Photo files 101: All about megapixels, megabytes, and DPI

#1 Macworld

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Posted 17 July 2012 - 05:01 AM

Post your comments for Photo files 101: All about megapixels, megabytes, and DPI here

#2 bastion

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Posted 17 July 2012 - 06:25 AM

Another wrinkle. Almost all digital cameras only actually capture one color component (R, G or

per pixel. The other values are interpolated based on the surrounding data. The pattern of the captured components and the quality of the interpolation will also affect image quality.

#3 chrisb63

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Posted 17 July 2012 - 06:27 AM

Thanks a lot for this !!
Now, what settings should I use in Lightroom for exporting my pics to viewed on the retina iPad ?
size 2* 2048-1536, twice to allow zooming
and 264 ppi ?
Is that correct

#4 monospaced

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Posted 17 July 2012 - 07:00 AM

chrisb63, on 17 July 2012 - 06:27 AM, said:

Thanks a lot for this !!
Now, what settings should I use in Lightroom for exporting my pics to viewed on the retina iPad ?
size 2* 2048-1536, twice to allow zooming
and 264 ppi ?
Is that correct

Export @ 2048x2048 pixels (or higher, to allow zooming as you say). Resolution is irrelevant on-screen. It could be 1ppi or 2048ppi.

This post has been edited by monospaced: 17 July 2012 - 07:01 AM

#5 chrisb63

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Posted 17 July 2012 - 07:14 AM

monospaced, on 17 July 2012 - 07:00 AM, said:

chrisb63, on 17 July 2012 - 06:27 AM, said:

Thanks a lot for this !!
Now, what settings should I use in Lightroom for exporting my pics to viewed on the retina iPad ?
size 2* 2048-1536, twice to allow zooming
and 264 ppi ?
Is that correct

Export @ 2048x2048 pixels (or higher, to allow zooming as you say). Resolution is irrelevant on-screen. It could be 1ppi or 2048ppi.

#6 chrisb63

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Posted 17 July 2012 - 07:21 AM

@ monospaced
That's where I get lost.
Why resolution is irrelevant ?

#7 Stewsburntmonkey

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Posted 17 July 2012 - 07:34 AM

chrisb63, on 17 July 2012 - 07:21 AM, said:

@ monospaced
That's where I get lost.
Why resolution is irrelevant ?

Resolution here is referring the DPI. Virtually all digital displays ignore the image file's specified DPI and either display a scaled version or display the image with one image pixel per display pixel. I would suggest not messing with the DPI of image files in most cases as it can cause some issues with photo editing software (image files can end up being saved several times larger than desired).

This post has been edited by Stewsburntmonkey: 17 July 2012 - 07:35 AM

#8 bjmac

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Posted 18 July 2012 - 05:34 PM

Your picture above of saving a copy of a photo reminded me how Apple, for some unfortunate reason, removed the actual file size information from the latest version of Preview in Lion. This leaves the user in the frustrating position of having to guess what the reduced file size will be - and if it isn't what they had hoped for, having to resize it again and again. I can't comprehend why they would do such a thing.

#9 Banksia

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Posted 18 July 2012 - 09:16 PM

Cameras with quality lenses can often produce MUCH BETTER images with a smaller megapixel count than a camera with a fair lens and lots of megapixels. Glass does matter.

#10 bastion

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Posted 19 July 2012 - 04:42 AM

bjmac, on 18 July 2012 - 05:34 PM, said:

Perhaps too many people complained that Preview's guesses - and that's what they were - were wrong.

Honestly, I hadn't even noticed this omission myself because file size, to me, is much less important than image dimensions and quality.