Auto levels, auto contrast, use with caution...
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#1. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 0
flashdeadline Registered since 07th Apr 2002Wed 02-Oct-02 04:12 PMBJ
Now ya done torqued me off.
Three shots posted-- each with explanations. But no example of the best way.
The reason I'm torqued is I downloaded your original, and spent half an hour trying to get it to look right, using curves and levels.
I failed--- very badly.
A lot has to do with no real reference frame as a shooter (is that white snow in the foreground-- so can I go with the known standard for white?--- is there anything really "black" in this picture?)--
This has been a real brain twister for me-- and I'd love to see your fix--
---Tom
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
---Tom
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
"Nikonians membership - My most important photographic investment, after the camera."-
#3. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 1
If you are going for accuracy to the transparency and the scene as it was shot, the first image is correct, no fix needed. You have the same difficulty that Photoshop has with the auto corrections stuff, you can't see the slide and you weren't there when the shot was taken.
The point is that not every image has white or black. This was shot on a foggy day with low contrast and subtle color. Adjusting the histogram for a true black and a white-white is wrong for this image. Photoshop screws up because it automatically moves to give you the histogram endpoints. There are a lot of images that don't have the full range of values and colors, so if you turn automation loose on them, you'll wind up with something you didn't shoot.
This example isn't done to argue about what the most pleasing treatment of the image is. I like the foggy scene as it was shot, so that's the way I edited the scan. Creative adjustment is a different subject altogether. If you want to modify an image creatively, that's great but you wouldn't rely on auto curves or levels to make that kind of change to the image. Or at least you shouldn't, since either auto process provides only one alternative to the original image from the myriad of variations you could choose.
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#2. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 0
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"RE: Auto levels, auto contrast, use with caution..."
danshep Charter MemberWed 16-Jan-08 10:10 AMEverybody's gotta play. Me too.
Here is what I did. Downloaded the image, then created a levels layer. I made a guess, by looking at the histogram that the black began around 48. I left the white alone at 255.
Then I created an adjustment layer for THRESHOLD. If you slide this all the way to the left, you get no image at all. As you slide it to the right, the darkest spots begin to appear. This is how you discover your black value. You use the eyedropper and find out what the number is. In this case, I got 41. I hit OK and then opened the LEVELS layer and changed the dark value to 41. Then I went back to the threshold and slid it all the way right. Total blowout. Then as you slide it to the left, you get the whitest spot. I used the eyedropper to find the value. It said 230, so I lowered from 255 to 230.
Then I created a layer for brightness/contrast. Although this is subjective, I increased brightness 10% and contrast 10%.
Regardless, even if you throw out the brightness/contrast layer and leave it, you have a much improved photo.
Oh, yeah. I used unsharpen mask and set it at 100, .5, 1.
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"Today is the tomorrow that yesterday you spent money like there was no."
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#4. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 0
Again, a pleasing interpretation of the image, but not true to the subject or the slide. You prove my point, however. By manually working on the image to get something you find pleasing, you have far more control of the end result.
You're wrong about "discovering" the black value. There is not a black value on this image unless you make one as you did. The fog mutes the tones so there really wasn't a black or a white in the scene. Don't treat every image as if it requires a full range of tones from 0-255 or you'll become the human equivalent of Photoshop automation.
And although I don't mind your interpretation, I like the original photo better. It communicates the softness and mood of the day, yours doesn't. This should be a lesson to folks shooting film negs where there isn't a reference to work from. Even if you have an expert lab technician make you a custom enlargement, that person can easily put their own spin on the resulting print, just as in this Photoshop adjustment. You may like the result, you may not.
The reason I do my own digital darkroom work is to maintain creative control from scan to print. If you lean on automation without thinking about the effect on your image, you lose out on the biggest benefit the process opens up for you.
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#5. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 0
Thank you for posting good examples. I thought there is something intelligent behind autolevels but it seems to be just an ordinary histogram stretch, although I suspect there might be little bit better algorithm for finding low and high end values than usual 0.05% clip. Auto contrast seemed also to be just black level shift but surely "Auto Contrast" sounds much better
Janne
#6. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 0
I picked up some great pointers from Dan in his post as well.
I must admit I'm more likely to seek the Dan version in my line of work, only because I know once your original gets the CMYK newsprint at 2 in the morning treatment it will automatically get worse---
On the other hand, the extra spark in Dan's version will be "dumbed down" through that same process and end up looking more like your original.
Now, if your original transparency was to be headed for National Geographic--- that's another story.
Please keep bringing these lessons to us-- no matter how much you frustrated me I was still engrossed, and educated by your post.
---Tom
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
---Tom
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
"Nikonians membership - My most important photographic investment, after the camera."
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#7. "RE: Auto levels, auto contrast, use with caution..." | In response to Reply # 6
You need to adjust an image for offset printing with unsharp mask and CMYK conversion for the press characteristics for each application of an image. Newsprint doesn't offer much brightness to whites, so you can compensate with image adjustements to help keep the image from going even more flat. But doing any of this requires familiarity with the output device characteristics.
If you do this kind of correction, do it to a copy of your master image file rather than to the file itself. For most graphic design output, the compensation for press and paper characteristics is handled in prepress with profiled film or plate output rather than by messing around with each image in Photoshop beforehand.
Since the subject matter of my first image offers some room for interpretation about what effects look natural or not, here's a very basic example of a low contrast sky with puffy clouds. Image 1 matches the slide, Image 2 shows the image with auto levels applied, Image 3 shows the image with auto contrast applied. I don't think auto contrast has does anything very smart. It just maintains the relative balance between the color channel curves while adjusting the levels of the combined channels to meet the black and white points on the histogram.
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The image sequence below shows the correct original low contrast, pale color original image.
It is followed by the same image with auto levels applied. This really pumps up the contrast and alters the color balance to be much warmer, ruining the mood of the image.
The third image shows auto contrast, which retains the relative cool blue color cast, but it still messes up the image with the higher contrast and oversaturation of the color.
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