andrew_rodney1

No a useful tool for color management. You need a Spectrophotometer. A densitometer

will only read density values where a Spectrophotometer reads color based on the

spectrum and is what is necessary to build ICC profile.

Andrew Rodney

http://www.digitaldog.net

There's no reason to convert to Lab to do this (and a lot of reasons not to convert). There

are some editing techniques that can be conducted on an RGB file but produce nearly

identical results of converting into Lab by using the Luminance blend mode in Photoshop.

For example, instead of converting a file to Lab to sharpen just the L channel, apply

Unsharp Mask on your RGB file, then under the Edit menu, select the Fade command and

set the mode popup to Luminosity. Not only will this produce the same qualities as

sharpening on the L channel (without having to do a color space conversion) but the

Opacity slider is useful for fine-tuning the effect.

It is true there are a few correction techniques that rely on a document being in Lab color

space. The question becomes is it worth going through the time and worse, image

degradation to convert from a working space to Lab and back again? Every time a

conversion to Lab is produced, the rounding errors and severe gamut mismatch between

the two spaces can account for data loss. The amount of data loss depends on the original

size and gamma of the working space. For example, if the working space is Adobe RGB,

which has 256, values available for neutrals, converting to 8-bit Lab reduces these down

to 234 values producing a loss of 22 levels. Doing the same conversions from ProPhoto

RGB reduces the values to only 225 producing a loss of 31 levels. Bruce Lindbloom a well

respected color geek and scientist has a very useful ﾓLevels Calculatorﾔ that allows one to

enter values to determine the actual number of levels lost to quantization (see the ﾓCalc

pageﾔ at http://www.brucelindbloom.com). One problem with Lab is itﾒs a huge color

space and if youﾒre working in 24 bit images, you have three channels of which each

contains 256 possible values. The data points in an 8 bit file are farther apart in a larger

space. That can cause banding in certain images (skies, smooth areas like the fender of a

car, etc).