I have been having a problem with bright blue pixels showing up in some of my scans. They are most visible in light areas, such as clouds, and seem to aggregate in transition zones. The blue pixels do not appear until I make adjustments in the black and white points. Strangely, they seem to shift and redistribute themselve as I adjust levels or saturation. I have not yet tried to make a print from one of these scans, so I don’t know if they would appear there as well.
Is this a problem with Photoshop, the scanner or the monitor? Or is it simply a nuisance that I will have to accept?
As mentioned, I have not yet tried to print one of these images, which is something that I need to do soon. My computer has about 1.8Gbytes of RAM, so I doubt that is the problem. When I save/close/reopen, the blue pixels are still there. I have not yet tried to open one of these files on another computer.
When Neil mentioned RAM, he was referring to possibly bad RAM (if the artifacts print). The other possibility is a bad video card (if they don’t print).
Major discovery, I think. My usual color working space is Adobe RGB (1998). When I convert to sRGB, the blue pixels disappear. Does this ring any bells for anyone?
Could be several things, foremost among them a sign that it may indeed be a Video Display Card problem. The change of color space would be substantial enough to cause a major refresh. RAM in this case would be less likely, though not impossible.
Also, if the blue pixels happen to be within the gamut of Adobe RGB but out of the sRGB gamut, they’d be compressed or clipped during the conversion, but I’m just speculating.
Use the brush or pen tool and draw circles around the dots when they appear. Then resize the image by 10%. Are the dots still within the circles? If not, it’s your video card RAM. Otherwise, it’s your system RAM, or possibly the color space. (But most likely RAM) I have seen this a lot.
Another test is to try to measure the value if the blue pixels with the color eyedropper. If the numbers don’t come up 0 0 256 (or whatever) then it’s the video card.
With a bad video card, the pixels tend to float about on screen when moused over or if the image magnification is changed, and they don’t print.
I doubt if it’s the color space. If you exceed the gamut for the color space, the colors become less saturated or shift to a different color. They may become less prominent. But, AFAIK, the aberrant pixels don’t just disappear with a change in color space. And they certainly wouldn’t float about.
I tried your experiment. For the most part, the blue pixels moved out of the circles when I resized the image. According to your theory, this means that I have a bad video RAM card. Is there any other way to test this conclusion before I replace the card? FWIW, I have never noticed any other aberrations with my monitor, but ordinary use is probably less demanding than Photoshop. By the way, what exactly is involved in replacing a video RAM card?
Well, if was me, I would consider the experiment concluded. But if you want to be sure, view the image on another computer, or upload it to the web and ask a friend to look at it.
I am pretty sure Photoshop uses the card’s LUTs more than most other software, so it does not surprise me a bit that you only see it there.
The possibility remains that it’s your system RAM (though I would swap the video card first) so don’t buy an expensive video card yet. If you are just using Photoshop, you can get away with a less expensive card- all the polygon generators and pixel shaders in the new expensive cards are not necessary for Photoshop.
the other easy tests were already mentioned: how the suspect file prints or how it looks on another computer. PLEASE do that and report back before buying anything.
To replace the card (instructions are included), you generally do nothing more than turn off and disconnect your computer from the electric outlet. Disconnect the monitor’s signal cable from the video port. Open the computer’s case. Ground yourself on the power supply and wear a grounding strap on your wrist (straps are very cheap but can save you from frying expensive internal components with accidental static electric discharge.) Hold the old video card by the edges only and gently rock it out of its slot. Do not flex the card in the process.
Insert the new video card by reversing the steps. You will have some resistance in inserting the new card. But, DO NOT USE EXCESSIVE FORCE to insert and properly seat the new card. And make sure that the card is evenly inserted into the slot.
If you are uncomfortable fiddling around inside your computer, let a qualified repair shop install it. It shouldn’t take more than a couple of minutes.
If there is software with your new video card, install it as instructed. But the most you will probably have to do is recenter and resize the desktop image and select the proper screen resolution. Then you should redo your monitor’s color calibration.
I’ll burn a CD today and open the image on my computer at work tomorrow.
Any idea what a new video card costs? Any recommendations for a particular card? As you have probably guessed, I’m not very computer savy. But I do love photography, and I have only recently begun to learn the wonders of Photoshop.
Update on the blue pixel problem: I opened an image that exhibited the problem on my home computer on two other compters today. The result–no blue pixels. This would seem to clinch the idea that the problem lies with my video card. I’ll start looking around for a replacement. Any suggestions will be appreciated.
I just ordered the ATI Radeon 9000 for Mac. It sounds like a major upgrade over the card that came with my computer. I’ll post a follow-up once I get it installed.
