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DPChallenge Forums >> Tips, Tricks, and Q&A >> Megapixel size of image
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08/16/2020 12:15:15 PM · #1
I'm trying to upload an image to a canvas printer and the upload page says that the image must be less than 50 megapixels. I use Elements and when I click on image size, it sas "Pixel Dimensions 169.6M". Does that M signify megapixels?

If so, how do I lower that while retaining size? I can get it to 48.3 by taking the resolution to 160, but I don't want to do that, do I?

And... why the f*ck will these @$$holes let me upload the other one that's 118.3M???????

Yeah, I realize canvas doesn't need 300 dpi, but I've been getting them accepted before at 240.
08/16/2020 12:31:17 PM · #2
Well, I got it to 108.8M and they took it.....

I don't get how that's less than 50, but what do I know?
08/16/2020 12:36:46 PM · #3
You (or they) may be confusing megaPIXELs with the megaBYTEs of the file size as recorded to media -- the two are only loosely related. Multiply your image width x height in pixels to get the megapixel count (divide by one million).

How many megabytes it takes to record to media will vary widely depending on file format and compression method (if any).

Message edited by author 2020-08-16 12:38:27.
08/16/2020 04:32:02 PM · #4
MPís are simply L x W for the pixel count along the top and side divided by 1,000.000. They probably prefer to their own upsizing software rather than getting into quality arguments from folks who do their own (like I do).

Message edited by author 2020-08-16 16:32:39.
08/17/2020 03:06:43 PM · #5
Originally posted by GeneralE:

You (or they) may be confusing megaPIXELs with the megaBYTEs of the file size as recorded to media -- the two are only loosely related. Multiply your image width x height in pixels to get the megapixel count (divide by one million).

I'm not....the image sizing tool in Elements has the MB size in a different place entirely.
Originally posted by GeneralE:

How many megabytes it takes to record to media will vary widely depending on file format and compression method (if any).

Yeah, I know that, I'm trying to figure out the MP thing....

Thanks!

08/17/2020 03:35:08 PM · #6
Sure sounds like their website is stuck in the last decade decade before last... heck, there are multiple 35mm cameras that exceed the 50MP threshold for a single image these days! It seems like behind the scenes they are allowing larger images though, but you'd sure think they would bring things up to current standards!
And it's not like a pixel count > 50 MPx is unrealistic for a print either... a 48"x32" print at 240 dpi is 88.5 MPx. Upward of 10 years ago I had panoramas printed that met or exceeded that.
08/17/2020 03:58:25 PM · #7
I don't think you need as much as 240ppi for a canvas print, though I haven't actually checked on the native resolution of the printers those places use.
08/17/2020 04:02:11 PM · #8
Okay.... I truly don't know much about this stuff.

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What is the M for in the red blob?
08/17/2020 04:07:23 PM · #9
Originally posted by kirbic:

Sure sounds like their website is stuck in the last decade decade before last... heck, there are multiple 35mm cameras that exceed the 50MP threshold for a single image these days! It seems like behind the scenes they are allowing larger images though, but you'd sure think they would bring things up to current standards!
And it's not like a pixel count > 50 MPx is unrealistic for a print either... a 48"x32" print at 240 dpi is 88.5 MPx. Upward of 10 years ago I had panoramas printed that met or exceeded that.

I get so tangled up.....

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This file saved into Explorer says it's 14.2MB....that's megaBYTES, right?

If I open that 14.2 MB file in Elements, do nothing other than open the image size, Box 1 there is what it states.

So what is that 108.8?

Is that megabytes that shrink away when you save the file?

They were no help at the canvas place.

08/17/2020 04:21:37 PM · #10
That image is about 38 megaPIXELS ([5280x7200]/1000000) and takes up about 108 megaBYTES when stored in an uncompressed format.

ETA: the 14MB value incorporates some form of compression (probably JPEG) -- depending on image detail, color gamut and JPEG level it can compress anything from 10-90% (again megaBYTES, on disk -- nothing to do with pixels).

ETA more: in the "usual" color space(e.g. sRGB) each pixel takes 3 Bytes to describe (8-bits or 1 byte/RGB color), so your 38 megaPIXELS * 3 equals (approximately) 108 megaBYTES in an uncompressed format.

Message edited by author 2020-08-17 16:29:39.
08/17/2020 04:55:35 PM · #11
Originally posted by GeneralE:

That image is about 38 megaPIXELS ([5280x7200]/1000000) and takes up about 108 megaBYTES when stored in an uncompressed format.

Okay.
Originally posted by GeneralE:

ETA: the 14MB value incorporates some form of compression (probably JPEG) -- depending on image detail, color gamut and JPEG level it can compress anything from 10-90% (again megaBYTES, on disk -- nothing to do with pixels).

Okay. Does Elements uncompress it when you put it back into Elements? Because I put the 14.2MB file from Explorer into Elements to get a shot of Box 1....where it says it's 108.8M
Originally posted by GeneralE:

ETA more: in the "usual" color space(e.g. sRGB) each pixel takes 3 Bytes to describe (8-bits or 1 byte/RGB color), so your 38 megaPIXELS * 3 equals (approximately) 108 megaBYTES in an uncompressed format.

My brain hurts now...
08/17/2020 05:07:41 PM · #12
Yes, AFAIK all editing programs will uncompress the file when opened.

The fact that a 108MB file compresses to 14MB on disk means that the file has little fine detail, a limited color gamut, is over-compressed, or some combination of those factors (probably the last one).

Do not keep opening a JPEG and re-saving as JPEG -- you will lose a little quality each time. Save as TIFF or PSD (Photoshop, or whatever Elements uses as its native format) and do not save as JPEG until making your final output.

A TIFF saves with LZW compression (lossless -- preserves all data when uncompressed) should get that 108MB down to about 50MB; JPEG at best quality will probably get to to 25-35MB (just guessing).
08/17/2020 05:11:58 PM · #13
Originally posted by NikonJeb:

Originally posted by GeneralE:

ETA more: in the "usual" color space(e.g. sRGB) each pixel takes 3 Bytes to describe (8-bits or 1 byte/RGB color), so your 38 megaPIXELS * 3 equals (approximately) 108 megaBYTES in an uncompressed format.

My brain hurts now...

I use this amazing device called a digital calculator, even for simple arithmetic like this ...
08/17/2020 05:32:16 PM · #14
Originally posted by GeneralE:

I use this amazing device called a digital calculator, even for simple arithmetic like this ...

Smartass!

I never liked you! LOL!
08/17/2020 06:52:39 PM · #15
Maybe not as smart as you think ...

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08/17/2020 08:59:53 PM · #16
Originally posted by GeneralE:

Maybe not as smart as you think ...

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I think I just hurt something laughing!
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