Scanning Slides

[Steven Ruttenberg]

That is possible, but if that is the case, then you should not get a color image with just raw data, yet I do. I would think the scanner has a bayer filter on it so it is already baked into the raw data. That would have to be the case, otherwise even the simple act of just inverting a raw negative in ps would not give you color. If you mean demosaicing or debayering, then an actual raw converter like camera raw would be needed, but I suspect (could be wrong) that the scanner does this automatically. This is still raw image data, from that standpoint. But, not knowing much about what the scanner is doing, I could be wrong. Color perfect does not do demosaicing/debayering that I know of. I am trying some things out, but definitely the slide was underexposed.

[Ted Baker]

That is possible, but if that is the case, then you should not get a color image with just raw data, yet I do. I would think the scanner has a bayer filter on it so it is already baked into the raw data. That would have to be the case, otherwise even the simple act of just inverting a raw negative in ps would not give you color. If you mean demosaicing or debayering, then an actual raw converter like camera raw would be needed, but I suspect (could be wrong) that the scanner does this automatically. This is still raw image data, from that standpoint. But, not knowing much about what the scanner is doing, I could be wrong. Color perfect does not do demosaicing/debayering that I know of. I am trying some things out, but definitely the slide was underexposed.

I am not referring to demosaicing/debayering, I am reffering to matrix algebra. The process of adjusting the values of each RGB triplet to a known colorspace like sRGB. For example if you had raw RGB values of 65535,0,0, you would have red, but what kind of red would it be?

[Peter De Smidt]

Personally, for slide scans I scan with as few software adjustment made in the scanner as I can. When bringing into Photoshop, I apply a custom icc profile made with Wolf Faust's IT8 targets, and then convert the color space of the file to my editing working space. It's important to use an IT8 file made with the type of film that you are scanning.

[Steven Ruttenberg]

I am not referring to demosaicing/debayering, I am reffering to matrix algebra. The process of adjusting the values of each RGB triplet to a known colorspace like sRGB. For example if you had raw RGB values of 65535,0,0, you would have red, but what kind of red would it be?

Okay, that makes sense. There is no color space assigned to the raw file so I do that in PS.

[Steven Ruttenberg]

Personally, for slide scans I scan with as few software adjustment made in the scanner as I can. When bringing into Photoshop, I apply a custom icc profile made with Wolf Faust's IT8 targets, and then convert the color space of the file to my editing working space. It's important to use an IT8 file made with the type of film that you are scanning.

I will need to photograph my xrite colorchecker target that I use for my digital camera. I can create a "camera" profile for each color slide film type I use and then apply that in camera raw or Lightroom.

[Peter De Smidt]

That is not as good of an approach as using an IT8 reference slide. Such a slide is meant to cover the full range of the emulsion. A color checker doesn't do that.

[Steven Ruttenberg]

That is not as good of an approach as using an IT8 reference slide. Such a slide is meant to cover the full range of the emulsion. A color checker doesn't do that.

Okay. So then I would need to get an it8 target to photograph as you mention above.

[mijosc]

http://www.targets.coloraid.de/

I think doing a proper IT8 calibration with a target of the same film stock you are scanning is critical to getting good color from the scanner. When I first started scanning, I had a terrible time getting decent color from Provia slides when my scanner was calibrated with the Kodak target. Also, I have tried raw scans of transparency film into ColorPerfect and have had less than acceptable results, although I do like it for negative film.

My workflow with transparency film is:
1. Make sure scanner is calibrated with the film stock I will be scanning.
2. Make sure all automatic adjustments and sharpening is turned off.
3. Make sure I'm scanning at 48-bit (16-bit per channel.) (I don't bother with infrared cleaning since I prefer to spot manually in Photoshop later.)
4. Scan film at highest resolution scanner will allow (6400dpi on the Epson V7xx/8xx)
5. Bring the scan into Photoshop
6. Downsample by a factor of 3 or 4 (2133 or 1600 DPI on an Epson V7xx/8xx) using Bicubic (Smoother). This gets me close to the actual resolution of the scanner.
7. Do some quick spotting for dust (how much I do depends on how much I like the image.)
8. Save the image.
9. Import into Lightroom
10. Apply a preset created from a previously scanned IT8 target with exposure, black/white points, sharpening, and color temperature set.

However, even with the most rigorous scanning workflow, underexposed slides are really tough to work with on most commercial scanners. They just don't have enough DMAX to really resolve details in the shadows (this is especially true with Velvia.) I have some darker slides with look ok on a light table, but just turn to muddy mess when scanned. I've tried multi-exposure, but just still can't seem to get there with my equipment. I think, if the image is worthy, those are likely good candidates for a professional Flextight or drum scan.

[Steven Ruttenberg]

http://www.targets.coloraid.de/

I think doing a proper IT8 calibration with a target of the same film stock you are scanning is critical to getting good color from the scanner. When I first started scanning, I had a terrible time getting decent color from Provia slides when my scanner was calibrated with the Kodak target. Also, I have tried raw scans of transparency film into ColorPerfect and have had less than acceptable results, although I do like it for negative film.

My workflow with transparency film is:
1. Make sure scanner is calibrated with the film stock I will be scanning.
2. Make sure all automatic adjustments and sharpening is turned off.
3. Make sure I'm scanning at 48-bit (16-bit per channel.) (I don't bother with infrared cleaning since I prefer to spot manually in Photoshop later.)
4. Scan film at highest resolution scanner will allow (6400dpi on the Epson V7xx/8xx)
5. Bring the scan into Photoshop
6. Downsample by a factor of 3 or 4 (2133 or 1600 DPI on an Epson V7xx/8xx) using Bicubic (Smoother). This gets me close to the actual resolution of the scanner.
7. Do some quick spotting for dust (how much I do depends on how much I like the image.)
8. Save the image.
9. Import into Lightroom
10. Apply a preset created from a previously scanned IT8 target with exposure, black/white points, sharpening, and color temperature set.

However, even with the most rigorous scanning workflow, underexposed slides are really tough to work with on most commercial scanners. They just don't have enough DMAX to really resolve details in the shadows (this is especially true with Velvia.) I have some darker slides with look ok on a light table, but just turn to muddy mess when scanned. I've tried multi-exposure, but just still can't seem to get there with my equipment. I think, if the image is worthy, those are likely good candidates for a professional Flextight or drum scan.

I agree, dark slides suck when scanned. Almost impossible to pull them up. I am going to go ahead and perchase a target and take some shots and create some profiles for different slide film. I scan at 3200dpi (easy division for using with Canon iPF6400 printer. Could go up to 3800dpi. At 4K file was 1.8gb in size, I can only imagine the size and time for a 6400dpi scan, even if down sampling. I prefer though not to down size and just scan at the native resolution I want for the master file.

[Ted Baker]

Okay, that makes sense. There is no color space assigned to the raw file so I do that in PS.

Yes but what colorspace would you assign?

Ideally you would calibrate your scanner for the spectral response of the material your scanning, then would know what the raw values in your files are in CIE XYZ colorspace, which you can use to transform to any other colorspace like sRGB.

However in the case of viewscan, when you save anything other than RAW, it is supposed to use a generic transparency profile, i.e. use matrix algebra to transform the raw values into the correct values for the chosen colorspace, the default being sRGB.