Megapixels and Resolution

[laawaaris]

When you save a JPEG file right out of the camera as JPEG 10 in Adobe Bridge/Photoshop - does it result in a loss of resolution?

When I take the JPEG file out of my D200 camera it is about 3 MB in size. However when I take this file into Adobe Camera Raw and correct the exposure and save it, the resulting file is now about 1.5-1.7 MB.

I had a customer complain that the files I gave him are not high resolution. He said that the files were only 1.7 MB in size and that does not match what a 10 Megapixel camera can produce. He was also complaining that when he put the photos as a screen saver on his computer, he could see pixels and squares as an indication that it was not high resolution.

I am not an expert on resolution and was not able to clearly understand the problem - so I am turning to the forum for some guidance.

All I know is that I always save my D200 files as JPEG 10 and have had no real problems. I have been able to blow up to 20x30 without any noticeable problems.

Please do let me know if there are any details I should be aware of.

[LanceHaynie]

What resolution did you set them at?

My guess is when you saved them they were at 72 pixels per inch. For prints I save all my JPEG's at 300ppi, resulting in an 11x14 cropped image around 4megs.

In photoshop, open one of your jpegs and go to Image -> Image size and see what the resolution says.

Hope that helps!

[laawaaris]

Sorry I left out the vital piece of information ... I save everything as 300 DPI.

I just tried it as a test, opened ACR and set the resolution to 300, and the JPEG quality to 10

When I saved the image via ACR the original 3.35 MB file was trimmed down to 1.71 MB

[LanceHaynie]

Originally Posted by laawaaris

Sorry I left out the vital piece of information ... I save everything as 300 DPI.

I just tried it as a test, opened ACR and set the resolution to 300, and the JPEG quality to 10

When I saved the image via ACR the original 3.35 MB file was trimmed down to 1.71 MB

With that being said I have no clue then. I shoot in RAW and those files do go down in size, but my guess would be because of metadata that doesn't translate.

My avatar shot was a 5.10MB file in Nikon Raw (NEF) and the JPEG went to 2.93MB.

I am shooting a 6mp camera though so your 10mp should be producing higher quality. My guess is if you have printed larger prints no problem in the past, its your guys issue. What resolution (pixels width and height) is the JPEG?

[LoungeLizard]

What are the results if you save at level 12? I bet that the additional compression is the cause.

From a quality point of view, there is nearly no difference between level 10 and level 12. I save everything at level 10 - files are nearly half the size.

[laawaaris]

Yeah I am really confused. My concern is that if it is a problem with this one client - then I want to be able to have a better understanding for the next client.

My files are shot at the JPEG "Large Fine" setting in my camera - which results in a 2592x3872 image - or a 10.04 Megapixel file.

This file is usually around 3.5 MB in size and has never been larger than 4 MB from my D200.

I do know that my JPEG files always reduce in size if I save them as JPEG quality 10. If I save them as JPEG quality 12, they will increase in size.

I am pretty convinced that the JPEG quality 10 file that I save to disk after editing is still a 10 Megapixel image. However, the client is not convinced due to the fact the file size is only 1.7 MB - and so I am a little lost at to the technical details about the imaging and resolution involved.

[LanceHaynie]

Originally Posted by laawaaris

I am pretty convinced that the JPEG quality 10 file that I save to disk after editing is still a 10 Megapixel image. However, the client is not convinced due to the fact the file size is only 1.7 MB - and so I am a little lost at to the technical details about the imaging and resolution involved.

Well size doesn't really correlate to megapixels, the JPEG setting is your compression ratio, so you can compress an image and still be a 10mp image.

The megapixel math is actually quite easy, but I dont know that it helps you here. You take the height and width (2592x3872) and do it like a math equation to get 10,036,224 since megapixels are in millions, that means that image is 10.036 megapixels no matter what. So you are right, it is still a 10mp image.

[rdcole]

The squares your client was seeing are a result of the JPEG compression.
JPEG is a Lossy compression system so it throws away information the algorithm thinks the human eye will not see. As a result each time and image is saved some image quality is lost how much is dependent on the quality level used during the save. This is information you can't get back.

Try an experiment, save the same file at various quality settings, you will a huge difference in the file size with quality settings of 12 down to say 3.
When you open a JPEG quality 3 file its still 10 mega pixel photo but it will not look very good because the compression algorithm has thrown out so much information.

If the client wants larger files give them JPEG quality 12 or TIF files.

[LoungeLizard]

Originally Posted by rdcole

The squares your client was seeing are a result of the JPEG compression.
JPEG is a Lossy compression system so it throws away information the algorithm thinks the human eye will not see. As a result each time and image is saved some image quality is lost how much is dependent on the quality level used during the save. This is information you can't get back.

Try an experiment, save the same file at various quality settings, you will a huge difference in the file size with quality settings of 12 down to say 3.
When you open a JPEG quality 3 file its still 10 mega pixel photo but it will not look very good because the compression algorithm has thrown out so much information.

If the client wants larger files give them JPEG quality 12 or TIF files.

Just be careful with this logic. Saving a file at a lower quality level will result in loss of data. Saving the file at the same quality level will not affect quality - that is a misconception. Of course, once the information is gone, there's no way to get it back.

Lance is right. Do the math - and teach your client to do the math!

[laawaaris]

I did explain to my client that JPEGs were compressed - which is why they file size seemed smaller.

The client then asked me how to reverse the compression - I feel he needs to see a larger file size in order to feel satisfied.

If he opens the compress (level 10) JPEG in photoshop and then saves it as Level 12, the file size will go up. Is this a "lossless" way to reverse the compression?

Essentially once you have a baseline JPEG, can you freely and openly save at any level from 1-12 and not lose information each time you are saving?

[laawaaris]

Ok thanks everyone for the information.

The only puzzling point is why the files I gave him are showing squares - level 10 is compressed but not that much - and I would not save my files in Level 10 if I myself saw squares and pixels !

[LoungeLizard]

Originally Posted by laawaaris

If he opens the compress (level 10) JPEG in photoshop and then saves it as Level 12, the file size will go up. Is this a "lossless" way to reverse the compression?

Nope. Once the data is thrown out, it's gone. PS has just "extrapolated" to the best of it's ability and guessed what data may have been there.

Only thing you can do is go back and resave the images from the original out of camera files at level 12.

[Duffy Pratt]

My guess is that your client is seeing things that aren't there. He sees a smaller file size, and as a result expects a loss of quality. Thus, he's seeing a loss of quality.

If you want to test this, send him the picture again, but this time convert it first to a 16 bit tiff. It won't have any more information, but it will be a much bigger file. See if he thinks its better.

Duffy

[jeffkohn]

Originally Posted by laawaaris

Ok thanks everyone for the information.

The only puzzling point is why the files I gave him are showing squares - level 10 is compressed but not that much - and I would not save my files in Level 10 if I myself saw squares and pixels !

If he is seeing pixellation from 10mp JPEG's saved at quality=10, the most likely culprit is his screen saver doing a poor job of resamplling the image down for display on screen.

[laawaaris]

thanks for the information jeff and everyone

i've learned a lot about resolution and imaging technicals from this discussion ... i've made some notes as a reference to solidify the knowledge ...