Switching Profiles Non-Destructively and RGB to Grey Conversions

[Frank Petronio]

If I merely open a PSD file and "assign" or "convert" a different color profile to the image in order to print it without making any other moves, am I making an image destructive move?

And....

If I have a nice Adobe RGB tagged RGB PSD file and assign/convert/use a greyscale profile, such as "Gamma 2.2" and print to my Epson, is the Epson seeing my image as a greyscale image and doing it's own color conversion? It seems to work in a casual test, but I wonder if anyone does this as a matter of course?

[Greg Miller]

Assigning a new profile does is not destructive. No pixels change; the only thing that changes is how any given software (e.g. Photoshop) interprets the numbers.

Converting to a new profile is destructive. Numeric values for each pixel actually change to the closest value available (rendering intent has a role in this) in the new profile. In 8 bit miode this could cause a visual difference in your image but converting once in 16 bit mode is unlikely to cause change that you can see. You should be careful though in switching from a wide gamut profile, such as ProPhoto RGB, to a narrow Gamut profile, such as sRGB. It is possible to get banding as several neighboring pixels who had different values in the wide gamut profile get forced to the same values in the narrow gamut profile.

An Epson printer is an RGB device. SO if you send a greyscale image to it, the greyscale values must be converted to RGB values, which would be destrctive (although maybe not perceptible).

[Greg Lockrey]

This may be out of place to suggest, but why don't you just do a "save as" to protect the original file?

[Frank Petronio]

The reason I ask is I'm wondering if I can avoid having to to do hundreds of "save as"s!

[Jeffrey Sipress]

I've never needed to change the colorspace of my working document to make a print. I work in Pro Photo RGB (I think it's called that!) and never change it except within my save for web action. Even if you do, just do it before print and leave the original saved as is.

[Marko]

Why don't you just convert to B&W within the Adobe RGB using, say Channel Mixer or B&W Conversion, both in the form of adjustment layers (or even a combination)? That way, you can safely save your file without much size increase and without loosing anything and if your space is set up right, you don't need to convert to another space for printing either, ICC will take care of everything.

[Richard M. Coda]

On the RGB to Grey conversions... I have always found it better to utilize several techniques rather than rely on the Photoshop convert to grayscale. The new photo filters are nice, but doing it by hand is much better.

I have made available a lo-res PSD file of an image that started out as a DSLR capture (it's all I had at the time) and made a grayscale file that I then had output to a silver negative that I now print in the darkroom.

Open up the PSD and uncheck all the layers except the Background, then add them back one at a time starting at the bottom. Once you have the final image, you can flatten and convert to grayscale mode with no loss in quality.

File here

[FilmIsNotDead]

Just add a couple of adjustment layers : first layer is original image, second layer is hue/sat with sat all the way down, third layer is curves (or similar). Save as a PSD with the new layers which can be readjusted and saved anytime you like non-destructively. One nice thing about doing it this way is you have some control to darken/lighten specific color ranges via hue/sat.

[rdenney]

For converting to grayscale, I have found that the Channel Mixer (with the monochrome box checked) provides the greatest control. With my new Epson 3800 printer, I've been getting results that please me using the Advanced Black-and-White mode, which gives me a way to add a toning effect in the printer driver, and expects to see grayscale coming in. It will convert an RGB image coming in to grayscale (and then back to RGB as part of the printing process), and that will have no effect as long as R=B=G in all pixels. That will be true with the Channel Mixer. I've tried the black-and-white adjustment layer in CS4, and it seems to do basically the same thing.

I have many images stored in the sRGB color space, and many more in the Adobe1998 color space. This was fine for me until I got this new printer--it has a wider gamut than sRGB and I didn't want to give it up. So, I've been converting these files to the ProPhoto colorspace as needed. I have found that the conversion will usually leave a bit more room at the ends of the histogram than I had before (easily corrected using curves), and I've certainly never noticed any ill effects. In fact, I've often been able to cure a problem of running out of gamut when I wanted to adjust the curves to suit my visualization. And both my Epson and Nikon scanners, when scanning Velvia, seem to be able to fit the whole dynamic range of the scan into the ProPhoto or Adobe 1998 colorspace more easily than in sRGB.

Converting a wider gamut to a narrower gamut will force some color values that had been different to become equal, which causes a loss of tonal separation information in the file. I only do this when converting to 8-bit JPEG for web display, however, and that does make a significant difference in the look of the print. When targeting a file for web display, I save a copy and then turn on the proof colors using Windows RGB (which is essentially sRGB) and then correct the image so that it looks okay. Then, I can "save for web" without changing the look unacceptably. That never enters into my workflow for print targeting, however.

I always work in 16-bit (color or grayscale), converting to 8-bit JPEG files only for web display. I send those 16-bit files to the printer with no problems I've noticed, even though I don't have a 16-bit RIP. The Epson driver is making the conversion, and so far I have no complaints with what it does.

Rick "JWID" Denney

[Lenny Eiger]

I like the channel mixer best. PhotoShop's conversion strategy is something like 60-69% red channel, the rest blue and green if you look at the channels, that's not what you want. The red is almost always the noisiest. I don't want to let PhotoShop choose this. If you desat, that's what it will do, if you use the b&w conversion thing, that's what it will do.

The adjustments that a conversion will do are easily done with a curve adjustment, same with sat. And more properly done that way, IMO.

Lenny