Jorge Parra wrote: > >>> Does >>> anyone have experience of shooting unfiltered in fluorescent light >>> and successfully correcting in Photoshop? >> >> Shoot a Macbeth Color Checker and use that to set the initial >> Black/White/Greypoint in curves and save the curve. Apply this curve as a >> starting point for the real images. > > Dear Thomas, I have great curiosity about this info. Is this just so > simple? It's not so simple, but if you do colour correction and set a white point, black point and an (optional) grey point, you have a neutral grey balance 90% of the time. And when the grey balance is nailed down the rest is a question of hue/sat and possibly selective colour adjustments to make skin tones and memory colours appear pleasing.
> If so, what is the use or rationale to include all other color > patches in the card ( 24 in total)? If setting black, white and grey is all you do, the other patches are irrelevant. However, I'd still recommend to use a Macbeth over a Kodak grey wedge (or similar) because the spectral reflectance of the Macbeth neutral patches are much superior to anything else I've tested... > I find that if I set ( in Levels) the White point first ( at a value of , > say 245 instead of 255) and followed by the Black POint ( set at 10 or 15) > then there is no way I can have the Grey point to fall in the Expected 128 > target value. It depends on your light source. The fuller spectrum the easier this is. The more whacked the fluorescent light is the more adjustments you need to do to obtain a pleasing image. By saying "there is no way I can have the Grey point" do you mean A). it doesn't fall there by default, (in which case I'd say click the grey eyedropper on a neutral patch -the one measuring closest to 128 in RGB). B). that if you set the grey eyedropper the image as a whole "appears" wrong (in which case my answer would be then slightly adjust the points of the curve in the R+G+B channels). > THis is odd to me and still have no defined workaround for > this, specially since it has happened on some ocasions that the order of the > color sampling( Black first of Grey first) introduces changes in the > overall values. You can only place the grey after the black or white. When you click with either the white or black eye dropper any other adjustment to the (R+G+B) curves is erased. Check the individual channels after setting white, black and grey (in that order although you can do black before white). > > Do you have a formal, foolprof way to set a standard calibration with this > Color Card Checker ( by GretagMacbeth)?? There is no such thing as foolproof <G>. I either do as above or I build a camera profile (or scanner profile) which will take care of both the neutrals and the colours. It's still only a starting point though. If the images you shoot differ from the conditions you shot the target in, this method will be less accurate. Ultimately it's about making an image visually pleasing, not about making all colours appear colorimetrically "correct". > > I will really thank you for being as detailed as possible in your > explanation. I have been working with the card for sometime, and even though > it has helped me somehow, still there are some "holes" in the behaviour of > it ( at least when using a Canon D60). Explaining a work method is no easy task if you want to do it right. A lot depends of the lighting conditions, how you neutralise the camera, the way you shoot the card, the general lighting situation, and does the lighting on real images differ form the Macbeth target and then some. All I can say (with my present workload) is what I already have said, and this: Set the white point, then the black point. This will fix the tonal range and make highlights and shadows neutral. Then try with the grey eyedropper. If the grey doesn't work either delete the points in the RGB curves or try to adjust them to make things look right. Then do either hue/sat or selective colour. THEN play with making selections if you still have areas that does not appear as you want them. This procedure goes for most any type of colour correction in this world. If you want to take it beyond this you are deeply involved in channel blending and blending modes in general, but that is a bit too esoteric to discuss here (I teach courses though)... > Checking the Color values (Info Pallette in PS7) of the Card's Patches > introduces the obvious need to run a full set of Selective Color adjustments > to get close to their target values, so a simple Black/ White and Grey > Points is not good enough according to my tests. It follows then that files > shot in same conditions should also be loaded with all those adjustments. The first year or so I was shooting digital on a lead DCB I (brick) we had a scanner operator helping us build a good conversion into CMYK from the untagged camera files. We shoot a Macbeth he plugged in various adjustments to the colour (first in Scitex ColorShop, then in AGFA's Photone, and the goal was to make the cromalin match the Macbeth. After some hundreds adjustment and hundreds of cromalin's we had a real good match. Only when we used this conversion on real images we had severe banding which was beyond repair. The morale is, just because the colours in a Macbeth colour checker is correct, it doesn't mean that real life images will be. Consequently if your image looks pleasing, who cares what the Macbeth colour checker looks like, unless your task is to shoot a reproduction of this particular target... Best Regards Thomas Holm / Pixl ApS - Photographer & Colour Management specialist - Adobe Certified Training Provider in Photoshop� - Imacon Authorized Scanner Training Facility - Remote Profiling Service (Output ICC profiles) - Seminars speaker and tutor on CM and Digital Imaging etc. - Home Page: www.pixl.dk � mail:[EMAIL PROTECTED] -- =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
