Cameras forum

General discussion

Pix Size

by husadawg / November 23, 2005 1:51 AM PST

I have two camera's, a Sony DSC850 4.1MP and a Nikon Coolpix 4600 4.0MP. When each is set to highest resolution mode, the picture size with the Sony is something like 27 inches by 32 inches. With the Nikon it is 5''x 7''. The picture quality with the Sony is excellent and does not appear grainy, even at the largest size and I can shrink photos to whatever size I want prior to printing without losing quality. With the Nikon, if I try to go larger than 5x7, picture quality is noticably degraded.

I don't understand what determines picture size. I thought it was pixel density but clearly there is something I am misunderstanding. Any illumination is appreciated.


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Sony DSC850 - Unable to Locate such a camera.
by snapshot2 Forum moderator / November 23, 2005 6:30 AM PST
In reply to: Pix Size

Can you provide a link to a Sony SDC850 camera?


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Sorry, Typo Error
by husadawg / November 23, 2005 8:04 AM PST
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Re Pix size.
by Papa Echo / November 23, 2005 9:06 AM PST
In reply to: Pix Size

Both set to highest resolution, but photos are of different quality. What about the compression settings ? Perhaps the Sony is set at the lowest compression(e.g. super fine), while the NIKON is at the highest ? Or perhaps you are using the uncompressed format with the SONY ? ''Uncompressed format'' is not available with the NIKON.

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Along with the pixels recorded ...
by ChuckT / November 23, 2005 9:46 AM PST
In reply to: Pix Size

Since both cameras have nearly the same pixel count (4MP vs. 4.1MP) you would expect the pictures to come out nearly the same quality. But there are still a couple of things that will affect the picture quality.

For one thing, there are the optics. One camera may have better lenses than the other. (glass vs. plastic?)

There is the compression algorithm used (inside of the camera electronics) for the JPG compression. You may be able to adjust how much loss you will accept in the JPG compression. (The JPG format is an adjustable compression, where more compression results in more loss of detail.)

By the way, you might compare nearly identical pictures snapped with both cameras, and compare the JPG file sizes. If there is a substantial size difference, then that quickly tells you that the camera with the smaller JPG file size is ''dialing in'' a more lossy compression ratio.

OR, when you take pictures, you could possibly use the RAW image, if that is available. RAW is absolutely uncompressed, all the picture data is there, and it is the format that many professionals only work with. (I don't, but I don't have a discerning eye.)

As for the wild difference between the 27x32'' and 5x7'' picture size, that is one more thing that gets recorded into the picture data. There are data parts that tell the software, used to print or view your pictures with, that say what the captured DPI (Dots Per Inch) is.

It sounds like the Sony might be at around 70 DPI to gets those nearly 30 inch numbers. Your Nikon must have its setting at around 300 DPI. There is also another bit of data that can be recorded in with the picture that says what the overall final hard copy picture size is. But all of those data bytes can be overrode. They make using some image viewer/printing programs easier to use, some harder, and some just get in the way.

Your pictures may have none of that data recorded in with the actual picture, some of it, or all of it.

It really does not matter if it is there, since you can use other software to override, change, or ignore, any of it. Check out IrfanView, for a great multifaceted graphics viewer and printer (and some say editor).

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Cameras do not capture images in dpi. That is printer
by Kiddpeat / November 24, 2005 9:03 AM PST

terminology. Cameras capture pixels. Pixels are not at all the same thing as dots. Cameras do not decide how many pixels per inch. That is a display and/or printing decision. The camera simply records a given number of pixels.

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you are right, but DPI info can still be in the data
by ChuckT / November 25, 2005 12:12 AM PST

You are correct, cameras do not capture with any relevance to DPI, because how could it relate to anything? an inch of what? But there are fields in the information fields of the JPG format that provide for things like DPI (or SPI or PPI or resolution, or whatever you might refer to it as). Actually for capturing pictures the DPI info is more used when related to with the capturing of images with the use of a scanner.

The JPG format is a versatile format used by cameras, scanners, even graphic creation programs. There are fields that may be used by some of those devices that have no use in those other devices.

There are plenty of other fields, like the EXIF (EXchangeable Image Format) data, which has space for ''ImageDescription,'' make and model of the camera, date and time, exposure time, FNumber, MeteringMode, etc.

Then there are provision fields for the IPTC (International Press Telecommunications Council) data, that while not normally recorded by the common digital camera or scanner, it could be done with elaborate devices. Those fields are typically entered and used by professionals to record category information, keywords, special instructions, credits, etc.

So, I did not mean to infer that a camera records any relevant DPI setting, but it could be that the JPG images that husadawg now has may have the fields for DPI now set (however it may have been set) and that could be affecting his (or her) viewing and/or printing with whatever software he/she has.

