2

The first answer to this question says that

when saving images in TIFF, each pixel holds three colors' data and because of that, the file is larger... and RAW only hold monochrome data in each pixel and use RGB colored filters and hence the file is smaller

I also didn't get what it's said in the latter sentence. But, what I have learnt is, a pixel consists of three sub-pixels (as in here) (btw, dots means sub-pixels, right?) or four (as in Bayer pattern).
So the my dilemma is, doesn't a pixel hold three colors' data (in sub-pixels) whatever the format is? And did that answer say that the three or four sub-pixels hold a single color (in RAW)?
Please clear me up....

  • "Sub pixels" means something completely different from what you intend. You are talking about the color components of a pixel. – Olin Lathrop Feb 14 '17 at 12:20
4

Basically, a RAW file stores data directly from the sensor of your camera. Most DSLR are using what is called a Bayer filter (https://en.wikipedia.org/wiki/Bayer_filter) to retrieve information about color. Usually, for 4 "pixels" (sensitive elements), 2 are used to get information about green, 1 for red and 1 for blue. However, keep in mind that this sensor will provide a 2*2=4 pixels image : a sensitive element on such a sensor isn't a subpixel. I hope the following part will make things clearer :)

In the RAW file of this imaginary 2*2 sensor, you will find 4 values, coded on X bits (12 for example) => your file will weight about 4*X bits.

Because of the Bayer filter, some interpolation has to be done to retrieve color information on all pixels (see demosaicing : https://en.wikipedia.org/wiki/Demosaicing). After this step, each of the 4 pixels will have RGB values, so your file will weight 4*X*3 bits.

As TIFF file are obtained after demosaicing, they are "bigger" : each of the TIFF pixels contains now RGB data instead only R or G or B in the RAW file.

What you are calling subpixel is only related to screen : you need three LED with color R, G and B to recreate a single color (https://en.wikipedia.org/wiki/Additive_color) => a single LED is a subpixel.

You may want to take a look at those questions for more information :

2

pixel has different meaning in spheres of display technology and sensor technology. pixel of RGB Bayer sensor is represented by only one number (roughly one colour) while pixel of most of RGB graphic displays is represented by three numbers. The number of pixels noted on cameras is not the number of dots divided by four - it is actual number of dots on the sensor which become tristimulus pixels only after making a computational transformation which guesses two additional values for each dot with varying success. This is probably the reason for them to be called pixels, I am not sure.

And, surely, there is a number of file formats to store this information as it is - one number per pixel. The most common one is DNG and may hold recorded sensor data in various styles.


There is a display type used by Samsung called "Pentile" which does roughly the same - cuts the chromaticity resolution and somewhat preserves luminance resolution while introducing some colour noise. Those displays have fewer dots than one would expect when learning the nominal resolution. For example, Samsung Wave was told to have 800x480 pixels or whatever Samsung meant to say but upon closer inspection it became obvious that it has as much dots as full colour LCD panels with resolution 400x240 usually have.

  • Actually, demosaicing "guesses" all three colors. Even pixel wells filtered for green will not use the raw monochromatic value produced by that pixel well for the green part of the RGB value for that position in the demosaiced image. (This is true even after taking gamma conversion into account) – Michael C May 29 '16 at 4:31
  • @michael-clark: it is up to software to decide about it. – Euri Pinhollow May 29 '16 at 11:52
  • OK. Let me clarify. Demosaicing that results in an accurate representation of the color of the scene "guesses" all three colors. – Michael C May 29 '16 at 16:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.