Astroimage processing

Re: Digital images and computer screens

jballauer — Wed, 27 Aug 2008 00:17:49 GMT

Perfect! Thanks for the contribution!

Re: Digital images and computer screens

TeleNoob — Tue, 26 Aug 2008 19:04:17 GMT

For anyone who cares, here is what I have done for color management. First thing was, to obtain a test pattern image that shows 256 shades of grey, such as this one-

Which I use to adjust my contrast and brightness. The bottom left corner is RGB 0,0,0 while the top corner is RGB 255,255,255. All other steps are displayed in-between.

But I also wanted to look at the response of my monitor to varying colors. So the next step is I made 3 new images out of this one, one each in the Red, Green and Blue. Eg- the red image is RGB X,0,0 where X goes from 0-255. By looking at these images one at a time I can make adjustments in my video control panel. This allows me to adjust the Gamma, Brightness and Contrast of the three color channels independently. I found that all 3 channels needed a slight gamma adjustment to allow me to see as much of the 256 shades as possible. The adjustments were not exactly identical, but pretty close. The actual hue of the colors is not adjustable in my control panel. But with this method I can at least optimize the channels for best range of colors displayed.

My overall impression is that the adjustment has made my laptop screen colors more vibrant. As a result, images I make in the future may now have slightly less color saturation than before.

Re: Digital images and computer screens

TeleNoob — Mon, 18 Aug 2008 18:09:11 GMT

I take back what I said, my interest would be actually more in the scientific. I want to do imaging to see details, features that cant be otherwise seen, purely out of scientific interest. The actual color of the planets disk might not be "true" in some cases, but doesn't matter so much. I would sacrifice color correctness, before losing detail. Sometimes other colors can even help bring out the detail, the so-called false colors.

So it is definitely true that I am more interested in acquiring knowledge, about Jupiter or about Saturn or what have you. than a totaly perfect image.

Still, I think monitor calibration helps this aspect too, in seeing more details. For example, if your red channel is too high on the screen, it might saturate before the data in the image reaches 255. If you were looking at a red image you might lose detail in bright areas. But if you calibrate the red it better matches the range on the image data, so it might show more details.

My Laptop has an allowance for changing the gamma of the RGB channels independently. I might try and obtain a set of reference color cards, see what results I get, how much change it requirs on different types of monitors. Highly subjective work this way perhaps, but the cards do seem to have the benefit, of taking into account the background lighting in the room your in, somthing which the sensor might not do. (?)

Re: Digital images and computer screens

galactic_photog — Mon, 18 Aug 2008 14:38:10 GMT

I find that monitor calibration allows me to experience a closer match of the various shades of image colors, between the four monitors that I use (2 CRTs, 2 LCDs),when viewing photos in both fully, and partially managed environments (such as those photos, passed via disc, and opened for viewing in photoshop, w/o resorting to the eyedropper, and viewing photos posted on my website on the various monitors).

I suppose that in order to close out this discussion, it would be appropriate for us to agree to disagree on the value of color managing.

Robert

Re: Digital images and computer screens

jballauer — Mon, 18 Aug 2008 02:11:56 GMT

There is no cost excuse for not implementing full color mangaement. There are only missinterpreted colors,...and green backgrounds...

This is my point. Once you understand what you are doing, you'll be able to detect color bias simply by looking at the data points in Photoshop. If your background is 10:25:15 RGB according to the info cursor, then you've got a green cast. If it's 0:0:0 RGB, then you've clipped the blackpoint and you've lost data. If it's 25:25:25 RGB, then you've got a nice neutral background. If you perform a saturation increase and the histogram shifts away from the other color histos, then your balance will be wrong.

Therefore, I don't look at a lot of monitors and wonder "which one is right?"

