Jpeg size vs. Sensor Mpixels: I shoot mainly with a Pentax K-50 which has a 16Mp crop sensor. My wife has recently been using a new Oly EM-10 111 which also has a 16 Mp sensor but, of...

mtcoothaman Loc: Brisbane, Queensland, Australia

I shoot mainly with a Pentax K-50 which has a 16Mp crop sensor. My wife has recently been using a new Oly EM-10 111 which also has a 16 Mp sensor but, of ourse, it is a m4/3.

I notice that her jpeg images average around 9 MP whereas mine for similar topics are about 7.5 MP. I would have thought that they would be similar. Can anyone explain this or is it due to the different manufacturers using different software or algorithms to convert from RAW to Jpeg?

(PS. I am impressed by the capability of the Olympus camera although, with my large hands, I feel it is a little small and some of the body fittings feels fragile , eg. the on/off switch and the battery hatch.)

bleirer

Question: are both cameras 14 bit sensors? That could be part of it, if one is 12 bit and the other 14 bit.

Wallen Loc: Middle Earth

JPEG is a lossy compression format. The final output size would depend on how much compression was done.

mtcoothaman Loc: Brisbane, Queensland, Australia

bleirer wrote:

Question: are both cameras 14 bit sensors? That could be part of it, if one is 12 bit and the other 14 bit.

Not sure. I will investigate.

Thanks

Notorious T.O.D. Loc: Harrisburg, North Carolina

The ISO can also impact the RAW file size which would then possibly impact the jpeg file size. Higher ISO yields larger RAW files with my Canon.

mtcoothaman wrote:

I shoot mainly with a Pentax K-50 which has a 16Mp... (show quote)

BebuLamar

JPEG are all 8 bit so the number of bits in the RAW file has no effect on the JPEG file size. The amount of compression and the amount of details in the image have effect on the JPEG file size. Noisier image has larger file size. A blank image would have very small file size. The M43 camera may have a bit more noise but I think the primary reason for the different in file size is the amount of compression.

DirtFarmer Loc: Escaped from the NYC area, back to MA

Jpeg compression can be a function of a compression parameter, which could easily be different for different camera models.

Also, the size after compression can vary significantly. A photo of a featureless surface can be compressed a lot. A photo with a lot of detail can only be compressed a little.

ygelman Loc: new -- North of Poughkeepsie!

bleirer wrote:

Question: are both cameras 14 bit sensors? That could be part of it, if one is 12 bit and the other 14 bit.

The number of pixels in an image depends on the image content.

To make a test, both cameras should try shooting the exact same scenes. . . with the same ISO.

bleirer

BebuLamar wrote:

JPEG are all 8 bit so the number of bits in the RAW file has no effect on the JPEG file size. The amount of compression and the amount of details in the image have effect on the JPEG file size. Noisier image has larger file size. A blank image would have very small file size. The M43 camera may have a bit more noise but I think the primary reason for the different in file size is the amount of compression.

I hear you, but the reason I'm wondering is that a 12 bit sensor captures 2^12 bits but a 14 bit sensor captures 2^14, when the camera demosaics and then runs the compression to jpeg, does if just throw away everything above 2^8, or does it squish It? I looked for a web resource but no luck, so now I don't know.

BebuLamar

bleirer wrote:

I hear you, but the reason I'm wondering is that a 12 bit sensor captures 2^10 bits but a 14 bit sensor captures 2^14, when the camera demosaics and then runs the compression to jpeg, does if just throw away everything above 2^8, or does it squish It? I looked for a web resource but no luck, so now I don't know.

It would remap the 14 or 12 bit to 8 bit before creating the JPEG.

NCMtnMan Loc: N. Fork New River, Ashe Co., NC

Some cameras let you adjust the compression of the jpeg files. Check them both to see if that is an option and it may answer your question.

ButchS Loc: Spokane, WA

mtcoothaman wrote:

I ... has a 16 Mp sensor but, of ourse, it is a m4/3.

I notice that her jpeg images average around 9 MP whereas mine for similar topics are about 7.5 MP. I would have thought that they would be similar. Can anyone explain this or is it due to the different manufacturers using different software or algorithms to convert from RAW to Jpeg?

You are confusing "megapixels" with "megabytes". Megapixels are a measurement of resolution. Megabytes is a measure of how much disk space the file takes up. Your photo is still 16 megapixels. But the JPEG file takes 7.5 megabytes of space on disk.

PHRubin Loc: Nashville TN USA

ygelman wrote:

The number of pixels in an image depends on the image content.

To make a test, both cameras should try shooting the exact same scenes. . . with the same ISO.

Yes - Image with a large area with little detail can be compressed more than one with great detail. In addition, the processor in the camera may be set for different amount of compression. This usually can be user selected, but even at the highest detail or file size setting, different cameras can be different.

mtcoothaman Loc: Brisbane, Queensland, Australia

ButchS wrote:

You are confusing "megapixels" with "megabytes". Megapixels are a measurement of resolution. Megabytes is a measure of how much disk space the file takes up. Your photo is still 16 megapixels. But the JPEG file takes 7.5 megabytes of space on disk.

My apologies re Mp and Mb-you are correct.

rehess Loc: South Bend, Indiana, USA

My K-30, which is like a K-50, allows me to control both the size-in-pixels and amount of compression for JPEG images. Most likely the difference is a small difference in compression {and the way they name them sometimes makes it hard to compare them}, but you need to compare all the JPEG parameters.
....

JPEG size parameter
JPEG size parameter...

JPEG compression parameter
JPEG compression parameter...