How can I check the resolution of an image?

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BertieTBE

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Hello.

Bit confused about this...

What's the best way to check the resolution of an image? I'm most interested in what happens once they are printed.

I've been asked to supply high-resolution images (at least 200 DPI), which would be printed. All the images I have on my computer are 72 DPI (according to Preview). Can't work out how to check this in Lightroom.

I've tried using the largest JPEG setting, and RAW format on my Canon 600d. Both are coming out as 72 DPI. It also says teh file size 6mb which doesn't bode well!

I just want to ensure they would look ok if they ever needed to be printed in a larger size.

Any advice much appreciated.

Thank you.

BertieTBE
 
Last edited:
BertieTBE said:
Both are coming out as 72 DPI.
Click to expand...

As long as there's no print, there are also no dots per inch. A digital picture doesn't have a size measured in inch. Just deliver with the highest resolution you have. From that you may calculate the maximum size of the print regarding to the requested dpi.
 
Size of intended print (in inches) divided by the pixel dimensions of the image.

If you don't know the printed size you can't calculate it. Expect whoever is asking you about the image not to understand this.
 
Other way round.

Since I know my old D70 produces (as near as damn it) 3000 pixels x 2000 pixels, I'll use that as my source. If I want a print from it at (conveniently!) 30" x 20", I'll get a resolution of 100 DPI, at 15" x 10", 200 DPI.

So, take your sensor's output size in pixels (you'll find that in the manual or online) and divide it by the final print size (which the person/company you're giving the file should be able to tell you. That'll give you the resolution. OR, take the pixel size and divide it by their required resolution (200 DPI) and that'll tell you how big the prints can be.

If your camera can't provide enough resolution, it is possible to enlarge the pixel dimensions of the file but you won't get any extra detail. Most PP software can do this but IIRC, some do it better than others.
 
enlargement would only add pixels artificialy based on adiacent ones. the camera may have settings for higher quality jpegs or shoot raw and then process the image. you can use preview tools menu to change file resolution.
 
cristianr said:
enlargement would only add pixels artificialy based on adiacent ones.
Click to expand...

Already mentioned, some software will do better than other. The one who does the print, especially if it's done by a professional, may have a better working software. So check, before you increase the resolution by yourself!
 
Bertie, 'resolution' only matters for output to print. Whenever you look at images on your computer it automatically shows them at 72ppi or 96ppi or similar, depending on your monitor resolution. What the requestor is asking for is a large file size. If your camera has at least 8mp then taking images at that file size will be sufficient as long as you don't crop enormously. Save your file as a high quality jpg and check the image dimensions in pixels - e.g. 2000 x 3000 = 6mp. If you end up with a figure less than 1mp its probably not sufficient. Do not try to upsize an image. Its rarely successful.
 
Your camera's sensor outputs an image size of 5184x3456, that's a print of over 17" x 11" So roughly an A3 print at 300dpi.
Just for clarity, an A3 print only needs to be about 200 dpi as the human eye can't resolve 300dpi at a comfortable viewing distance for an A3 print. I hope that's not too confusing.

Basically, your 600d could produce a 10 foot wide print and it'd look fine from the viewing distance required for a print that size.
 
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