GIMP can understand a number of different colour formats with a varying degree of support. It supports three so called modes: RGB, grayscale, and indexed.
To change the mode of the image, choose in the menu from <Image> Image > Mode >
Colour Modes[edit | edit source]
GIMP supports the following color modes:
- True Colour (RGB): This has the best support in GIMP. It is made up from 3 channels of tonal variants, making a total of million colours - * *
Supported formats: XCF, PNG, TGA, TIFF, SGI, BMP.
- Grayscale: The grayscale mode uses one channel to display a gray image. GIMP supports grayscale well and is usable for most tools that don't specifically require colour information.
Supported formats: XCF, PNG, TGA, TIFF, SGI.
- Indexed: In this mode, the image consist of pixels picked from a palette of up to colours.
When you convert an image into this mode, or when you are reducing the color depth of an image, dithering options give you control over how colours are scattered. For the best quality results (especially with pictures that have gradual tonal variance) use Floyd-Steinberg dithering: it will give a grainy texture to the picture, but reduce visible banding between different colours. On the other hand, reduced or no dithering will result in smaller files when saved as GIF or PNG (or BMP with the Run-Length Encoded option set).
Supported formats: XCF, PNG, GIF, BMP.
- Monochrome: Two colours, often black and white. GIMP sees this as an indexed image with only 2 colours.
Supported formats: XCF, PNG, GIF, BMP.
Menu items for color modes:
- Image > Mode > RGB
- Image > Mode > Grayscale
- Image > Mode > Indexed
Alpha Channel[edit | edit source]
Regardless of the mode, images can have an optional alpha channel for transparency. An image with an alpha channel can have transparent and semitransparent pixels, the degree of transparency of each pixel ranging from 0 to Using transparency enabled by alpha channel, you can create a picture by stacking several layers on top of each other, save images for the web, or create images for 3D graphics that have holes or semi-opaque areas.
Formats that fully support alpha channel: XCF, PNG, TIFF, TGA, SGI. Formats that only support alpha channel as fully opaque or fully transparent: GIF, XPM.
Only Internet Explorer versions later than version 7 support transparency. Internet Explorer 6 and earlier do not.
Menu items for alpha channel:
- Layer > Transparency > Add Alpha Channel
- Layer > Transparency > Remove Alpha Channel
- Layer > Transparency > Add to Selection
Colour Filter/Tools[edit | edit source]
Image, Mode, Decompose will split a colour image into a set of greyscale images, based on various colour models. Image, Mode, Compose does the opposite, combining greyscale images into colour ones. Striking effects may be obtained by recombining channels in a different model or order than they were decomposed in.
A number of colour adjustments can be found under Image, Colours, and colour effects under Image, Filters, Colours
Bibliography[edit | edit source]
← Editing ·GIMP· Saving →
As with anything else, images come in different kinds and serve different purposes. Sometimes, a small size is important (for web sites) and at other times, retaining a high color depth in all its glory (a family portrait) is what you want. can handle all of this, and more, primarily by converting between three fundamental modes, as seen in this menu. In order to switch your image to one of these modes, you open it and follow that menu and click the mode you want.
Figure Dialog for changing the mode
RGB - This is the default mode, used for high quality rich color images. This is also the mode for most of your image work including scaling, cropping, and even flipping, as it gives the computer more information to work with. The extra information also makes RGB Mode the largest to store as a result.
A little bit of detail if you are interested. Each pixel or point when in this mode consists of three different components. R->Red, G->Green, B->Blue. Each of these in turn can have an intensity value of So, at every pixel, what you see is an additive combination of these three components. All these combinations result in a way to represent millions of colors.
Indexed - This is the mode usually used when file size is of concern, or when you are working with images with few colors. It involves using a fixed number of colors, or less, at each point to represent the color at that point. The defaults to attempting to figure out an "optimum palette" to best represent your image. Try it, you can undo it if you don't like the results, or use a custom palette or more colors.
Figure Dialog “Change to Indexed Colors”
As you might expect, since the information needed to represent the color at each pixel is less, the file size is smaller. However, sometimes, there are options in the various menus that are "greyed" out for no apparent reason. This usually means that the filter or option cannot be applied when your image is in its current mode. Changing the mode to RGB, as outlined above, should solve this issue. If RGB mode doesn't work either, perhaps the option you're trying requires your layer to have the ability to be transparent. This can be done just as easily via → → .
