Final megapixel size of jpeg image?

<p>I thought I understood megapixel size, but having been away from digital editing for a while, my brain has fogged regarding what these numbers mean. Here is the info for a recently taken jpeg image taken with an older Olympus P&S camera. Let's say I wanted to explain the megapixel size of the image to someone. Here are the data I've retrieved. This may be asking a lot, but I'm sure this stuff is easy to decode, but I'm just getting confused.<br>

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<p >CAMERA: Older Olympus P & S: IMAGE taken as jpeg file</p>

<p > </p>

<p >Image opened in PS elements with the following information </p>

<p >2560W x 1920H</p>

<p >17.77 Width</p>

<p >13.33 Height</p>

<p >144 resolution</p>

<p > </p>

<p > Various data found on PS elements editor and in windows folder/file details for same image</p>

<p >PSE editor info lower left tab: 14.1 <strong >document size</strong></p>

<p >PSE editor info lower left tab: 171m/2.29g <strong >scratch size</strong></p>

<p >PSE editor (unedited save) 2.34 mg saved as <strong >jpeg</strong></p>

<p >PSE editorsaved ( <strong >as jpeg after adding ‘multiply’ layer</strong> and combining 2 layers, (i.e. orig. + mult. layer) 2.99 mg</p>

<p >PSE editorsaved edited image is 13.53 meg as <strong >PSD</strong></p>

<p ><strong >Windows library detail data of image 2354 kb }</strong></p>

<p ><strong >Windows library summary data of image 2.29mg } same as above?</strong></p>

<p ><strong > </strong></p>

<p >If you have the time, could you explain what these mean, and what would be the answer to the question, 'What is the megapixel size of your final image?<strong ><br /></strong></p>

<p>You are confusing Megapixel (MP) with Megabyte (MB). Megabyte is the size of the file in terms of storage or the amount of memory being allocated by Photoshop to edit the image. Megapixel is the number of pixels of the image in both the horizontal and vertical dimensions.</p>

<p>There is no such designation as "MG" in this environment.</p>

<p>The image above has the same megapixel value as it started with: 2560 x 1920 = 4915200 pixels or, for marketing purposes, 5 megapixels. </p>

<p>Right. Unless you're telling your editing software to lower the resolution of the image (making actual pixels go away), the final output in the JPG is going to involved just as many individual pixels (2560 x 1920) as you started with.<br /><br />The size of the FILE that records those pixels, in a JPG, is going to change based on how aggressively you tell the software to compress the image's details. Little or no compression means more visible details, but a more millions of bytes used to record those details. More aggressive compression will make the file smaller as it's stored by the computer (fewer millions of bytes), but also less visible detail, or some banding in gradient areas like the sky, etc.</p>

<p>Megapickles are a factor of resolution in pixel dimensions. Just multiply the pixel dimensions and there's your megapixels or, in the case of my old 3 and 4 mp digicams, meagerpickles.</p>

<p>File sizes are another critter. JPEGs are heavily compressed. When opened for editing they take up more space on disk. If converted to TIFF, PNG or other uncompressed file format, the file sizes will be commensurately larger.</p>

<p>If saving in layers, the file sizes will also be larger. More data, bigger files.</p>

<p>If you save a new version of the JPEG as a JPEG (naturally you don't want to actually replace your original JPEG), it may be significantly smaller or larger in file size depending on compression, even though the pixel dimensions (and megapickles) remain the same.</p>

<p>Dimensions in inches, millimeters, picas or any other linear dimension in the physical world are relevant only to printing. That gets into the often misunderstood issue of printing DPI/PPI. For editing purposes it doesn't matter whether the DPI/PPI is set to 72, 100, 250, 600 or eleventyseventy. It's only applicable to printing. The term "resolution" in that context is confusing because it's often mixed up with the same word applied to pixel dimensions/megapixels. Not the same thing. A 300 DPI "resolution" print from 4, 10 and 16 megapixel camera files will be different physical sizes, because the cameras have different resolutions. And if the prints from each were constrained to, say, 8"x10", then the DPI "resolution" would differ for each.</p>

<p>Clear as mud? The more I tried to explain this the worse I got. Someone else can probably do better.</p>

Megapixels? Simple. Multiply the height of the image x the width of the image , both as measured by pixels. In your case

2560x1920= 4,915,200 pixels or 4.9 megapixels.

2560W x 1920H

 

17.77 Width

 

13.33 Height

 

144 resolution

 

2560 times 1920 = 4,915,200 pixels = 4.9 megapixels. (What Ellis said.)

 

2560 pixels divided by144pixels per inch (PPI) = 17.77 inches

 

1920 pixels divided by 144 pixels per inch (PPI) = 13.33 inches

<p>A byte is eight bits. If you made a very simple 16-bit digital camera, it would need two 8-bit bytes to store the information from one 16-bit pixel. That should be clear, right?<br>

So, if that camera has 10 million pixels, a raw file would have to be at lest 20 million bytes in size, or 20 megabytes.</p>

<p>Now, the camera might store more information. It might store a small JPEG file, as well, to be used as a previous. It could store information about the camera, the lens, the time of what, preset settings, etc. So what's actually stored can get a bit complicated. </p>

<p>But our simple example shows that pixel and bytes are not the same thing, something that's a common misunderstanding.</p>

<p>One more concept: JPEG files use data compression. This is a mathematical algorithm that reduces the amount of storage needed to hold data. So, if you're talking about a JPEG file, it's not possible to determine how many pixels were used to create it. There's know way to accurately undo the compression that created the JPEG file.</p>

<p>Suffice to understand that pixels and bytes have very little to do with each other, and that there is often no way to find a correspondence between these two quantities.</p>

 

"<I>So, if you're talking about a JPEG file, it's not possible to determine how many pixels were used to create it. "</I><P>

 

??<P>

 

A 2560 x 1920 pixel wide by high RAW image saved as a JPEG at 80% compression is still going to be a 2560 x 1920 pixel wide by high JPEG image. The number of bytes used will reduce but not the number of pixels.