Re: Digital images and computer screens

jballauer — Mon, 18 Aug 2008 02:05:14 GMT

Robert:

I appreciate what you are saying, I truly do...and I don't totally disagree. I just think it's one of those things that's that comes a little later...for most hobbyists, it can take years to generate images of such quality that you'd be concerned about consistency from monitor to monitor. For me, it wasn't really a concern until I started putting my work into print, at which point I got picky about color management. But even then, I tended to trust my tools and didn't allow what I saw on the screen to dictate what I did with an image.

I agree that, in time, even the hobbyist can and SHOULD seek to learn the benefits of proper color management, particularly if your goal is to take your images to print. I also don't mind it from the standpoint that a.) if you are technically savvy and are quick to understand and b.) you've already nailed down the million other variables that make for good images.

Like I said earlier, there are several things you can do to calibrate a monitor so that you can see authorial intent...and no matter what monitor I'm on, it's never kept me from understanding what an author is trying to do...as I've given a lot of advice over the years to a LOT of people. In my opinion, using hardware calibration tools just isn't a necessity in this hobby.

Re: Digital images and computer screens

chipdatajeffB — Sun, 17 Aug 2008 21:38:50 GMT

Yes, most newer monitors have built in calibration software, and test strips that allow the user's eye to perform the calibration "sensor" function.

I like to be VERY careful when using the word most. I don't think it applies here, nor do I think it would be easy to determine when this will be true. What percentage of the monitors sold today are entry-level quality? I think this percentage is very high. The mass-market is what it is, and it's not great. But, again, how do you determine this ... and who determines it?

But that's not the point: I think it's easier to guess that most monitors today are not newer models. I own four monitors, not one of which is newer than 4 years old. Am I average? I don't know, but I find it a stretch to believe that the average user has a monitor with this capability built in. It might be true now. It is more likely to be true as time goes on.

Re: Digital images and computer screens

galactic_photog — Sun, 17 Aug 2008 20:45:40 GMT

tkerr:
I think this thread has taken a new direction and has been somewhat hijacked

Absolutely

tkerr:
That diverseness of the members and their opinions can most often be very helpful,

Both sides of a discussion, pro and con, regardless of the personal opinions of (any) individual members should be aired, in a civil fashion, for exactly this reason. As close as possible to full disclosure of those pros and cons will allow readers to decide for themselves, whether it's worth any effort to further pursue.

(I'm not loosing any sleep over my monitors being a couple to several months out of calibration.)

Robert

Re: Digital images and computer screens

tkerr — Sun, 17 Aug 2008 20:27:07 GMT

galactic_photog:

I saw another post on this form, were the poster commented that he was using a very expensive (five figure) camera. Assuming a good concept of system balance, I suspect that the rest of his astrophoto setup (focuser, rotator, OAG, scope, mount, guidecam, dome, controller) cost four or five times this amount. He will undoubtedly spend significant time, in at least a couple expensive processing programs before he moves to final processing, in a color managed program like Photoshop, itself an expensive program. He will spend hours (?) finalizing his photo in Photoshop. At this point, he looses any control over the color, as viewed in his photo, by someone else, in their non-color managed web browser, using their own, uncalibrated monitor. I expect that the difference, for most people viewing this image on the web, using a monitor in whatever state, is small (see my above comment concerning actual vs rendered colors of astronomical subjects).

Might I point out here, Once again, this is a minority of the members here at "astronomy.com forums". The overall majority "DO NOT" have equipment that cost them 5 figures. The opposite might hold true at some place else but not here. Please, let's all consider the majority of astronomy.com members who might be reading these discussion threads.
I think this thread has taken a new direction and has been somewhat hijacked. Differences in a persons experience and their opinions are expected in these forums. That diverseness of the members and their opinions can most often be very helpful, however, I think there comes a point when enough is enough. We're not here to scare anyone away.

Have A Nice ___________

Re: Digital images and computer screens

galactic_photog — Sun, 17 Aug 2008 20:24:08 GMT

TeleNoob:
It depends on if that level of accuracy is needed by the user. Some remote viewing stations don't need the extra fine tuning, the factory defaults are good enough. But as someone pointed out, if it is inexpensive to do, why not do it then.

