Question on Image Size affect on sensor: I am curious how the sensor works when I choose a smaller size. For instance, my camera is capable of shooting 24MP. If I set the size to 6MP...

photon56 Loc: North America

I am curious how the sensor works when I choose a smaller size. For instance, my camera is capable of shooting 24MP. If I set the size to 6MP (small), does the sensor turn off pixels or does it remove them during the save process to the memory card?

amehta Loc: Boston

photon56 wrote:

I am curious how the sensor works when I choose a smaller size. For instance, my camera is capable of shooting 24MP. If I set the size to 6MP (small), does the sensor turn off pixels or does it remove them during the save process to the memory card?

My semi-educated guess is that no pixels are turned off, at some point in the processing the extra pixels are thrown out.

I am curious why you ask?

photon56 Loc: North America

amehta wrote:

My semi-educated guess is that no pixels are turned off, at some point in the processing the extra pixels are thrown out.

I am curious why you ask?

It's my technical side of me likes to know how it works. If it throws out pixels, how does it decide which ones? Depending on the answer might help my decision of when to use the setting and the true expected results.

amehta Loc: Boston

photon56 wrote:

It's my technical side of me likes to know how it works. If it throws out pixels, how does it decide which ones? Depending on the answer might help my decision of when to use the setting and the true expected results.

Yes, I understand the technical side wanting to know how it works. :-)

I don't think it is the best way to reduce the image resolution, because I do believe it throws away pixels. Other methods which use algorithms to "average" adjacent pixels should give better image quality, mainly because noise will get averaged out. If the camera throws out pixels, the resulting image is as bad as what you see when you look at a image at 100% magnification.

photon56 Loc: North America

So, from what you're saying, using 6mp on a 24mp camera could look worse than a 6mp photo taken on a 6mp camera.

zundapp5 Loc: Portugal

photon56 wrote:

I am curious how the sensor works when I choose a smaller size. For instance, my camera is capable of shooting 24MP. If I set the size to 6MP (small), does the sensor turn off pixels or does it remove them during the save process to the memory card?

All pixels are used, and then, the image is down-sampled by the camera software... I believe!

John N Loc: HP14 3QF Stokenchurch, UK

I had a feeling that the camera selects pixels at random when not using the full sensor capabilities and that the picture is recompiled from this info when the image is downloaded.

kymarto Loc: Portland OR and Milan Italy

There are different algorithms for upsampling or downsampling: pixels can be thrown away or adjacent pixels interpolated in varying ways. I have no idea what your particular camera does.

dcampbell52 Loc: Clearwater Fl

zundapp5 wrote:

All pixels are used, and then, the image is down-sampled by the camera software... I believe!

You are exactly right. All cameras shoot in raw then convert to .jpg .tiff or whatever (yes even point and shoots) The process is automatic. The DSLR and some mirror cams allow you to keep the raw file and the .jpg. or one or the other. Raw is always the max resolution (with a few exceptions, like the ability to shoot in cropped mode), and the camera down converts to .jpg fine, normal or whatever then throws out the raw to save space.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Crop mode on Nikon FX cameras use only the crop area, discarding all pixels outside the crop. It is how they achieve a faster frame rate and smaller image size. If the camera had to capture the full sensor's worth of data, then process the image to "crop" it, the camera would be slower, not faster, though the buffer would take longer to fill.

dcampbell52 Loc: Clearwater Fl

Gene51 wrote:

Crop mode on Nikon FX cameras use only the crop area, discarding all pixels outside the crop. It is how they achieve a faster frame rate and smaller image size. If the camera had to capture the full sensor's worth of data, then process the image to "crop" it, the camera would be slower, not faster, though the buffer would take longer to fill.

exactly, that's why I listed it as an exception.

HarryBinNC Loc: Blue Ridge Mtns, No.Carolina, USA

My Nikons create downsampled jpgs - the small ones are 1/4 the Mpxls of the large ones - for my D800, that means the Small is 9 Mpxls instead of 36. The linear dimensions (print size)are halved, so instead of getting a 16 x 24" print at full size, the small size results in a 8 x 12" print at 300 dpi. The accompanying RAW files are full size in both cases. The medium setting gives 20 Mpxl jpgs, which would print at 12 x 18 (300dpi). These are all jpg Fine, so all would result in equally high quality prints at their 300dpi print sizes.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

HarryBinNC wrote:

My Nikons create downsampled jpgs - the small ones... (show quote)

You must have special Nikons. The manual is quite clear - the cropped modes are not downsampled, they use the center of the sensor. It is not a full-sensor image that processed to a smaller size.

This is explained on pages 80-82 in the D800 manual. Also, when you use crop modes af sensors fill more of the image, so in the smallest crop mode, the entire area is filled with sensors. This would not be possible if the image was downsampled.

dcampbell52 Loc: Clearwater Fl

Gene51 wrote:

You must have special Nikons. The manual is quite clear - the cropped modes are not downsampled, they use the center of the sensor. It is not a full-sensor image that processed to a smaller size.

This is explained on pages 80-82 in the D800 manual. Also, when you use crop modes af sensors fill more of the image, so in the smallest crop mode, the entire area is filled with sensors. This would not be possible if the image was downsampled.

Crop mode and Down sample .jpg are two different things.. you can create Raw or .jpg in either crop or full. Unless I am misreading the two above statements, you are talking about two different features. The D800 and other Nikon DSLR have various crop modes.. *D7100 has DX (which is it's full sensor) and 3:1 (which is 2/3 of the sensor and gives a 2x (roughly) multiplier on the lens rather than the normal for DX 1.5x. But it can shoot lossless Raw, Lossles Compressed Raw, and Jpg Fine, Jpg Normal, and Jpg Basic. The differences are the resolution of each image but all cover the entire DX or Cropped 3:1 areas of the sensor.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

dcampbell52 wrote:

Crop mode and Down sample .jpg are two different t... (show quote)

Yes, in crop mode you only use the center of the sensor, regardless of camera. My comment was to respond to the statement that to use a crop mode on one of these cameras you take a full sensor image and downsample it to a smaller size, which is clearly not what is going on. In crop mode the extra pixels are not turned on, and there is no downsampling taking place. Fine, Normal and Basic jpg settings only apply to the amount of compression being applied - the number of pixels remain the same for the shooting mode (crop - what size, or uncropped) mode selected.