First photos and image editing

Starting out in microscopy? Post images and ask questions relating to the microscope and get answers from our more advanced users on the subject.

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cordyceps
Posts: 11
Joined: Thu Apr 11, 2019 7:00 am

Re: First photos and image editing

Post by cordyceps »

Thank you Rik!
I have another question, when opening a photo in GIMP I have to choose if I want to convert the image to the RGB working space and If I do, what type of rendering intent I want. When I want to manipulate with colors I think it is better to convert the image, but what type of rendering intent should I choose?
Image
I fount this article: https://www.cambridgeincolour.com/tutor ... ersion.htm
RECOMMENDATIONS

So which is the best rendering intent for digital photography? In general, perceptual and relative colorimetric are best suited for photography because they aim to preserve the same visual appearance as the original.

The decision about when to use each of these depends on image content and the intended purpose. Images with intense colors (such as bright sunsets or well-lit floral arrangements) will preserve more of their color gradation in extreme colors using perceptual intent. On the other hand, this may come at the expense of compressing or dulling more moderate colors. Images with more subtle tones (such as some portraits) often stand to benefit more from the increased accuracy of relative colorimetric (assuming no colors are placed within the gamut mismatch region). Perceptual intent is overall the safest bet for general and batch use, unless you know specifics about each image.
Most of my images does not have intense colors, specially before edition, so I would choose to go with relative colorimetric. If I will edit some photo with intense colors, I will then use perceptual. Is it okay to start with? If you have some thoughts about this, please let me know.
rjlittlefield wrote:
Sat Aug 15, 2020 5:25 pm
Here are images that I corrected by levels adjustment in Photoshop. The way I do this is to add an adjustment layer, bring up a histogram, focus my attention on the three peaks that represent background color (which is almost everything here), then separately adjust the upper limit of two R/G/B bands so as to move the left two peaks over to match the right. Notice that in the uncorrected version there are three clearly separated peaks, one each R, G, B, but in the corrected version there's only a single peak.

I see that I also brightened the image when I color-corrected it. That's because cameras' metering expects the scene to average 20% gray, so brightfield microscopy images that are "properly" exposed according to the camera are routinely too dark.
I tried to follow your steps and here is what I achieved.
Before color adjustment:
Image
After:
Image
For sure it looks closer to yours, but still something is off. Your corrected image seems brighter and less bluish. Do you have any idea what am I doing wrong?
Also I found out, that I can do this level adjusments automatically, by picking a tool called "Pick tray point for all channels", clicking on a background and it does the same thing, which is adjusting colors that RGB is a single pick on histogram.
Color adjustment by "Pick grey point".
Image

cordyceps
Posts: 11
Joined: Thu Apr 11, 2019 7:00 am

Re: First photos and image editing

Post by cordyceps »

This tool also allows me to adjust colors in some other pictures, where there aren't three separated picks of RGB and I have no idea to to adjust them manually. (For this photo I picked perceptual for rendering intent.
This is a stack of 15 photos of some algaes. As you can see, RBG histogram is far from the last one.
Image
After edition with "Pick grey point".
Image
This picture has uneven illumination, the bottom part is darker then the upper part. I don't know what is the cause of it. Maybe it has something to do with my homemade camera connection, it is another issue I will try to improve.

rjlittlefield
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Re: First photos and image editing

Post by rjlittlefield »

cordyceps wrote:
Wed Aug 19, 2020 4:37 am
I have another question, when opening a photo in GIMP I have to choose if I want to convert the image to the RGB working space and If I do, what type of rendering intent I want. When I want to manipulate with colors I think it is better to convert the image, but what type of rendering intent should I choose?
...
Most of my images does not have intense colors, specially before edition, so I would choose to go with relative colorimetric. If I will edit some photo with intense colors, I will then use perceptual. Is it okay to start with? If you have some thoughts about this, please let me know.
That seems reasonable to me.
I tried to follow your steps and here is what I achieved.
...
For sure it looks closer to yours, but still something is off. Your corrected image seems brighter and less bluish. Do you have any idea what am I doing wrong?
Mine is definitely brighter. As I mentioned, "I see that I also brightened the image when I color-corrected it." That was something I did manually, by adjusting levels for all three channels instead of just the bottom two. I agree that yours looks a little more bluish, but that's probably just a slight difference in where you put the sliders.
Also I found out, that I can do this level adjusments automatically, by picking a tool called "Pick tray point for all channels", clicking on a background and it does the same thing, which is adjusting colors that RGB is a single pick on histogram.
Color adjustment by "Pick grey point".
Picking a gray point is always worth a shot. Sometimes it works great; sometimes it doesn't. The difference between great and not-so-great depends on exactly where you happen to click. The tool will reliably turn the point that you pick into gray, while changing all other colors accordingly. But I usually find that there are subtle color variations in my images, with the result that I have trouble finding a spot which when turned gray, has the effect that I want everywhere else too.

An even better approach, which I should have mentioned at the beginning, is to set color balance correctly in your camera, so that you don't have to make big changes after the shoot. If you were shooting raw this would not matter because you could do the appropriate balance in raw conversion. But when you're shooting JPEG or TIFF, the camera is doing the conversion from raw for you, and it's leaving the result in a format that is hard to make further big changes with. It's much better if JPEG and TIFF are close to correct colors when they come out of the camera.

So, you should definitely read the manual for your camera and learn how to set custom color balance (likely called "white balance"). Then get in the habit of setting or at least checking white balance periodically with a blank slide. That will automatically make clear areas neutral, which will make all the other colors look better also.

Be aware that when you change brightness on your microscope, the color balance may change also. If it's using an incandescent bulb then the colors will change a lot. If LED, then not so much but maybe still enough to matter. Check to be sure.

--Rik

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