Yes

TeleNoob:
I've seen some systems that come with these colored paper cards, that I presume are held up to the screen and compared, subjectively to a reference image. That might be good enough for me, as I too am only trying to take pretty pictures! Does anybody here use those?

Yes, most newer monitors have built in calibration software, and test strips that allow the user's eye to perform the calibration "sensor" function. That approach is better than nothing, probably gets you 80 or 90% of the way there, if you have "normal" color vision. You will need to keep the lighting consistent, both level and temperature (differing standards on this, but generally around 5000 deg. K if you want to adhere to a norm).

If the cost of a sensor and associated software represents a significant fraction of your total system costs, it is probably a better value to just use the cards. If you're using an expensive system, then that sensor will be pocket change (and the hassle of calibrating once, or twice per month, and maintaining a consistent level and color of lighting should be acceptable).

Robert

Re: Digital images and computer screens

galactic_photog — Sun, 17 Aug 2008 19:22:48 GMT

chipdatajeffB:
Quite true for digital photography magazines. I haven't seen it discussed to any real extent in astrophotography publications

The concept of color management has been so thouroughly covered in the conventional photography community, that essentially all intermediate or advanced aamateur photographers are, at least familar with the concept, what it offers, and even a few methods for accomplishing it. The topic has had very little discussion in the astrophotography community. A few of the participants are aware of it (generally the few that are also conventioanl photographers or those associated professionally with graphics and printing).

chipdatajeffB:
if the astrophotographer captures white as white, and black as black, and does not apply any significant gamma correction, then he's done the best his camera is capable of capturing. If he does not then follow that process by altering color in post-processing, then he's produced a "neutral" image,

This is may be close, for the photo that the originator produces, but is only the beginning if that image is passed to another person for viewing on his monitor, especially if over the web.This comes down to how much benefit, how much cost, and how much do you care about it.

I saw another post on this form, were the poster commented that he was using a very expensive (five figure) camera. Assuming a good concept of system balance, I suspect that the rest of his astrophoto setup (focuser, rotator, OAG, scope, mount, guidecam, dome, controller) cost four or five times this amount. He will undoubtedly spend significant time, in at least a couple expensive processing programs before he moves to final processing, in a color managed program like Photoshop, itself an expensive program. He will spend hours (?) finalizing his photo in Photoshop. At this point, he looses any control over the color, as viewed in his photo, by someone else, in their non-color managed web browser, using their own, uncalibrated monitor. I expect that the difference, for most people viewing this image on the web, using a monitor in whatever state, is small (see my above comment concerning actual vs rendered colors of astronomical subjects).

If the expense of color management was high, I'd agree that it would only be applicable to a very small crowd, in restricted cases, but this is not the situation. The color management cost, and effort, is a tiny component of the high expense that the imager has gone to in exposing and processing his image. There is no good reason to ignore it.

Robert

Re: Digital images and computer screens

chipdatajeffB — Sun, 17 Aug 2008 18:16:36 GMT

galactic_photog:

chipdatajeffB:

It may not be as important in digital astrophotography if the originator's intent is simply a pretty picture.

Maybe, maybe not. The originator may select a neutral sky color in photoshop

Note the word "astrophotography" in my quote ...

Why leave additional uncertainties in the system, when there are perfectly good, cost effective, solutions? ... If you happen to subscribe to any of the various amateur ( or professional) photo mags, both sides of this discussion were played out over the last several years. ...

Quite true for digital photography magazines. I haven't seen it discussed to any real extent in astrophotography publications. What would be helpful in that regard would be a discussion about what this means to the astrophotographer. I go back to my "close enough is good enough" argument: if the astrophotographer captures white as white, and black as black, and does not apply any significant gamma correction, then he's done the best his camera is capable of capturing. If he does not then follow that process by altering color in post-processing, then he's produced a "neutral" image, insofar as he can.

