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Learn To Adjust Contrast Like a Pro in Photoshop, GIMP, and Paint.NET

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Brightness and Contrast tools are for beginners! Ever wondered what graphics programs offer advanced users to ensure their photographs have a great value range? Read on to learn about Levels, Curves, and Histograms in three major programs.

Curves and Levels are not as intuitive as the more basic Brightness and Contrast sliders Photoshop, GIMP, and Paint.NET all share. However, they offer a great deal more control over images that professionals and skilled image editors will demand. Combine these tools with a knowledge of how basic histograms work, and you’ll be well on your way to editing contrast like a pro!

What is a Histogram?

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Histograms are confusing looking collections of information, and are not obviously understood unless they are explained. The left is the histogram tool in Photoshop (Window > Histogram), the right is the Histogram tool in the GIMP (Colors > Info >Histogram). Out of the box, Paint.NET does not have a stand alone Histogram tool, but has them built into other tools that we will discuss later.

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You can think of a histogram as a sort of simple algebraic mapping of the information in your image. Your horizontal (x axis) represents your value range, from your darkest blacks on your left side, to your lightest whites on your right. Your vertical (y axis) shows the concentration of that value in your image. The higher the peaks, the more of that color is in your image. High peaks on the right side represents high amounts of light values, highlights and whites, while high peaks on the left represents a high concentration of dark, black, low light values.

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Histograms can be made for any color channel, or for combinations of those channels, although you might see quite different information depending on which you are looking at. Remember that all photographs are made of image channels, all of which have their own range of values, but can also be combined to create a complete image. Regardless of all that, you can learn a lot of useful information checking out how the values are distributed in your images.

Brightness and Contrast Tools

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Brightness and contrast, as we discussed, are easy to understand methods for editing photographs. They give you only basic edits to your value range, clunkily bloating, stretching, and distorting your value range, giving less than perfect control over the parts of your histogram you want to change. Pictured above are the Brightness and Contrast tools for Paint.NET (left) and the GIMP (right).

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Ideally, a good, balanced image should have good detail in the lights and darks, as well as a good value range throughout, without a lot of dynamic high peaks in any area. Brightness and contrast tools simply “stretch” the entire range out to create brighter images, leaving gaps in the histogram without bringing out details in either the highlights or darks.

Working with Levels

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Levels are the superior tool for adjusting histograms, and bringing out rich value ranges in an image. GIMP’s Levels tool (left) and Photoshop’s (right) look very similar. They have two basic sliders, one for Input Levels, and another for Output Levels.

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Input levels allow you to adjust your range of values by adjusting three points within the horizontal axis. Moving the “Darks” point will make all of your darks heavier and blacker. Adjusting your “Lights” point will make all of your highlights brighter and lighter. And adjusting the middle point will cause your value range to lean one way or another, either lighter or darker, effectively compressing that part of the old histogram, while stretching out detail in other parts.

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Output Levels give you direct control of the Y-Axis of your histogram, and allow you to set a ceiling for how dark your darks can be, and how light your lights can be. Used in combination with adjustments to Input Levels, detail can be coaxed out of even stubborn images.

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It is worth noting that Paint.NET’s Levels tool is slightly different than either Photoshop or GIMP. It is no more complicated than either, and a basic understanding of histograms and some patience will allow you to make any adjustment you could make in Photoshop or GIMP.

How to Use Curves

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Curves are yet another way to look at adjusting the same color information, with the exception that it is a considerably more complex tool, allowing for fine tuning and microadjustments to images.

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On the basic curve, the vertical axis represents the Output Levels, which sort of turns your histogram on its head. In its natural state, the “curves” line represents a 1:1 ratio, or a straight rise/run diagonal line. This means that the darkest parts of the horizontally noted values should have an equal, corresponding value in your vertical axis. What does all this mean? Basically, you have the ability to subtly put a ceiling on your lights and darks, while creating potentially complex adjustments to the other parts of your image.

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Drastically different images can be created by distorting curves. Midtones can be made into highlights, darks into lights, highlights into midtones, and all with the same basic set of tools.

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For even further complication, curves can be adjusted per channel, like Levels. This allows for an impressive level of customization, allowing graphics power users to coax better, richer information by editing channels independently and together. This can allow you to, perhaps, shift your highlights to be more yellow or gray, while making your shadows more red or blue. Curves can prove a vital set of tools for any photographer, from amateur to seasoned pro.


While the program’s visuals may differ slightly from Photoshop to GIMP to Paint.NET, you can expect the power of these tools to remain the same. Expect some minor differences in the user interface, with the core functionality intact.

Image Credit: All images by Guillaume Boppe, available under Creative Commons.

Eric Z Goodnight is an Illustrator and Graphics Geek who hopes to make Photoshop more accessible to How-To Geek readers. When he’s not headbanging to heavy metal or geeking out over manga, he’s often off screen printing T-Shirts.

  • Published 03/2/11

Comments (23)

  1. dragonbite

    Great overview! I like how everything was described and included a couple image editing programs, rather than just one “industry standard” one which many people don’t necessarily have.

  2. jimkiler

    typo?

    In the fourth paragraph you state the following:

    “High peaks on the left side represents high amounts of light values, highlights and whites, while high peaks on the right represents a high concentration of dark, black, low light values.”

    shouldn’t it be reversed so you say light values, highlights and whites are on the right and dark, black, low light values are on the left.

  3. Eric Z Goodnight

    @jimkiler: Wow, thanks for that catch. Fixed.

  4. homeie

    I LIKE IT!!!!!!!!!

  5. R77R

    Great article! :D The missing point is print-friendly button.
    When will HTG implement print button?

  6. fgr

    Great article!
    But… when I print this article, all the text is black on black background! no good. Not sure if it is my settings or this html.