Figure Add Alpha Channel
Grayscale - In case you want to convert your brilliant color image to something that's black and white (with a lot of shades of grey), this is one of the easiest ways in which to do it. Some photos do look a lot fancier when displayed in grayscale. Again, if you're interested in some detail, this is achieved by taking the RGB values at the pixels in your image, and suitably weighted averaging them to get an intensity at that point.
There is no need to convert an image to a specific mode before saving it in your favourite format, as is smart enough to properly export the image.
Hi Rich thanks so much for your response! It's the windows version.
Okay that's good to know. I'll try that plugin thanks so much. Yes it's going to the printers as a PDF, and there are pages all as layers.
Sadly I found out about Scribus too late, and I don't have time to make it all again. Do you know of a way of importing xcf file into Scribus? I've found talk of it on the internet but can't seem to put it into action.
AFAIK No real easy way to go from many layers in Gimp to many pages in Scribus. Scribus is frame based - text frames - image frames, so every page needs to be copied and pasted bit-by-bit Gimp-to-Scribus and formatted as well.
Scribus keeps text as text, embeds the text font information in the PDF and is the way to go.
The problem with Gimp PDF is that embed text part is broken. Make a PDF with Gimp and it looks great on your computer with all your installed fonts. The PDF gets to the printers, they do not have the font(s) installed. Your PDF looks terrible with default replacement fonts.
Not the way to go but you can
1. Export your document as a multipage tif file 2. Use ImageMagick www.imagemagick.org - a command line application to create the CMYK PDF.
What are the snags ? Text is no longer text, it is flattened into graphic (raster) format. Each page is a 'picture' This was the default for Gimp , nothing new.
the command is
magick -colorspace cmyk -profile .pdf
You need that .icc file so a basic generic CMYK.icc attached
..and a 4 minute example video to go with all this. https://youtu.be/35rKA8Bs71E
best of luck
Converting Color Images to B&W
Text and images Copyright (C) Eric R. Jeschke and may not be used without permission of the author.
In this tutorial Ill show you some different ways to convert color RGB images to B&W:
Well examine each of these in turn.
Here is an example image, loaded into GIMP. I thought it might look nice as a black and white image.
Here is what I get if I use the standard mode change to grayscale from RGB.
Duplicate the original image () and right-click on the copy. Select . I dont know how this conversion works in GIMP, but I have read that Photoshop uses a standard mix of the RGB channels for their grayscale conversion: RED=30%, GREEN=59% and BLUE=11%. Supposedly this mix accounts for the eyes sensitivity to different colors. This formula does a pretty nice job in the general case, but some images do not work as well with it, particularly if the green channel component is not strong.
I suspect GIMP uses a similar formula. My experiments with the Channel Mixer (more on this below) support this.
Here is what I get if I use desaturate instead. Duplicate the original image () and right-click on the copy. Select . Unlike the grayscale mode change above, the channels are not remixed in different percentages, so we should expect different results.
The result is visually different; note the increased contrast in the scales. Also, compare the % zoom views at right and in the previous grayscale example. You can see a lot more noise in the desaturated zoomed view (examine the blurred area below the spikes). The reason is that we are getting more blue and red channel noise, whereas in the grayscale mode change operation the algorithm is giving us a remix of 60% of the clean, detailed green channel.
Via Decompose RGB¶
A third method is to consider the red/green/blue channels of the image. Each one can be represented as an independent grayscale image. Right-click on the original image and select . Select the RGB option and click OK.
Here you can see the three channels: red (top), green (middle) and blue (bottom). You can see that the red channel contains most of the luminance information as well as a lot of noise, the green channel has the least noise, and the blue channel has shadows and noise. Often the blue channel has the most noise, but not in this case.
Very often the green channel contains an excellent B&W version of the image. If nothing else, taking a look at the RGB decomposition is important to give you an idea of where the important information is in your image, and where the noise is.
Via Decompose HSV¶
Another possibility is to decompose to Hue/Saturation/Value components and consider the Value image (the other two are not usually useful for this purpose). Right-click on the original image and select . Select the HSV option and click OK.
Via Decompose LAB¶
Yet another decompose option: LAB mode. Right-click on the original image and select Image/Mode/Decompose. Select the LAB option and click OK.
The Lightness component is a very interesting one because it contains all of the luninance information (whereas in RGB and HSV some of that information is spread into other components). You can very often see an expanded tonal range and discover hidden detail in the shadows by examining this component.
