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explain the difference between RAW, TIFF and JPEG
Old 01-05-2004, 11:25 AM   #1 (permalink)
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I have an inkling, but I need a technical explanation as well as an explanation in layman's terms
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Re: explain the difference between RAW, TIFF and JPEG
Old 01-05-2004, 01:05 PM   #2 (permalink)
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RAW is simply the raw data as it comes directly off the CCD, (note: this is not the same RAW format in Photoshop) no in-camera processing is performed. Typically this data is 8, 10 or 12 bits per pixel. The advantage being that file sizes are considerably smaller than a TIFF file. The image has not been processed or white balanced which means you can correct the image, and it's a better representation of the "digital negative" captured. The disadvantage is you can't open these image files with a normal photo package without using an "acquire module" (a plugin, typically TWAIN, which can open / process such images).

Tagged-Image File Format (TIFF) was developed to exchange files between applications and computer platforms. TIFF is a flexible bitmap image format supported by virtually all paint, image-editing, and page-layout applications. TIFF produces an uncompressed 24-bit per pixel image often in the multiple megabytes,.

Joint Photographic Experts Group (JPEG) format is commonly used to display photographs and other continuous-tone images in hypertext markup language (HTML) documents over the World Wide Web. JPEG retains all color information in an RGB image but compresses file size by selectively discarding data. Files sizes are relatively small, but data is lost.

Recap: RAW retains all information and is a smaller file size than TIFF, but may need translators to open the data elsewhere. TIFF retains all information, is a large file size, and is easily shared by virtually all programs. JPEG is a small file size that tosses some information to achieve this.

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Some additions and corrections
Old 01-05-2004, 04:04 PM   #3 (permalink)
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TIFF files can also hold 12 and 16 bit per color files (36 & 48 bits per pixel) and they can hold data which is compressed by a number of losless methods as well as lossy methings such as JPEG. Not all applications can understand all of the tags in a tiff file, therefore it's cross-platform/cross-application usefulness is waning.

JPEG files are 8 color bits per pixel only. If your camera can capture in 10 or 12 bit color, you'll loose color information by saving as a JPEG. Then you'll loose more stuff during the compression. It takes a keen eye or lots of compression to notice the loss however.

Finally, there is no guarentee that a CCD-RAW file MUST be smaller than a TIFF, although it usually is.
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One more correction Mark...
Old 01-06-2004, 11:29 AM   #4 (permalink)
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the pixel in any one channel possesses either 8 bit or 16 bit data, end of story. Each file therefore is determined to be either in 8 bit or 16 bit, with a total data capability of either 24 bit or 48 bit in RGB, and 32 bit or 64 bit respectfully. The color image is made of channels in grayscale only, the independent value to each pixel applies, but the compilation of all three [RGB] or all four [CMYK] total the larger bit depth number. Please keep in mind that a color channel is specific to the channel it represents and is not dispensable without changing the content of the entire file - if you move or replace a color channel, it will and does affect the entire image. For example, if I have an RGB file and I throw the G channel in the trash, the file immediately becomes a two color image of cyan and yellow, the values represented by the mix of R & B in the additive process, if I remove the B channel the file is now just cyan and magenta: These become compilation 16 bit files, but are still at just 8 bit per pixel information values, they are also known as multichannel color space (a .psd only format) and must be converted to either Duotone (eps, psd, or pdf formats only), RGB, or CMYK for output.

A raw capture can be one of many bit depths, 8 or 10 or 12 or 14, whatever, but this is determined by the combination of the camera's hardware, firmware, and software alliance; this is a manufacturer's design. Although you can create a 12 bit or 16 bit file, very little is done at this capacity due to the tremendous amounts of math involved. Photoshop CS now can apply more effects and tasks than any previous version when working in 16 bit, but even though it can, it still is cumbersome and much slower. 99% of all your color houses [Prepress], retouchers, printers, etc., work in 8 bit to color correct, enhance, or modify any file - resampling [interpolation] is probably the primary assignment for 16 bit data - and all printing devices are default to 8 bit.

Tiff is a lossless format with an independent directory capability far superior to most [all] file formats - it virtually is the best and most universal file format - this is why it is a larger file. Jpeg on the other hand actually has automatic limitations and with compression, file deterioration built in by degree of loss vs. size. Jpeg can be RGB or CMYK, but only 8 bit - 24 bit RGB & 32 bit CMYK. If you save a file in jpeg and compress it at say a Quality value of 7 with a Standard Baseline, the information of color is averaged in pixel sets or clusters of 4 square pixels, averaging some of the values out. Then if you save that same file again in jpeg at say Quality level 6 and Optimize the Baseline, you will make larger clusters or sets - still in groups of 4 pixels, just larger areas - averaging information, making the data content reduce in file size. This is also what causes tremendous artifacting and edge deterioration in contrasting pixel order.

Robert

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