CONTRAST IS IMAGEDEPENDANT !!!!!

EC
Posted By
Erik_Clemens
Feb 15, 2005
Views
355
Replies
8
Status
Closed
Hi,

I’m using Photoshop CS a lot in combination with AfterFX PRO 6.5. When changing contrast in AfterFX it is completely different from that in PS CS. In afterFX it is completely independent of the image. Just take one completely white image and another image with a white background and some black stripes. Now set Brightness/contrast for both images to -50/-50. In AfterFX the RGB value of the white background will be the same for both images. In PS CS, depending on the percentage of black stripes, this RGB value is completely different. What has happened to the "contrast" slider in PS CS ??? VERY ANNOYING ???
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PC
Pierre_Courtejoie
Feb 15, 2005
Are you sure that it is the case at all zoom ratios?
EC
Erik_Clemens
Feb 15, 2005
Pierre,

Of course I’m talking about the 1:1 ratio, and the exported documents and how I receive them in other applications. Using the same BC values on both images give different white values as output.
PC
Pierre_Courtejoie
Feb 15, 2005
Sorry, I just wanted to scratch out possible resampling errors…
CC
Chris_Cox
Feb 15, 2005
Brightness/Contrast doesn’t care anything about the image contents.

Of course, you probably shouldn’t be using such a crude adjustment in the first place….
EC
Erik_Clemens
Feb 16, 2005
Hi Chris,

As I mentioned in my first post (and I did this in PS CS AND PS Elements 1, which I had somewhere), contrast IS related to the image content; just try it with the images as described. The MAIN issue here is that the "contrast"-behaviour is not consistent between AFX and PS !!! When doing PS work that eventually goes to AFX, it are mostly compostions that have many layered FX. If BC is not consistent I can not use these compositions in AFX !!!

About using crude adjustments: I don’t hope you think that I’m photoshopping on 100% white images all day 😉
EC
Erik_Clemens
Feb 16, 2005
Chris, Hi again,

I thought, since I’m a newcomer with CS, this issue was known somewhere. So either I’m doing something very wrong (Í’m using XPsp1, and tried every imagemode), or nobody cares what this tool is doing, so it never was discovered.

Please try the images as mentioned above and tell me that the white background has the SAME RGB-values in both images after you aplied B/C=-50/-50…
CC
Chris_Cox
Feb 16, 2005
OK, I found in the code where it does calculate the mean value as a pivot point. It’s been that way since at least Photoshop 4 (probably before).

I was mistaken.

And it means that AfterEffects is using different math for some reason.

But, of course, you still shouldn’t be using Brightness/Contrast on any images you care about (it’s a very clumsy adjustment).
DM
dave_milbut
Feb 16, 2005
But, of course, you still shouldn’t be using Brightness/Contrast on any images you care about

don’t tell me! use curves.

oy vay! 🙂

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