GIMP是免费使用的开源光栅图形编辑器，为用户提供了几种制作黑白彩色图像的方法。在本文中，我们将讨论黑白和灰度图像之间的区别。然后我们将介绍几种可以使用 GIMP(use GIMP)将RGB彩色图像转换为灰度模式或黑白模式的方法。
对于本GIMP教程，我们使用了可用于(GIMP)Microsoft Windows的最新版本GIMP 2.10。从gimp.org下载(Download GIMP)适用于Windows、MacOS和Linux的 GIMP 。
黑白与灰度
黑白和灰度有什么区别？在黑白摄影中，这些术语可以互换使用。考虑下图。
这是RGB模式下的彩色照片。如果我们去掉颜色，它看起来像这样：
大多数人会将这张无色图像描述为黑白照片，但更准确的术语是“灰度”。虽然黑色是图像中使用的唯一颜色，但图像由从纯白色到纯黑色的一系列灰色阴影组成。
在照片编辑世界中，区分灰度和真正的黑白是很重要的，它只使用黑白而没有灰度。这是真正的黑白图像。
在GIMP(GIMP)中制作黑白图像的第一步是决定是将其转换为真正的黑白图像还是灰度图像。我们将在下面介绍两者。
如何在GIMP中将(GIMP)彩色(Color)图像转换为真正(White)的(True Black)黑白
GIMP 将彩色图像转换为黑白的过程涉及使用阈值(Threshold)工具。
- 在GIMP(GIMP)中打开您的图像。我们将使用这张两只五颜六色的鸟的图像。
- 在颜色(Colors)菜单中，选择阈值(Threshold)。此工具将当前图层或选区转换为黑白图像。这是我们的图像现在的样子。
- 请注意“应用阈值”(Apply Threshold)对话框中的“通道”(Channel)滑块。左右移动以调整阈值，直到您喜欢所看到的为止。
- 选中拆分(Split)视图框以查看应用于一半图像的阈值，以便您可以将其与原始彩色图像进行比较。
- 当您对阈值感到满意时，单击“确定”。
曾经的全彩色图像现在是纯黑白的，您甚至不需要购买Adobe Photoshop。
如何在GIMP中制作(GIMP)图像灰度(Image Grayscale)
在GIMP(GIMP)中有几种方法可以将彩色图像转换为灰度图像。
将(Convert)图像(Image)转换为灰度模式(Grayscale Mode)
在GIMP(GIMP)中制作灰度图像的最快、最简单的方法是将文档颜色模式转换为灰度。
- 选择图像 > 模式 > 灰度。
4. 您的彩色图像现在将仅由黑色、白色和灰色像素组成。
注意：一旦将图像转换为灰度，就不能再返回彩色。在开始之前保存彩色图像的副本。此外，请注意更改图像的颜色模式适用于整个图像，即使您只选择了图像的一部分。
(Make)使用单声道混合器(Mono Mixer)制作图像灰度(Image Grayscale)
要使用 GIMP 的Mono Mixer工具将彩色图像转换为灰度，请执行以下步骤：
- 选择Colors > Desaturate > Mono Mixer。（或者，右键单击以访问相同的菜单选项。）
- 如果您选中了预览(Preview)框，您将看到彩色图像现在以灰度显示。
- 默认情况下，每个颜色通道将设置为 0.333。尝试更改一个或多个通道的比率。在下面的示例中，我们将红色通道乘数的设置增加到 1.826，将绿色通道乘数增加到 0.930，将蓝色通道乘数增加到 0.686。无论您对通道混音器进行什么更改，
选中Preserve luminosity 框都会将亮度保持在同一水平。(Preserve)
如您所见，在Mono Mixer中调整(Mono Mixer)RGB通道可以产生很大的不同。
去色(Desaturate)以将彩色(Color)图像变为灰度
将彩色图像转换为灰度的第三种方法涉及调整图像的饱和度。
- 选择Colors > Desaturate > Desaturate。
- 使用Mode下拉菜单，尝试各种选项，包括Luminance、Luma、Lightness、Average和Value。选中拆分(Split)视图框以将去饱和图像与原始图像进行比较。
- 当您对结果感到满意时，单击“确定”。
如何在GIMP中使用颜色到(GIMP)灰色工具(Gray Tool)
您还可以使用 Color to Gray工具将图像转换为GIMP中的灰度。
- 选择Colors > Desaturate > Color为灰色(Gray)。
- GIMP没有提供任何关于“颜色转灰色(Gray)”工具究竟做什么的文档，但正如您从下图中看到的那样，效果比简单的去饱和更具艺术性。
- 尝试使用Radius、Samples和Iterations滑块以及Enhance Shadows复选框来实现不同的效果。下图具有以下设置：Radius – 217、Samples – 5和Iterations – 23。
使用色相饱和度工具(Hue-Saturation Tool)在GIMP中制作灰度图像(Grayscale Image)
色相饱和度(Hue-Saturation)工具是另一种在GIMP中制作灰度图像的方法。
- 选择颜色 > 色相饱和度。
- 将饱和度设置(Set Saturation)为 -100 或将滑块一直向左移动以将图像变为灰度。
- 单击确定。
如您所见，在GIMP(GIMP)中有很多方法可以使图像变成黑白图像。通过了解多种方法，您更有可能找到最适合您正在编辑的图像的方法。
做出大胆的选择
许多图像编辑归结为反复试验，因此不要害怕探索所有可用的工具——无论您使用的是GIMP、Photoshop还是其他图像编辑应用程序(image editing app)。
要开始使用，请尝试我们在 GIMP 中创建透明背景(creating a transparent background in GIMP)的教程，您将在其中学习如何使用图层蒙版。或者尝试使用GIMP 插件来(plugins for GIMP)扩展应用程序的功能。
How to Make an Image Black and White in GIMP
GIMP, thе free-to-υse, open source rаster graphics editor gіνеs users several ways to make a color image black and white. In thiѕ article we’ll discuss the difference between black & white and grayscale images. Then we’ll go over a few ways you can use GIMP to convert an RGB color image into grayscale mode or black and white.
