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Author Topic: Canon 700d or any DSLR- Pixel size/ Document Size  (Read 1075 times)
littleillustrator
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« on: May 22, 2014, 11:48:53 PM »
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Hello,

I am just looking to get an entry level DSLR and looking at the Canon 700d, the thing I don't quite understand is the pixels.

I need a camera that will allow me to print images at 300 dpi on a fine art printer at roughly A3 size (11.693 x 16.5"). I am a digital illustrator and I tend to scan things in at high res 1200dpi, but I want a DSL camera that will allow me take photos of textures or items in different positions and distances, which you can't do with a scanner. Thus a new camera.

But I don't quite understand the pixel sizes, it says large 17.9 megapixels (5184x3456) but how do I exactly work out what that will equate to with dpi? Like I know my old lumix, came in at a certain pixel size and the dpi was 180

So does that mean the document size at 300 dpi will be 43.89x29.26 cm (17.2 x11") ?


Is this how I figure out what the document size for cameras I am interested in looking at

Thanks

« Last Edit: May 22, 2014, 11:52:15 PM by littleillustrator » Logged
Hening Bettermann
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« Reply #1 on: May 23, 2014, 05:05:41 PM »
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Bart van der Wolf has given us a tool, part 1. of which, I believe, will answer your questions:

http://bvdwolf.home.xs4all.nl/main/foto/dofplan/dofplan.html

Good light!
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BradSmith
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« Reply #2 on: May 23, 2014, 08:41:04 PM »
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I suggest you think of image size that any camera produces as being a rectangle that is so many pixels long by so many pixels wide.  In the case of the camera you mentioned, that sensor would capture an image file with the dimensions of 5184 pixels long by 3456 pixels wide.   Now to print size.   You don't have a print size until you tell your software what pixel resolution (pixels per inch or cm) to apply to the pixel dimensions of your camera's capture or cropped image.  For example, you tell your software to print the image at a resolution of say, 100 pixels per inch.  In order to figure out how large that image will print, you'd:  divide 5184 pixels by 100 pixels per inch and you'd end up with a printed image that was 51.84 inches long, and; 3456/100 = 34.56 inches wide.  That is what the software is doing in the screen shot that you showed, except in that case the pixels per inch resolution figure that you entered was 300 pixels per inch, thereby resulting in the 17.2 x 11 inch print.

Note that the "Resample Image" box at the bottom of the Image Size screen you included is unchecked.  This is important for what I'm explaining, which is print size without resampling to create more or fewer pixels in your image.  In the example you presented, you are working with the original number of pixels that your camera captured.  Resampling is a longer discussion that I won't go into. 

Hope this helps
Brad

Brad
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littleillustrator
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« Reply #3 on: May 23, 2014, 09:29:19 PM »
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@ Hening- Wow what a great resource, but a bit complex at this stage for me. I am sure I will use it when I get my head around photography a bit more. But I get you what will it look like at viewing distances.

@brad - thanks, that makes sense to me.

I am interested to know what the dpi is set to for cameras. For example when I open up a photo from my lumix it has 180 dpi.

So that means my image size has to go down if I want it at 300 dpi

If the canon image was was 5184x3456 at 180 dpi that would mean I would have to reduce image size to get dpi up.
« Last Edit: May 23, 2014, 09:37:03 PM by littleillustrator » Logged
MrSmith
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« Reply #4 on: May 24, 2014, 02:30:34 AM »
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You almost have to stop thinking about the DPI. Photographers get asked about file size all the time and whenever they reply "it's 36 megapixels" or "it's a 120mb tiff" the response is often "yes but it has to be 300dpi for repro".

I could supply an iPhone pic at 300dpi and it would not be big enough for the clients needs, I could also supply a stitched tiff file of over 400mb and it would be rejected for being 180dpi.

If the image size is not re-sampled for printing then more megapixels and bigger pixel dimensions mean bigger prints whatever the dpi of the file.
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ErikKaffehr
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« Reply #5 on: May 24, 2014, 02:41:44 AM »
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Hi,

The DPI is just a tag value, which is meaningless, really. What I would add is that is always best to print at a multiple of the printer resolution. For Epsons that would be 360 or 720 PPI, Canon printers may work best at 300 or 600 PPI. The reason is taht you can do better interpolation in Photoshop than what is done in the printer driver.

The way you try to find out resultion is quite OK, but the simplest is just to multiply PPI with image dimensions and check resolutions.

Best regards
Erik
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Slobodan Blagojevic
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« Reply #6 on: May 24, 2014, 08:02:33 AM »
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If photographers are to become extinct one day, it might be because of a collective suicide, after being asked one too many times to "just deliver files at 300dpi."

It is like being told "Please take a car and deliver this file to a client. Where to? Do not worry where, just drive at 55 mph."
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Slobodan

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Slobodan Blagojevic
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« Reply #7 on: May 24, 2014, 01:38:06 PM »
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... I am interested to know what the dpi is set to for cameras. For example when I open up a photo from my lumix it has 180 dpi.

So that means my image size has to go down if I want it at 300 dpi

If the canon image was was 5184x3456 at 180 dpi that would mean I would have to reduce image size to get dpi up.


1. Let's just start with a simple fact: the only thing that is set for cameras is the file dimension in pixels, or, in your case, 5184x3456. Everything else is a calculated value based on that, like dpi. You can not say that a particular dpi is "set" for cameras, just as you can not say that a particular miles per hour (say 55mph) is set for cars. You can not thus say that your Lumix "has" 180 dpi.

To calculate dpi, you need two other elements: file size in pixels and print size in inches. Like in any math formula, when you have two elements, you can always calculate the third.

I suspect that, when you open your Lumix file and it "has" 180 dpi, you actually had previously set that value in software preferences (or the software manufacturer already set it for your convenience). It is an arbitrary number, and can be any other (like 72, 96, 240, 300 etc.) just as well. It is, however, a reasonably well chosen number, as it corresponds with a minimum dpi necessary for high quality printing on glossy media. The reason a number like this exists in the Resolution field in Document/Image Size is to give you a starting point and an idea how big you can print with a reasonable quality. In absence of any number in the Resolution field, the other two fields (Width and Height) would also be empty.

2. If the Resolution field says "180," and you want to go to 300 dpi, your image size is NOT going to go down (it will always remain the same, as 5184x3456). What is going to go down is your print size.

So, to answer your OP question, if you want to print to approximately 11.7" x 16.5" and you want it to be at 300 dpi, your camera should be able to deliver the file with 4950 x 3510 px. So, a camera with 5184 x 3456 px would be sufficient.
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Slobodan

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