Picture size and quality

takinmore

Hi all, one thing that I am not at all sure of is whether there is any correlation between the size of a picture taken using raw processing and "quality".

Of course, I am not referring to whether the picture content is any good or has artistic merit, rather if my D70s (6mb) camera produces a photo of 7.2mb does that mean I captured every possible pixel and what if anything does that imply?

If I understand corrrectly, it allows for the best possible printing size right? But does it also imply that given that particular scene I captured as much detail as possible? Should I care?:dunno

my latest efforts are (I think) improving so that most pictures now come out at least 5mb and numerous ones are beginning to be around 6mb in size with the recent shot being 7mb. Is that good? Obviously from the technical and not artistic perspective.

Your thoughts and help would be appreciated as I am currently bewildered
(moderator - if this is the wrong forum I apologise - please move to correct place)

jfriend

There are a couple different things that influence a JPEG file size.

• The number of pixels you have captured.
• The compression level used when creating the JPEG

To capture and retain the best detail, you need to capture all the pixels that your camera can record. For JPEGs, this will typically be the highest resolution setting you have and is sometimes called "JPEG Fine". And, you need to use a low level of JPEG compression. "Low compression" means that less detail is thrown away in order to reduce the file size.

You cannot judge the amount of detail in a JPEG purely by it's file size because the effectiveness of JPEG compression is very much influenced by the subject matter in the photo. A night street scene where much of the image is black might compress to a very small size, yet still have recorded the maximum amount of detail for that exposure. Further, a lower resolution capture (recorded fewer pixels) or a scene with lots of detail in it at no JPEG compression might still result in a large file even though it doesn't contain nearly as much detail as it could if it were captured at full resolution.

To evaluate an image, you should first look at the actual pixel dimensions of the file (e.g. ~2000x3000 for a 6 megapixel camera or ~2848x4288 for a 12 megapixel camera). If those pixel dimensions are what you would expect for max resolution from your camera, then you are on the right track.

Then, you have to make sure that your camera is set up for a relative low amount of JPEG compression so that detail is not "compressed out" of the photo. You cannot easily judge this setting by only looking at the file size because the file size is a product of a number of different factors.

jeffreaux2

Capturing RAW will not net you any more pixels. The pixel dimension should be the same whether RAW or your highest jpg capture setting.

That said, I do recommend RAW capture as it provides you with all of the information from your sensor unadultered. I only shoot RAW. That is a whole other discussion though.

You may find this to be of interest....
http://dgrin.smugmug.com/gallery/2996921_HKMxn/1

takinmore

thanks to you both for the useful information. And apologies for my tardy response, I have been unable to spend time here lately.

I should have mentioned I always shoot raw (Nikon NEF) hence jpeg compression is mitigated. I can understand the resizing type issues that might impact resolution, I guess I am just unsure about whether I should care about the size of the raw image related to another.
For example, suppose I take a subject and photograph it twice using different setting (based onwhateer my particular desire for the image is. Let's say i use f8 for one and f11 the other with Aperature priority so the speed will be different. I later look at each picture and see one is close to 6Mb and the other 5Mb. Artistic needs aside, is the bigger one the best amount of data to work with in post? in other words, did I get more pixels out the the larger picture? Or does it matter? (or does any of this make sense?)

thanks again for any help

jfriend

takinmore wrote:

thanks to you both for the useful information. And apologies for my tardy response, I have been unable to spend time here lately.

I should have mentioned I always shoot raw (Nikon NEF) hence jpeg compression is mitigated. I can understand the resizing type issues that might impact resolution, I guess I am just unsure about whether I should care about the size of the raw image related to another.
For example, suppose I take a subject and photograph it twice using different setting (based onwhateer my particular desire for the image is. Let's say i use f8 for one and f11 the other with Aperature priority so the speed will be different. I later look at each picture and see one is close to 6Mb and the other 5Mb. Artistic needs aside, is the bigger one the best amount of data to work with in post? in other words, did I get more pixels out the the larger picture? Or does it matter? (or does any of this make sense?<S>)

thanks again for any help

If you're shooting RAW, all your images are the same number of pixels. Many cameras offer a form of lossless compression for RAW and the effectiveness of the compression will vary from one image to the next, but that doesn't have anything to do with image quality, just how easy the image is to compress. So, the answer to your question is NO. You can't tell anything about the quality of a RAW image from it's filesize.

jeffreaux2

The file size in MB will vary depending on the amount of fine detail in a photograph....even if all are shot in the same format and quality. Another way the file size will change is to discard the color information.....that is....convert a file to a black and white.

Ive had RAW files vary in size from my 50D Canon from 12MB all the way up to 25MB....even though I always capture in RAW (large).

takinmore

thanks again everyone - so it is the amount of detail in the picture that applies if the file size grows. I know it is not always the same since my D70s often gives me anywhere between 4 and 6.5Mb in file size and the camera's "pixel size"is 6Mb. I appreciate everyone taking the time to answer

ziggy53

takinmore wrote:

thanks again everyone - so it is the amount of detail in the picture that applies if the file size grows. I know it is not always the same since my D70s often gives me anywhere between 4 and 6.5Mb in file size and the camera's "pixel size"is 6Mb. I appreciate everyone taking the time to answer

Unfortunately, noise is treated like (and competes with) image detail even by lossless data compression. A high ISO image of the same scene as a low ISO of the scene will often be larger in file size. Unfortunately too, extra detail doesn't necessarily mean more detail in areas "you" are interested in.

Your Nikon D70s is rated at around 6 mega-"Pixels", not 6 mega-Bytes. It is often abbreviated as 6MP or 6MPix.

As has already been said, do not use file size as a measure of image detail except in very carefully controlled circumstances with "very" similar images, shot with the same exposure settings. If I'm locked down on a tripod and I take several images of the same scene with manual focus, I may use file size to hint at which scene has the most detail, but I always confirm with a visual inspection.

takinmore

thanks Ziggy! That helps a lot. I hadn't thought of noise being a variable, but of course it makes good sense. I'll generally ignore size unless the pictures are really closely related and with the same ISO, aperature and speed.

Thanks