Now, if the astrophotographer wants to publish his work via the Web, he must either accept that the vast majority of screens on which his work will appear are "close enough" to display his image in a way that suits him or he must go the extra mile and provide the color-matching data.

My argument is that most of us (I know several astrophotographers, not one of whom uses color-matching techniques, to my knowledge -- they certainly don't talk about it anyway) do not care to go this extra mile. So, if there is an article that shows a measureable difference between what we're capturing using our standard methods and some "standard" we should be expected to meet, then that would be helpful. I'm not aware of such an article, but would certainly read it if someone could supply a link.

A new point: I readily confess to being largely color-blind. I see colors, but I don't see them correctly. Therefore, I rely on my image-capture software and stacking/processing software to help me "correct" the color balance in my images. I am therefore probably a good "test-case" for whether, and why, color-matching software and techniques are helpful.

Here's an example to illustrate my point:

The image on the left is color-wise directly as it came from the camera. I used an FL-D (light magenta) filter to enhance surface detail. This skewed the color balance of the camera, which was set for Outdoor (daylight). The FL-D filter blocks green, primarily. I see this image as brown. I actually displayed it against a pantone color chart and matched it to brown. It is not, however, brown at all. So, strike one for visual color balance and match for me (since I'm color-blind).

To color-balance the image on the right (which by the way is exactly the same image from a capture standpoint), I displayed the RGB color histograms and moved them until I had applied enough correction to zero out the differences in brightness of each color (matched them all to the same brightness), then I applied a gamma adjustment (slight S-curve shape, like an integral sign) that altered the overall balance to offset the characteristics of the camera Bayer filter.

A slight histogram stretch (just a few percent) enhanced contrast just a bit.

Which image is more scientific? The one on the left, since it is altered in a known way which could be repeated exactly by anyone using the same equipment. Which is a "better" image? I maintain it's the one on the right. That image already has been used by a professional astronomer who studies the seasonal changes in the North Polar Hood (the blue area at top and left). I sent him both images, by the way.

In my Flickr! albums, the image on the left has been viewed by 1,507 different people, while the image on the right has been viewed by 2,488 -- for whatever that's worth.

Neither image has had the sort of color-matching you're advocating applied. In my opinion, all that would buy me is that once I'd reprocessed the image using a calibrated system is an image that someone else could view exactly as it would display on my own system.

I suggest that very few people actually have the color-matching technology. I further suggest that if the "average" monitor is so far off the mark that it would significantly detract from my image, then most of us are buying very poor monitors.

What I'm wondering is that if I did the monitor calibration, and then reprocessed my image, how much difference would there be between the histograms and RGB values of the before/after images? If the answer is very large, I'd be surprised (but it's possible I suppose). If the answer is very little, then I don't see how it would matter to me or the majority of folks who view my images. I'm not arguing here that there would be zero difference ... I'm just suggesting the difference would be so small as to not be "valuable" (to me, or the vast majority of viewers).

Re: Digital images and computer screens

tkerr — Sun, 17 Aug 2008 17:59:51 GMT

Can of worms, Nope, Perhaps a couple!

I like pretty pictures too. I'm not here to analyze every celestial object captured in an image. I'm not learning astrophotography for that purpose either. I just do it because I can, and the fact that I can is amazing.. I do it because It is something I enjoy as a pastime. If I ever lose that enjoyment, and it starts to seem too much like a job, then I will probably quit.

I have used those color cards in the past. With my older CRT monitor, But with my new one I don't need that.

About that can of worms.

First of all "everyone" must remember we are a group of amateur enthusiasts just here to enjoy ourselves and share whatever, and within our personal limits, possibly gain a little more knowledge. We are not a group of professionals here.
I can't speak for everyone else, but I prefer to learn how work with and be more proficient with what I have without going out spending all kinds of money on professional equipment. It would be different if my career choice required it, but it wasn't my choice and it's not necessary here.