For this GIMP tutorial, we used the most recent version available for Microsoft Windows, GIMP 2.10. Download GIMP for Windows, MacOS, and Linux from gimp.org.
Black and White vs. Grayscale
What’s the difference between black and white and grayscale? In black and white photography, the terms are used interchangeably. Consider the image below.
This is a color photo in RGB mode. If we remove the color, it looks like this:
Most people would describe this colorless image as a black and white photo, but a more accurate term is “grayscale.” While black is the only color used in the image, the image is composed of a spectrum of shades of gray spanning from pure white to pure black.
In the photo editing world, it’s important to distinguish between grayscale and true black and white, which uses only black and white and no shades of gray. Here’s the same image in true black and white.
The first step to making an image black and white in GIMP is to decide whether to convert it to a true black and white image or to grayscale. We’ll cover both below.
How to Convert a Color Image to True Black and White in GIMP
GIMP’s process for converting a color image into black and white involves using the Threshold tool.
- Open your image in GIMP. We’ll use this image of two colorful birds.
- In the Colors menu, select Threshold. This tool turns the current layer or selection into a black and white image. Here’s how our image looks now.
- Note the Channel slider in the Apply Threshold dialog. Move it left and right to adjust the threshold until you like what you see.
- Check the Split view box to see the threshold applied to half the image so you can compare it to the original color image.
- When you’re satisfied with the threshold, click OK.
What was once a full-color image is now purely black and white, and you didn’t even need to buy Adobe Photoshop.
How to Make an Image Grayscale in GIMP
There are several ways to turn a color image into grayscale in GIMP.
Convert the Image to Grayscale Mode
The fastest, easiest way to make a grayscale image in GIMP is to turn the document color mode to grayscale.
- Select Image > Mode > Grayscale.
4. Your color image will now be composed solely of black, white, and gray pixels.
Note: Once you convert an image to grayscale, you can’t go back to color. Save a copy of the color image before you begin. Also, be aware that changing an image’s color mode applies to the entire image, even if you’ve only selected part of the image.
Make an Image Grayscale with the Mono Mixer
To use GIMP’s Mono Mixer tool to turn a color image to grayscale, follow these steps:
- Select Colors > Desaturate > Mono Mixer. (Alternatively, right-click to get to the same menu options.)
- If you have the Preview box checked, you’ll see that the color image now appears in grayscale.
- By default, each color channel will be set to 0.333. Experiment with changing the ratios for one or more of the channels. In the example below, we’ve increased the settings for the red channel multiplier to 1.826, the green channel multiplier to 0.930, and the blue channel multiplier to 0.686. Checking the Preserve luminosity box will keep the luminosity at the same level no matter what changes you make to the channel mixer.
As you can see, adjusting the RGB channels in the Mono Mixer can make a big difference.
Desaturate to Turn a Color Image to Grayscale
A third method for converting color images to grayscale involves adjusting the image’s saturation.
- Select Colors > Desaturate > Desaturate.
- Using the Mode drop-down, try the various options including Luminance, Luma, Lightness, Average, and Value. Check the Split view box to compare the desaturated image with the original.
- When you’re satisfied with the results, click OK.
How to Use the Color to Gray Tool in GIMP
You can also use the Color to Gray tool to convert an image into grayscale in GIMP.
- Select Colors > Desaturate > Color to Gray.
- GIMP doesn’t offer any documentation about what exactly the Color to Gray tool does, but as you can see from the image below, the effect is more artistic than simply desaturating.
- Experiment with the Radius, Samples, and Iterations sliders and the Enhance Shadows checkbox to achieve different effects. The image below has the following settings: Radius – 217, Samples – 5, and Iterations – 23.
Use the Hue-Saturation Tool to Make a Grayscale Image in GIMP
The Hue-Saturation tool is yet another way to make a grayscale image in GIMP.
- Select Colors > Hue-Saturation.
- Set Saturation to -100 or move the slider all the way to the left to turn the image into grayscale.
- Click OK.
As you can see, there are many ways to make an image black and white in GIMP. By knowing multiple methods, you’re more likely to find one that works best for the image you’re editing.
Make Bold Choices
A lot of image editing comes down to trial and error, so don’t be afraid to explore all the tools at your disposal—whether you’re using GIMP, Photoshop, or another image editing app.
To get started, try our tutorial on creating a transparent background in GIMP where you’ll learn how to use a layer mask. Or experiment with plugins for GIMP that will extend the app’s functionality.