    Yeah A “print-friendly” button would be really nice.

  7. Digirati

    Uhhh….. FGR, look at your options in your browser. It gives the option to print backgrounds or not print them. It’s not the pages fault.

  8. fred

    Great Yes I agree that it is missing a missing point is print-friendly button. but it printed great for and I have saved it thanks ..

  9. Aethec

    You might want to mention the excellent Curves+ Paint.NET plugin by pyrochild: http://forums.getpaint.net/index.php?showtopic=3749
    It has histograms, HSV curves, straight curves (…a.k.a. lines), advanced curves with custom input/output, and more!

  10. Ray_O

    Very good article. Locally we started a photography group of which I am the key person to give the discussions and lessons. The questions about Histograms has arisen more than once and this is the best explaination I have seen about them yet.

    Most of the amateur photographers cannot afford Adobe full blown editor so we use Paint.Net (which has almost 700 additional plugins you can download and GIMP. A few member do have Adobe Elements and also a couple just use Picasa3 which I do not advise usage of because Picasa only stores files in JPG format and the compression will cause loss of detail.

    So, PLEASE write more on the GIMP (poor man’s Photoshop) and Paint.Net as you do same me a lot of work (lol).

    Tumbleweed Photography Group
    Cochise Cty, SE Arizona.

  11. SqueezySue

    I’m an amateur photographer and this article was a big help. It made much more sense than what I’ve read in books, and has made me aware of low-priced software to use. Thanks so much.

  12. Mick

    A very good article, congrats. Well writen with good explinations, but not over-explained like some I have read, I only wish I had come across this when I was trying to get my head around histograms, it would have saved me alot of head scratching, and maybe I wouldn’t have a bold pach now ;-)
    ATB
    Mick

  13. Ray_O

    Very good article. Locally (SE AZ) we started a photography group of which I am the key person to write the discussions and lessons. The questions about Histograms has arisen more than once and this is the best explaination I have seen about them.

    Most of the amateur photographers cannot afford the Adobe Photoshop (full blown editor) so we use Paint.Net (which has almost 700 additional plugins you can download) and GIMP. A few members do have Adobe Elements and also a couple just use Picasa3 which I advise caution in it’s usage because Picasa only stores files in JPG format and the compression will cause loss of detail.

    So, PLEASE write more about GIMP (poor man’s Photoshop) and Paint.Net as you do save me a lot of work (lol).

    Tumbleweed Photography Group
    Cochise Cty, SE Arizona.
    (Correction of earlier post)

  14. criss

    Wow,Very good article Well writen with good explinations some I have read, but not over-explained like

  15. one world

    Hi…thanks for the article and overview. But…sorry….I guess I must just not be as smart as the other users of this blog. But, for me, even though the article gives an idea of what “can” be done…..there’s just not enough information for to know how to actually *DO* it.

    For example:
    “It is worth noting that Paint.NET’s Levels tool is slightly different than either Photoshop or GIMP. It is no more complicated than either, and a basic understanding of histograms and some patience will allow you to make any adjustment you could make in Photoshop or GIMP.”

    Ok…but as paint.net user I’d like to know more than this. I’d like to know how…..

    Also:
    “What does all this mean? Basically, you have the ability to subtly put a ceiling on your lights and darks, while creating potentially complex adjustments to the other parts of your image.” — ok…how??

    So as I said, maybe for others these are stupid questions with obvious answers. Sorry about that….but for me….I’m still a little lost….

  16. Antriksh

    Windows Live Photo Gallery gives you two simple sliders to adjust shadows and highlights. I found it really really effective since I started using the app. Now I actually understood how it works.

    Just wanted to point out: You don’t really need huge and heavy apps to adjust the contrast like a pro.

  17. Ker Ong

    Hi Eric,

    While these programs are amazing, the ideal would be to incorporate some kind of auto-fix button that compares an example of a perfect histogram to the example of the users’ histogram and then adjusts it to the umpteenth degree getting the most out of your photo that is possibly can; while at the same time leaving all those manual adjustments still available to those photo-meisters who think they can do a better job themselves. Up to now there doesn’t seem to be any “magic-button” that can do that.

    Kerong

  18. PickledPicas

    I hope you are editing a ‘copy’ of the original photo, before all this editing.

    Most Photo Editing programs DO have an Auto-fix feature. Most Auto-fix settings, need help. That’s why you have manual buttons… to ‘fix’ or ‘mess it up’ yourself.

    Have you ever noticed some of your photos don’t seem to change, when you use Auto-Fix? That’s a good thing. It’s one sign of a good editing program. I take it as a compliment!

  19. Mateng

    I use levels in PS CS1 on almost every photo. One addition to this great list here: if you want to improve only parts of your photo (for example if the center of the photo is hidden in the shadow, or on a face that came out too dark):

    1. Create a selection that covers slightly more then the desired area.
    2. Then feather the selection by a very high amount (I sometimes use 250 px several times on one selection).
    3. Then do one of the tricks that is mentioned above. You see that you can modify a part of the image without changing bits that are just fine.

  20. Guillaume Boppe ;-)

    Hi,
    thanks for using my shots! (I didn’t kew in fact…, but no problem!)
    I will play with them following your advices…
    Best regards
    Guillaume

  21. Eric Z Goodnight

    Guillaume, nice to hear from you. I quite like your shots, and you had so many on Flickr! Not every shot turns out great, as you know, so it was nice to find bracketed shots of good quality I could play with for this tutorial. Keep up the great work!

  22. Richard

    Hey, why don”t you included Paint Shop Pro, when you talk about photo editing?

  23. star

    سلام
    دستت درد نکنه خیلی خوب بود
    ممنون از این اطلاعات خوبی که در اختیارمون گذاشتی

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