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I'll say it again, and then drop it.
by Kiddpeat / November 25, 2005 1:48 AM PST

'But there are fields in the information fields of the JPG format that provide for things like DPI (or SPI or PPI or resolution, or whatever you might refer to it as).'

DPI (dots per inch) and PPI (pixels per inch) are not the same thing. Further, PPI is not contained in the image's EXIF information. PPI is a display parameter which is not relevant to the image data. The number of pixels is, of course, contained in the image information. The pixel is the basic building block of the digital image, and the number of pixels in an image must, of course, be known.

DPI tells a printer how many dots are to be used in rendering an image on a piece of paper. It is totally unrelated to pixels or pixels per inch. For example, I could print a very acceptable image on my Epson 2200 by using 150 ppi (pixels per inch) to form the image. I would, however, tell the printer to use 1,440 dpi (dots per inch) to render the image. The 1440 number is used because it has been shown that anything less will result in a noticeable loss of detail in the print. I could just as well use 2,880 dpi, but the resulting image will look no different. In either case, the 150 ppi number is irrelevant to the dpi chosen.

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good, then I'll continue
by ChuckT / November 25, 2005 4:54 AM PST

Correct, DPI and PPI are not the same thing, I do know the difference. I also did not say they were the same thing, I said ''whatever you might refer to it as'' But, they can so easily be transposed in general discussions of graphic images. Sort of like talking about bison and buffalo when talking about those related animals, or even dolphins and porpoise, yadda, yadda, yadda :).

All this is apparently a matter of definitions and interpretations between us. I am not wanting to debate, just to clarify my thoughts. I do not doubt your apparently through knowledge and experience. None of it is needed by husadawg to help resolve his different results for photographs from two different cameras. I was just letting him know that there is more to picture clarity and final hard copy size than simply the picture resolution alone. Hopefully some of this info, from us, can explain more than (I am sure it) does confuse.

Dots (or spots) are the smallest image element you want separately defined when scanning. Pixels (picture element) are the smallest image element you have on a display (containing the full color info for that single element) (I note that because there are some display softwares that further define sub-pixel info, such as MS ClearType, for apparently smoother image edge transitions).

DPI is a setting, and there is not a separate field for pixels in a JPG file. Dots are typically referred to with scanners, and Pixels are generally referred to when talking about images on a computer display.

You set a scanner to scan at so many dots per inch. When scanning at a larger DPI setting (more dots per inch) will result in a larger file. But when a camera takes a digital image, and stores it as a JPG, the DPI field may get set, even though it is irrelevant.

And I did not say that DPI setting was in the EXIF data. I said, after mentioning DPI, that there were other possible fields in the JPG format, like EXIF. I am sorry if you misinterpreted it as the same area.

If you look at the details for EXIF, there are possible fields for XResolution and YResolution, which, when recorded, can be used for the 'optimum' display setting. That is essentially PPI, but not exactly.

I can change the recorded DPI setting in any of my JPG files from 1 DPI to thousands-of-Dots PI, and it would not necessarily change the file size, nor my displaying resolution (this is the setting after the scanning, not for, and prior to, the scanning). It is just a setting, and my software (IrfanView, among others) can ignore it, to get the display size or print size that I want. Or I can have my printing follow the setting of the DPI to get the defined hard copy size (up to the capability of my printer).

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OK, I'll stand partially corrected. I'm finding a lot of
by Kiddpeat / November 25, 2005 6:57 AM PST

mixing of terminology on the net, so it looks like the definitions are somewhat ambiguous. I understood that the color components of a pixel are, technically, called pels, but I'm also seeing them referred to dots. I wouldn't refer to these using the term dpi.

My scanner, a Microtek 6800, refers to ppi, but never to dpi. Similarly, every scanner I've used refers to ppi. I've never heard dpi applied to scanners.

Digital cameras also always use the term pixels. When they do so, they are referring to an image component, not a display.

Photoshop can vary the size of an image by changing pixels per unit of measure (inches or cm). It does not refer, as far as I know, in any way to dots.

DPI is not typically encountered until one wants to print an image on an inkjet. It may be used in other printing processes also, but I am familiar with its usage with inkjet printing. An inkjet is told how many dots per inch it should use to print an image. For my Epson, the choices are 740, 1440, and 2880. The printer also knows what the ppi is, but the two measures are totally different from the printer's point of view.

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it's all cool
by ChuckT / November 25, 2005 8:13 AM PST

Lots of terms, all somewhat related and easily confused or interchanged. That is why I try to be 'ambiguous' or use parens (other terms, like 'whatever's), and hope that the reader understands the confusion.

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