I cannot learn if I do not ask!

[cowcrzy06]

Hello Friends!

Can someone explain Raw , Jpeg Etc. I feel embarassed asking! But as I said above I cannot Learn If I do not ask . If it is easier I would love to read an article. All I ask is to please keep it as simple as possibile! Thanks In Advance!! You Guys & Gals are GREAT!!

[Ian]

Re: I cannot learn if I do not ask!

Hello Friends!

Can someone explain Raw , Jpeg Etc. I feel embarassed asking! But as I said above I cannot Learn If I do not ask . If it is easier I would love to read an article. All I ask is to please keep it as simple as possibile! Thanks In Advance!! You Guys & Gals are GREAT!!

No problem

When the picture is taken, it only exists as a matrix of elctrical charges on the sensor chip (which is where the film used to be in film cameras). Basically, each image pixel is represented on the surface of the chip by a photo-electric cell, pr photosite, that generates a tiny electrical charge according to how much light it traps during the exposure. In fact the sensor of a digital camera is an analogue device, not digital!

The digitisation happens when the camera measures the charges of each pixel and converts each charge value into a number. The number produced represents the density or brightness of that pixel. Some pixels are recorded as shades of red, others blue, other are green. This is because a single colour filter (Bayer filter in most cameras) lies above each pixel position on the sensor chip.

So the most basic image information is an array of red, green and blue pixel values. You can't get simpler or more pure than that. This data is the 'raw', or unprocessed, data that the camera works on to eventually produce a recognisable picture.

Every digital camera produces raw image data, but only some, usually more sophisticated models, record this raw data for the photograhger to use later. Most cameras simply use it once, by processing it to produce a normalised colour image which is stored, after which the raw data is discarded.

If you viewed an unprocessed raw image, it would look very odd as it would only contain different densities of red, green and blue pixels. And in most cameras there are twice as many green pixels as any other colour. so the colour would look very artificial and fine detail would look like a red, green and blue mosaic. The picture would not be sharp and the contrast would not be correct. It would not be a recognisably normal photograph.

But the camera has been pre-programmed to process the raw data. It de-mosaics the image, combining the the RGB values around pixel positions to produce a true colour value for that pixel. The process of using adjacent pixel data to build a new image structure is called interpolation.

Once the pixels have been coloured correctly, the camera uses data, including the camera exposure modes, plus analysis of the colour distribution and density of the image, to normalise the colour balance, contrast and sharpness.

The camera's version of your image is complete. This picture data is then usually stored as a JPEG image file on your camera's memory card. A JPEG image has been processed further to reduce its digital size without adversely affecting visible quality. This can be done because not all the image data represents visible information in the image. The unneeded information is lost permanently. If you re-save a JPEG file, it is compressed again and more data is eroded from the picture and degradation begins to be visible.

The amount of data elimination in JPEG image compression is variable - you can lose little and maintain a high level of quality but end up with fairly large files, or you can lost a lot of data and get very small files, but those files, when displayed, would show telltale signs of over-compression, in the form of blocky digital artefacts and irregular shades of colour. The norm is a level of compression somewhere inbetween these two extremes.

But JPEG files are very space thrifty. A typical 5 megapixel JPEG camera image file could be around 2 megabytes in size, but its uncompressed 24-bit (8 bits per pixel, per colour channel) size would be 5x1024x1024x3x8 = 125829120 bits or 15 megabytes.

Back to RAW files - more sophisticated cameras store these in a proprietary raw file format that can be re-used later. As the data is very pure, you can manually build your preferred version of the scene photographed with the minimum of compromise. If you try to enhance or alter a JPEG image, which has already been processed and lost much of the original image data, you are much more limited in what you can do before nasty distortions, like noise (grain) digital artefacts (blockiness) and dynamic range limitations show through.

Lots of people like the analogy of RAW image files being the digital equivalent of a film negative. It's easy to view and copy a print compared to a negative and it's eaier to store and view a JPEG file than to store and view a RAW file. With a negative, you have all the original quality of the image and the same is true of a RAW image file.

I hope that helps - I can expand on this in particular areas if it's still not clear - just let me know!

Ian

[Stephen]

Re: I cannot learn if I do not ask!

Don't encourage him Cowcrzy06, he gets boring when he is in techy mode

[bigbob]

Re: I cannot learn if I do not ask!

Don't encourage him Cowcrzy06, he gets boring when he is in techy mode

I've read many explations about RAW V Jpeg on various forums but never such a detailed one .
Can't add a thing .

B..

[Ian]

Re: I cannot learn if I do not ask!

Don't encourage him Cowcrzy06, he gets boring when he is in techy mode

Hah!

Ian

[lumix]

Re: I cannot learn if I do not ask!

Well I never. That was most informative. Now I know a whole lot more than I did ten minutes ago. Thanks Ian.

[cowcrzy06]

Re: I cannot learn if I do not ask!

Thank you for the laughs, after my day I sure needed it but seriously Ian thanks for the info. I did learn alot!

[Pops]

Re: I cannot learn if I do not ask!

You guys can laugh all you like but I for one printed it out to keep for a while

Oh boy will I be able to impress folk