Secondly, It won't matter what the intent of the person posting the image really is. If he or she wanted their images to look the same on every monitor it is viewed on throughout the World Wide Web, then everyone logging onto the Network viewing the image would have to have their monitors calibrated the same. Let's get realistic here, That just isn't going to happen.

For all practical purposes the following is the best advice for the overall majority here on the Internet.

jballauer:

Just be sure that your whites are whites and your blacks are blacks when it comes to color balance and temperature. Use a brightness scale to adjust your monitor brightness (http://www.cosmotography.com/images/calibrate.html).

With that said. What is the best lighting to have. Fluorescent, Incandescent or what?
I personally prefer fluorescent and that is what I have at my desk. It is a more natural light where the standard household incandescent bulb gives off a slight yellowish tint. There are also times I prefer no light.

Have A Nice ____________

Re: Digital images and computer screens

TeleNoob — Sun, 17 Aug 2008 17:02:51 GMT

My intent is to learn what the issues are, and what tools there are available, from people who might already know. As I said I work in medical imaging and this is something that we deal with as well, but its not implemented in all areas. It depends on if that level of accuracy is needed by the user. Some remote viewing stations don't need the extra fine tuning, the factory defaults are good enough. But as someone pointed out, if it is inexpensive to do, why not do it then.

I think certainly if we are going to be the originators of an image, those systems should be checked and calibrated, because that will be the original source of the data file. So far I have learned that my brightness was too low, by the gray scale map and now I have a few bitmaps saved in my folder, which I will check now and then before doing image editing.

Even the background lighting of the room I'm in makes a difference, I understand that and some medical monitors do have an ambient light sensor, they increase the brightness/ or decrease it when the room lighting changes.

I am all for calibrating the monitor and looking for inexpensive tools to help me do it. I've seen some systems that come with these colored paper cards, that I presume are held up to the screen and compared, subjectively to a reference image. That might be good enough for me, as I too am only trying to take pretty pictures! Does anybody here use those?

Thanks for your feedback :)

Re: Digital images and computer screens

galactic_photog — Sun, 17 Aug 2008 16:49:23 GMT

chipdatajeffB:

Well, maybe. But how do you know the originator's intent?

The intent of monitor/photo file/file transmission color management is to allow the remote image viewer, using his monitor, to view the same shade of blue (green, or whatever) choosen by the image originator, implemented in his photo, and seen by him on his monitor. If implemented, ideally, this would allow the remote viewer to see the photo just as if that viewer were standing in the same room with the originator, looking over his shoulder. The variations pointed out earlier preclude this from being absolute, but only through color management can the differences be minimized. If the originator implemented a shade of color different than what he truely intended, that's his problem.

chipdatajeffB:

It may not be as important in digital astrophotography if the originator's intent is simply a pretty picture.

Maybe, maybe not. The originator may select a neutral sky color in photoshop (or other color managed image processing software), but the remote viewers sees a green cast sky, because his monitor/web browser accenuates the green component of what was a neutral sky. Had both been using full color management throughout the image creation, web or ftp transmission, and remote viewing, there would have been a reduced chance of this (see above disclaimer).

chipdatajeffB:
But if your intent is to produce pretty pictures, you generally run into the "how close is close enough?" question and for most "pretty picture" purposes, it seems viewers are quite happy with the typical browsers and monitors which are uncalibrated.

Why leave additional uncertainties in the system, when there are perfectly good, cost effective, solutions? Thousands are spent on each component we use in order to get that pretty picture. A few hundred more dollars, and a little time each week, can reduce the missinterpretation to our intent, or more accurately to what we implement in the photo.

If you happen to subscribe to any of the various amateur ( or professional) photo mags, both sides of this discussion were played out over the last several years. It would be best to review their archives for unending pro, con, costs, benefits discussions.

Robert