i.e. if you are viewing a 1000x600px image it will fit onto a 1024x768 screen, but not on an 800x600.
Ian
Wow, some terrific responses here and thanks to all of you that have put your two pence bits in, it's always worth reading other peoples thoughts. Just to clarify a little - I took the files from the camera, copied them to the laptop, opened them in Photoshop CS and after doing a little jiggery pokery with more jiggery than pokery I noticed that the ppi size was 72. The image size was a massive 5184x3456 (compared to my 3008x2000 Nikon D100 file) so I resized at 300ppi to have them ready to print.
I told my friend that there must be a setting to have the ppi set to a better print size but was unable to find one. The Canon web site does not mention this ability and from some of the comments above the camera hasn't one.
When I resize to 300ppi the image size shoots up to a width of 21,600 pixels and a file size of 889.9M so I need to bring it back to a workable size (3000x2000 pixels).
As an aside Barrie, I have not set Photoshop to display images at any particular size but let it disply them from the original file it is opened in. That has always been the way I've done it because I've never been shown or told any different.
Hi Rob
You say you have resized to 300 dpi (ppi) but you have in fact 'up-rezzed' it and in doing so, made the file massive
As a suggestion, (there are other ways but this way you can see the effects of what you are doing), use the crop tool in Photoshop and clear the height and width boxes but set the resolution to 300. Then drag the crop tool from top left to bottom right so the entire image area is selected.. hit enter or click on the 'tick' at the top and your image will be resized to 300 dpi (ppi). If you have the rulers set on, you will see the image size change (which is why I suggested doing it this way )
For anyone who didn't know, when cropping in Photoshop, if you leave the height and width boxes clear, The crop tool becomes complete 'free format' - you can crop to any shape and it will set the image resolution to whatever is in the 'resolution' box. If you leave the resolution box clear, the resolution will be set according to a quick mathematical calculation based on the number of pixels in the area cropped
Does all that make sense
Brilliant Barrie
That crop tip will save me a donkey load of time. Now I have to convince my friend to buy a copy of Photoshop in order to get her pictures to a size suitable for printing without me.
Shame the EOS 550D doesn't produce images at 300ppi in the first place!
Quote:
Shame the EOS 550D doesn't produce images at 300ppi in the first place!
Glad that was helpful.
Just to pick up on your last sentence - you seem to have missed what I have been saying. The EOS 550D is the same as all other digital cameras in that the CAMERA has no need to have any knowledge of PPI. It does NOT produce a file with 'n' number of pixels per inch, it just produces a file containing a total of x megapixels. How these pixels are displayed on a monitor (i.e. when using viewing software or when using Photoshop or whatever) is purely a function of the software. Some by default display at 72ppi, others at 240pp and others at 300ppi and as the software user, you can generally change this to suit your needs
Best of luck
Add a Comment
ePHOTOzine, the web's friendliest photography community.
Upload photos, chat with photographers, win prizes and much more.
Login or Join Now
New to ePHOTOzine? Join ePHOTOzine for free!
Related Content
Join Our Free Newsletter
Awards
Current Competitions
foliopic 'Movement' Competition
1st May 2012 - 31st May 2012
This month's competition theme is 'Movement' which can be interpreted in a number of ways. You could photograph an animal running, a person walking or a car speeding...Featured e2 Photo
Featured Directory Listing
May's Photo Month
Check out ePHOTOzine's inspirational photo month calendar! Each day click on a window to unveil new photography tips, treats and techniques.
Interact
Photography Gallery Photography Forums Recent Forum Activity Members' Meetings Members' BlogsSearch ePHOTOzine
Having trouble or would like to make a suggestion? Create a report
Calibrate your monitor so you can see 16 different shades.
ePHOTOzine © 2001 - 2012 Magezine Publishing | Contact Us | Site Map | Top