Thread: Workflow
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Old 08-18-2008, 04:59 PM
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Default Re: Work Flow

Quote:
Originally Posted by ColinWhite View Post

Why would you want to convert to a JPEG , It's a half rate picture format. Its compression routines lose quality, I dont know if you know this ( read up on JPEG compression techniques ) all my Digital shots are saved raw and in .TIFFS if then I want to publish them on the web I make a copy of the pic and down grade size and quality and publish as a .gif

Colin, in choosing the best file format the most important factor is the destination for that file.

TIFF (Tagged Image File Format) is a completely "lossless" format, so it will retain all of the original image information. That's good, but these files are also very large, and the only way to reduce their size is to reduce the resolution, and that's not good if you need to reduce it too much.

JPEG is a compression format, so of course it is considered a "lossy" format, but it's size is reduced both by lowering resolution and/or removing image information. For most tonal images, a lot of color information can be removed without resulting in a noticeable difference to the eye (most eyes). This results in a smaller image file but still with decent resolution. The quality of this image depends on the quality of the conversion software, the amount of compression you need, and the number of times you compress it. Every time you open a JPEG, modify it, and then save it back to JPEG more information is lost in the compression process.

GIF files are "index" files, which means they are produced with a color set in the hundreds (or as low as only a few) instead of millions as with RGB or CMYK. These files are generally very small, but they do lose a lot of image quality in the process. You will never be able to produce bright colors with a GIF, they are best for images with solid colors or pastels. They almost never print well, but are great for the Internet because of their small size.

Files that will be viewed only on a monitor (or simliar device) are best left in the RGB (additive primary colors) color space, because that is how they are reproduced on the screen. And any resolution higher than the display device, usually 72-96 ppi (pixels per inch) is a waste of file space.

Files that go to an inkjet will automatically be converted to the CMYK (subtractive primary colors) color space by the printer's RIP (Raster Image Processor) because that is how they are reproduced. Since CMYK can produce fewer colors than RGB, the RIP must replace many colors with something close by using a CLUT (Color Look Up Table). Some color information is lost, but with a good quality image it is usually not noticeable to the eye (most eyes). Inkjets with more than four ink colors generally have variations of the Cyan, Magenta, Black. This increases the number of RGB colors that can be reproduced by CMYK and is often called CcMmYKk. Clean Blacks and Grays are a big problem for CMYK, so if a Gray ink is present it greatly enhances the tonal aspect of an image.

And most printer RIPs tend to discard any resolution over 200-300 ppi, so any resolution over that is a waste of file space.

So, what was your original question again? Why would I use JPEGs?
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