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  • #263579
    Profile photo of PA123PA123
    Member

    Hi,

    Hope can get some help for this image processing. This image is taken under strong backlight and is cover by my hand.

    #1 show the image w/o any procees
    #2 show the image after process by me by :
    Change to lab colour, and use curves a and b channel and change back to rgb. (something I learnt in lynda.com)
    Adjust using levels
    Adjust the saturation
    Add abit of blue colour balance

    After the the process, the image shows strong blue color :sad wave: .

    Thanks
    IMG_3202(org).jpg
    IMG_3202-1(800.jpg

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    #296250
    Profile photo of hanYeo, Wee Han
    Spectator

    Peter,

    Looks ok to me. The blue on the legs were alr there in the first pic. Adding saturation and increasing contrast will make them more prominent.

    Hope the PS experts can come in and advise.

    Cheers

    Han

    #296252
    Profile photo of ptleeptlee
    Participant

    Hi Peter,

    I agree with what Han said, the original image looks to have that blue tint in already. Something of a auto WB issue of the camera.

    Anyway, I took your first image and also did the adjustments in LAB to improve contrast. Also removed the dust spots, noise and some sharpening (luminance channel in LAB). What I did extra was in the hue & saturation, I selected and adjusted the blues and magenta. As I can see the blues on the black (ant?) and a tinge of magenta on the spider.

    I reckon this may be closer to what you wanted in terms of colour?

    Cheers,
    PTLee

    PS: BTW, I’m no PS expert :P
    IMG_3202(org).jpg

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    #296253
    Profile photo of ptleeptlee
    Participant

    One more thing I’d like to add, is that LAB is a different way of representation for an image, with A channel representing Green & Magenta, B representing Yellow and Blue. My correction in the hue & saturation tool isn’t exactly the right way of colour correction in LAB mode. :oops:

    LAB is very interesting, but I’ve never quite grasp the idea of doing everything in LAB mode. :?

    Cheers,
    PTLee

    #296254
    Profile photo of wltpchwltpch
    Member

    Hi
    Huh What is LAB?
    Thanks.

    Cheers,
    Loong Tat

    #296303

    Peter,

    I agree with Han and PT and I think PT did a great job in the post processing. BTW, I thought my sensor was dirty, I think you need to scrub your sensor. :twisted:

    Loong Tat,

    You skip class, that why you missed LAB. :D :D

    In Photoshop, the LAB stands for Channel Lightness, A and B (3 color channels). The first channel – Lightness or Luminance, can range from 0 to 100. A Lightness value of 0 equals black and a value of 100 equals white. The higher the value, the more vivid the color. The other 2 channels are Channel A and Channel B, represent color ranges. The A channel has colors ranging from green to red and the B channel contains colors ranging from blue to yellow.

    Cheers,
    SC

    #296307
    Profile photo of wltpchwltpch
    Member

    Hi SC
    Thanks for the explanation. Guess i must have left at the most crucial time :cry:
    The next natural question of course where do u find this LAB function in CS4?
    Thanks.

    Cheers,
    Loong TAt

    #296313

    Loong Tat,

    here is how you convert to LAB Mode:

    Image>Mode>Lab Color (to convert to LAB mode)

    Phek Thong’s notes has the process of how to make use of the LAB mode, take a look at the slide.

    Cheers,
    SC

    #296319

    Sorry, I thought Phek Thong notes has LAB included, I just check it was just a demo in the class. I will put something up when time permit.

    Cheers,
    SC

    #296326
    Profile photo of wltpchwltpch
    Member

    Hi SC
    Thanks alot.
    What is the advantage of LAB mode vs RGB colour mode?

    Cheers,
    Loong Tat

    #296331
    Profile photo of ptleeptlee
    Participant

    LAB is just another way of representing an image. Normally, we’ll get it in RGB representation, sometimes, professional printing would require CMYK (Cyan-Magenta-Yellow & Black). LAB, as SC and myself have mentioned, is a transformation to represent in 3 channels L (lightness/luminance), A channel & B channel.

    One key advantage I find is the ability to sharpen the picture’s L-channel with little worry of the colour ‘bleeding’ and creating a halo around edges.

    The other is the simple process in which to improve the contrast and colour saturation of a more washed out image.

    Typically I would recommend using LAB for landscapes with those ‘hazy’ flat look.

    Refer to this before and after example
    Before
    http://npss.org.sg/forum/viewtopic.php?f=11&t=2225
    after
    http://npss.org.sg/forum/viewtopic.php?f=11&t=2225&start=20

    I don’t normally use LAB on other genres of photography, but apparently it works as well.

    Cheers,
    PTLee

    #296335
    Profile photo of wltpchwltpch
    Member

    Hi PT
    Thanks. All somewhat mysterious to me :)

    Cheers,
    Loong Tat

    #296336
    Profile photo of ptleeptlee
    Participant

    Hi LT,

    It’s ok. I tried reading about it in-depth. The book is still on my shelf collecting dust. :oops:

    Anyway, I’ll post the steps up soon.

    Cheers,
    PTLee

    #296945
    Profile photo of PA123PA123
    Member

    Hi All,

    Thanks for sharing the experience.

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