Trying to understand pixel counts

[Grandpa Ron]

My Canon T6 Rebel DSLR advertises 18 Mega pixels. However, when I view the photos they are usually between 5 Mega-pixels and 10 Mega-pixels.

Here are two similar photos,

This one is 7.54 Mega-pixels.



This one is 10.0 mega-pixels.


They were both shot on the Auto setting producing a JPEG format. Naturally for posting purposes I reduce them to 1000 pixels on the long side.

So, my question is why is the camera not using all the 18 mega-pixel I paid for?

 

[480sparky]

Are you reading mp, or file size in mb? EXIF data shows the "10.0mp" image to be 5184 x 3456 pixels, which is 17,915,904 pixels. Close enough to be 18mp.

 

[AlanKlein]

The sensor has 18mb in pixels. But then the camera reduces the image size by compression when it creates the jpeg image. Your camera probably has different settings for jpeg images such as small, medium, large and maximum. Each of them will provide an image with a resolution of 5184 x 3456 pixels, which is 17,915,904 pixels. However, when it's converted by the camera into a jpeg, different compression algorithms are used. I always keep it at minimum compression which means maximum size to prevent banding and other artifacts that can occur with jpegs, especially when you enlarge them and it's easier to see the artifacts and banding. You should consider compression selection as well when you edit your picture and then create new jpegs of the edited picture. Check what's recommended by the software editing manual.

Note that at the same compression setting, you will see different total MB as compression works differently depending on what's in the picture. For example, a big sky with lots of blue compresses more. Look up jpeg on the web for a detailed explanation.

 

[AlanKlein]

Besides compression, your camera probably has image size. That relates to resolution. So instead of 5184 x 3456 pixels, which is 17,915,904 pixels, you can select smaller sizes of resolution such as 3000 x 2000, 1500 x 1000 or 600 x 400 pixels. These could be handy if you only want a smaller size for emailing or posting on the web. But keep in mind, once you get a smaller picture, if you need a larger one with more pixels, you can't reverse the process and create a large picture with maximum resolution. I always shoot with maximum resolution and then reduce when editing and creating a second image at a smaller size.

Some cameras also can store RAW plus jpeg where you get two images to work with afterward. Some cameras also store a single smaller still picture at the beginning of a video clip. Check your manual.

 

[LWW]

The megaPIXEL count of 18mp is accurate.

The image is stored in a JPEG file which compresses the file. Hence the megaBYTE storage and the 10mb storage is also correct.

When the file is compressed some details data is binned to transfer/save/load faster ... the downside being it suffers a bit of a loss in quality.

Depending on enlargement size desired, this may not be a big deal. IOW a web resolution from a jpeg is fine. a 60 X 40 not so much.

Stored without compression, say a TIFF file, will maintain all the data but at a much slower transfer/save/load time. Again, maybe or maybe not a big deal.

If you are shooting a lamdscape from a tripod, EZPZ. If you are shooting sports and want the highest frame rate possible ... this can feel like slogging through the mud with my brother on my back at times ... especially with an older card and/or DSLR.

I shoot nearly everything in RAW and correct in post ... except for snapshots.

I hope this helps.

 

[Grandpa Ron]

Once again I was foiled by not paying attention to details. I should have noticed Megabytes vs Megapixels.

It is interesting to know that JPEG compression varies with the subject matter. I have noticed that the more times a photo is copied and pasted, there seems to be a loss of detail.

Thanks for the info.

 

[LWW]

Once again I was foiled by not paying attention to details. I should have noticed Megabytes vs Megapixels.

It is interesting to know that JPEG compression varies with the subject matter. I have noticed that the more times a photo is copied and pasted, there seems to be a loss of detail.

Thanks for the info.

Life is a learning experience Ron.

Internet forums allow us all to deposit into the the cosmic consciousness, and withdraw data as needed.

Glad I could be of assistance.

BTW, on a jpeg format you can open and close it countless times without loss, but each time the file is alteeed it undergoes compression again adding to the lost data.reds