Does a RAW image have dimensions?

Discussion in 'Digital Darkroom' started by joel_b.|1, Jul 14, 2011.

  1. That's my question. It sounds kind of metaphysical, no? It also may be really dumb. Does a RAW image have an intrinsic size -- so many pixels x so many pixels -- or does the image not become "realized" in that way until it's exported as a jpeg, tiff, etc.?
    I'm so grateful to know that I can turn to this forum with even my dimmest questions.
  2. The image sensor has photo sites (sensor pixels) arranged in a grid. X pixels wide, Y pixels tall. The RAW file records the data from each of those pixels - no more, no less. So, yes, it has real dimensions in that it records data about a precise number of pixels, arranged in a specific way.
  3. "so many pixels x so many pixels"
    As far as pixel count goes yes the raw file will have the exact same amount of pixels (or should anyways) as a jpeg from the same camera. If the jpeg is 3000x4000 then the raw file will have 3000x4000.
  4. Does a RAW image have dimensions?​
    Yes, and as defined, set and processed by the camera used at the moment of pressing the trigger. For e.g. Raw, Medium Raw, Small Raw.
    You can take a small RAW and expand it to the dimensions of a full sized Raw (or larger, or twice, thrice or four times as large), but you're still stuck and playing with the data/info captured intially. The same apples to the second step of then preserving and using it when converting to the more practical Tiff and jpeg formats.
    In short. the best you and your camera can do is to capture at full sized RAW.
  5. Many thanks, gentlemen. My journey to understanding resolution is a step further along.
  6. "My journey to understanding resolution is a step further along."

    To push it another step along: Nobody who answered your question said anything about "resolution", which in this context means "pixels per unit of measure". They were talking about the only thing that really matters, the pixel dimensions.

    The resolution of a photo is just a number you set as a parameter, either in the file itself, or in whatever metadata the processing program associates with the file. Common numbers are "72", "180", "300", and so on. Sometimes the number goes into some calculations that affect print size, but you can change the number at print time and, in fact, I usually do.

    If the resolution is, say, 300 ppi (pixels per inch), and the pixel dimensions are, say, 2400x3000, then this means that the image is 8x10 in. You want bigger or smaller? The pixels are still the pixels, so just change the resolution number. (Do NOT resample!)

    The resolution number has no effect when displaying the image in a browser, and rarely has any effect anywhere else, either.

    Raw images have a resolution, too, since it's just a number. The image has to be rendered to be printed, and that's the number that will be used.

    Hope this didn't make things much worse... ;-)
  7. Spearhead

    Spearhead Moderator Staff Member

    Resolution is not ppi for a digital file. Resolution is x pixels by y pixels. PPI is only of value at the time an image actually has a physical dimension, i.e., it's printed. Even then, it's simply a ratio between inches and pixels and as such, meaningless by itself.
  8. I think the answer to this is yes, a raw image has dimensions, but as to how many pixels this is there are a couple of resons why this is not always the total number of photosites, or necessarily the same as in a maximum resolution jpg.
    Firstly not all photosites are always used in making the image - those at the extreme edge are sometimes not used - look at the data for the camera and you can sometimes see a difference between the number of pixels and the effective number of pixels. For example the Nikon D700 has 12.87 pixels, but only 12.1 are used to make up the image.
    The major reason for uncertainty however is that in most digital cameras the sensor is covered in a mosaic filter so pixels are recorded as red, blue or green monochrome only. These are your raw image. Software interpolates this into coloured images from each pixel, however images can be produced with more pixels than there are effective photosites - it is solely the software producing the jpg that calculates them, and it can calculate more or less by altering the algorithym. I don't know of any digital SLR that does this, but it was certainly used in cheap point and shoot digital cameras to up the number of pixels, while still using a cheap sensor.
    Basically than, a raw image will usually have the same number of pixels as the effective number of photosites (not the total number) and often has the same number of pixels as in a maximum resolution jpg (but these are real monochrome pixels, and not full colour manufactured pixels, of which there may be more or less than in the raw file)
  9. Resolution is x pixels by y pixels.​
    @Jeff if you mean something like 3000 by 2000 pixels then I disagree, however, if you mean the final figure of 3000 multiplied by 2000 then I agree. 6 million pixels is the resolution and not 3000 by 2000.
  10. @Jeff if you mean something like 3000 by 2000 pixels then I disagree, however, if you mean the final figure of 3000 multiplied by 2000 then I agree. 6 million pixels is the resolution and not 3000 by 2000.​
    Maybe semantics here but Iā€™m OK with someone saying the resolution of the raw is 3kx2K and not 6 million pixels (or megapixels). Knowing the total number of pixels is far less useful than knowing its pixel dimensions if your goal is understanding resolution and what you can output with said pixels.
    Saying you have 6 million pixels is no help at all in deciding what print size you can generate from that data. Saying you have 3000x2000 pixels gives you all the information you need to do this.
  11. Yes, semantics. I agree with your explanation.

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