Why wouldn't I shoot with the most pixels?

[Aidos107]

Hi all, I am new so please redirect me if this question has already been addressed.

I would just like to know what the benefit of shooting at 9 megapixels is, when my camera can shoot at 12?

The tutorials on this site have been very helpful and I have a better understanding of how sensors work, but I couldn't find anything on this topic. Do a quarter of the 'photosites' just turn off, orrr?

Also, if I'm going to view the pictures on a screen that is only 1920x1080, is there any point in shooting at 4000x3000? Would pictures be smaller and sharper, or just smaller?

If someone could explain what happens when you shoot at a lower than maximum image size, and why it is an option, that would be awesome.

Thanks,

Aiden

[loosecanon]

The only advantages are that the smaller file size will be written to your memory card quicker allowing more images before the buffer become full, and the images don't take up as much room on the card. As you have worked out the disadvantage is less image detail.

If you want say 4/3 rds images rather than the 3/2 image then it can save later cropping.In all cases you can never get back that which you don't record to the file.

In some cases a smaller file will be less prone to noise at high ISO or long exposure, simply because the signal from several pixels will be combined.

[James G]

Aiden, I'm not really up on the nitty gritty of how the technology works in detail, but my understanding is that it is not a sensor issue but a media issue.
By that I mean that the image is processed and resized in camera to the 'output' size you have selected and then transferred to your card.
The main reason for this is so that you can store more smaller images on your card without having to change cards or offload.

If you shoot raw, this is irrelevant since, keeping it very simple, the camera does no more than take what the sensor captures, and copies this to the card. You then decide how to process and size the raw image 'off camera' using either the proprietary software from the vendor or other 3rd party software that can read the raw format.
James

[Manfred M]

Hi Aiden and welcome to CiC.

It would be good to know what camera you are shooting with, as this might help put things in context a bit better, as the issue you are asking about can have multiple answers, and can be dependent on the camera / lens combination you are using or it can be as simple as the camera settings that you have dialed in.

Most of the users on this site shoot DSLRs, so I will try to answer in this context. In general, cameras do not use just part of the sensor, but rather use all of it and down-sample; i.e. use the camera’s image processor to create a smaller image. . Down-sampling means that some image data is thrown away to reduce file size, using something called “lossy compression”. The downside of this is that once the data has been thrown away, it is gone forever. The only exception to this is when one shoots a crop frame lens on a full frame sensor, where the camera only uses part of the sensor; pro and high end consumer cameras use larger sensors than consumer camera, so these consumer lenses are not designed to illuminate the entire full-frame sensor, so these images truly only use part of the sensor.

The main reason to use a smaller image is to save storage space; either on the camera’s memory card or on your computer. I generally shoot the best quality the camera is capable of, as both memory cards and computer storage are relatively inexpensive. On the other hand, in a real-life situation, if you are running out of storage space on your memory card and have no replacement available, you might want to do this so that you can keep shooting. After all, even reduced quality might be preferable to not have an image.

The question regarding image size (your 1920 x 1080 versus 4000 x 3000) example is fairly simple to answer as well. If you post to the internet straight out of the camera without doing any post-processing, then that image size is going to be fine, but it you ever want to produce a print or manipulate the image using post-processing software to crop or otherwise improve the shot, then your will want every pixel your camera is capable of capturing to give you maximum flexibility in post-processing work. From a print size, your 1920 x 1080 format is going to natively give you a postcard sized image, so if you want to print a larger format image, you are going to want to have those extra pixels.

[drjuice]

Hi, Aiden -

Before you make a decision to go small because you find your memory device is inadequate for some reason, I'd suggest looking for a larger memory device, using the same technology as you have now, but with more space. For example, when I got my DSLR, it came with a 2GB device. Since I already had an 8GB device, I put it into my DSLR. With the larger storage device, I was able to put all RAW images and their corresponding JPEGs from a day's worth of shooting (typically 200 separate images of each type) and not hit the limit of the 8GB device. However, I shortly did a shoot wherein I knew the 8GB device would probably not be enough, so I got a 16GB memory device. Except for shoots like the one I described just above, it is enough for a whole day. And, usually, it's good for 3-4 days of "regular" photography. The 16GB device was $18US + tax.
I still carry the 2GB and 8GB devices for those crunch situations. The only issue I ran into is that I had to get an adapter to plug the 16GB into my computer because my computer is so old that they only made 8GB devices back when I bought the computer. The adapter was $14US + tax. I'd suggest taking a look at online stores if you live in a smallish place.

One thing that I learned very early on, when I had a Canon Powershot back in 1991 (and before RAW was ever available, per se, that with digital imagery you want the most pixels you can get in the most easily converted format (RAW these days) because you never know when somebody will want an image of a particular person/object/animal/flower, etc. You can always make it smaller with many of the free apps available these days that allow you to resample the images. But, you can't reliably make it bigger without some significant software.

One of the best examples of this issue is that, in the El Dorado National Forest near Sacramento, I took some pictures of dandelions which had gone to seed. I entered one of them in a photo contest which required that the file not be bigger than the 1MB. Then, I got a request to give them the "original" for the magazine to use on its cover. So, I gave them the 38MB image (which was a technical challenge for them to get into their computer). So, I suggested that they tell me the usual size that they prefer working with for their cover. It turned out they normally get a 10-12MB file from the photographer. So, I had no problem producing that size file which turned out to work absolutely perfectly. That was the first and last time I believed the production people when they tell me "original" or 40MB or ....

I have some pictures that I took with my first 35mm camera and which I've scanned to 3500dpi and those usually come out to be something like about 10-12MB which is good enough for an 8.5x11 cover image or a full page on one of the internal pages.

I hope this helps you out.

virginia

[jcuknz]

Personally the only time I have shot at a lower resolution was when the person I was shooting for requested a smaller file to save them doing it when preparing the files for website use ....I always shoot at maximum resolution otherwise.
In one rare situation when I was runing out of storage I increased compression on the basis that personally I value resolution more than fidelity. But I have only had to do that once ... ever

There is an argument that you might get a 'shot of a lifetime' and how sad it would be if the camera was set at a lower setting and you couldn't benefit .... not sure I have ever captured a 'shot of a lifetime' ... YET