stevem@hpvcfs1.HP.COM (Steve Miller) (01/05/90)
I recently purchased the color scanning package Chroma-32 from Discovery Software. This package supposably lets you get color scans using your greyscale scanner by scanning the image three times with three different color filters (plastic 8.5X11 sheets) I have a ScanJet+ 256 level scanner. The process works like this: You tape the sheet to be scanned to the top of the scanner bed. You do a pre-scan and define the area you want to scan. Then you slip each color filter under the sheet and scan it once for each filter (red, blue, and green). The result is a color scan displayed on the screen. Various controls over resolution, contrast, brightness are available and the results can be saved in a couple of different file formats. The Problem: The color scans don't have good color and I think I know why: The color filters suck! The red filter doesn't block all of the blue or green. The green filter doesn't block all of the red or blue light etc.. The result is muddy looking (under saturated) colors. An easy test demonstrating that the filters aren't very good is taking a picture with lots of color and placing one of the filters over it (say the red filter). In theory you should only see red color coming through: whites and reds should be a bright red and all other colors should be darker shades of red or even black. However, this is not what you see. The red filter allows fairly large amounts of green and blue to come through. Likewise the green and blue filters allow other colors to come through. I played around with some red plastic sheets that I found around the office and came up with better colors in my scans, but still not good though. It's as if the people who did Chroma-32 just went down to K-Mart and picked out the first colored plastic sheets they saw. This is a $595 package and I was able to find a more effective red filter sitting in our office supplies at work! I've tried to call the product assist line several times with no answer so I'm wondering if anyone else has had experience with the product. Also does anyone know where I could get decent quality colored plastic sheets to test as filters? I especially need a good red filter, but I suspect that all of the filters can be greatly improved. I still haven't ruled out the possibility that something isn't set up correctly so in the meantime I'll just keep calling their help line. In theory you probably don't need perfect color filters if you have the properties of the filters characterized. You can then compensate for the inaccuracies using a series equations for each pixel, but I suspect they don't do this. Thank you in advance, Steven Miller ...!hplabs!hpvcfs1!stevem Vancouver Division Hewlett Packard
briand@tekig5.PEN.TEK.COM (Brian Diehm) (01/05/90)
>The color scans don't have good color and I think I know why: The color >filters suck! The red filter doesn't block all of the blue or green. The >green filter doesn't block all of the red or blue light etc. > >I played around with some red plastic sheets that I found around the office >and came up with better colors in my scans, but still not good though. > >Also does anyone know where I could get decent quality colored plastic sheets >to test as filters? I especially need a good red filter, but I suspect that >all of the filters can be greatly improved. I would consider Kodak gel filters, if they are large enough. They make the filters used in industry for color separations, and have separation primaires in their product line. A generic "photographic red" filter (#25) will exhibit the properties you seek - making everything you view through them appear in the range from pure red to pure black, with no other color evident. Generally, gel filters are available in 3-inch and 4-inch squares. These are pretty fragile (fingerprints and moisture will RUIN them, not just damage them) and they tend to go for about $20 each - they're not cheap. There also exists a Kodak filter databook that gives the spectral response of each of their filters. If you need specific references, I will look them up for you. -- -Brian Diehm Tektronix, Inc. (503) 627-3437 briand@tekig5.PEN.TEK.COM P.O. Box 500, M/S 39-383 Beaverton, OR 97077 (SDA - Standard Disclaimers Apply)
rieman@boulder.Colorado.EDU (John Rieman) (01/05/90)
In article <19640005@hpvcfs1.HP.COM> stevem@hpvcfs1.HP.COM (Steve Miller) writes: >... Also does anyone >know where I could get decent quality colored plastic sheets to test as >filters? Try an art supply store that carries Pantone products. Pantone makes (or used to make -- I haven't bought any for a while) transparent plastic sheets that graphic artists use when producing drawings that need very evenly colored sections. Another potential source is a theatre lighting supplies store. Ask for the "gels" used on stage lights. (These probably don't have the optical quality or the transmission characteristics you need, but it might be worth a try.) Finally, if there's an industrial plastics store in your area, they will probably have colored plexiglass. In Denver, I'd go to "Plasticrafts," a regular haunt of artists, art students, and makers of neon signs and custom displays. -john rieman@boulder.colorado.edu U. of Colorado