Not often useful by itself, but it can be combined with other layers for interesting results (see Tips at end of article).
Note: the LAB decompose option was not distributed with the version of GIMP I got (ver ). I dont know whether it comes bundled with newer versions. I downloaded it from the GIMP Plug-in Registry and compiled it myself.
Via Decompose CMYK¶
Just for fun I tried decomposing into CMYK. The Black channel is interesting: it resembles a negative.
Via Channel Mixer¶
The final technique is the Channel Mixer filter. Right-click on the original image and select .
Youll get a dialog box like the one at right. Click the checkbox that says Monochrome. Make sure the preview checkbox is also checked.
Now play around with the levels of the three channels, seeing the results in the preview window. If you dont want to change the overall brightness of the image then the three values should add up to %, but feel free to experiment (checking the Preserve Luminosity box will also preserve the overall brightness of the imagesee the Tips section below for more explanation of this option). Dialing in Red=30%, Green=59%, Blue=11% ought to give you something that looks nearly identical to what you would get with a mode change to grayscale.
When you have something that looks decent in the preview, click OK. If you dont like the look of the result, Undo () and reapply the filter with different settings ().
The advantage of the channel mixer is (obviously) flexibility. I like to decompose and examine the individual RGB channels, as we did earlier. That way I can see what is good and bad about each, and then use the channel mixer to combine them accordingly. In this example, I could see that the green channel did not really have much to offer, and had the least contrast in the iguanas scales; still, I mixed in 30% to help with the noise. I liked the blue channel for the great contrast it adds to the scales. Reds got a lot of noise, but I mixed in just enough to use some of the contrast and luminance information. You can see from the close up that it isnt quite as good the grayscale version in terms of noise, but the noise isnt too bad, and the trade-off is a lot more contrast and interest in the overall tonalities of the image.
Note: the channel mixer plug-in was not distributed with the version of GIMP I got (ver ). I dont know whether it comes bundled with newer versions. I downloaded it from the GIMP Plug-in Registry and compiled it myself.
- Once you have a good B&W version of your image you may be interested in adding some simulated film grain.
If you are wondering what the Preserve Luminosity option does in the Channel Mixer, I have the answer. I was curious myself, and asked the author of the Channel Mixer, Martin Guldahl, about it. This was his reply:
The Preserve Luminosity option just maintains the luminosity at the same level regardless of the slider values.
For example, suppose the sliders were are Red%, Green%, Blue:0%. With Monochrome on and the Preserve Luminosity option off, the resulting picture would be at 75%+75%+0% =%, very bright indeed. A pixel with a value of, say, R,G,B=,,80 would map to ++80*8= for each channel. With the Preserve Luminosity option on, the sliders will be scaled so they always add up to %. In this example, that scale value is 1/(75%+75%+0%) or So the pixel values would be about The Preserve Luminosity option just assures that the scale values from the sliders always adds up to %. Of course, strange things happen when any of the sliders have large negative values.
Left image: The original image. Right image: Converted using channel mixer (80% green, 20% red).
Left image: The original image. Right image: Converted using channel mixer.
The original tutorial used to appear on gimpguru.
Convert to rgb gimp
I recently wanted business cards printed. I knew there was a difference between RGB codes -colors that are generally used for the web or that show up on you monitor, and CMYK codes, -colors used by professional printers. Since GIMP uses RGB colors by default I found out how to add a GIMP CMYK plugin to convert RGB to CYMK color codes and vice versa. Plus, this method works in reverse to convert Photoshop CMYK psd files to RGB in GIMP.
For those that dont know about the differences between RGB and CYMK, heres my simple explanation. Basically a color in RGB is represented by a hex code or a combination the primary colors of light -combos of red, blue and green as seen on your monitor. As a result, RGB colors tend to be bright and vivid. CMYK is based on colors of pigment used when printing. Specifically CMYK uses cyan, magenta, yellow, and black to create printed colors. Due to the addition of black, CMYK colors dont have same vibrance as their RGB equivalence. If you convert a RGB color to CMYK it will appear darker due to the incorporation of black as the 4th color in printing. Should you desire the exact same look in print from your monitor, youll have to make color adjustments. But if you plan on creating designs for print its best to convert to CYMK color. That means adding capability to GIMP for CYMK.
First, I Googled to see if there was a GIMP CMYK plugin. The separate plugin, last update , was available but most of what I found on this plugin was focused on older GIMP x versions. I have the latest GIMP version of and determined that I needed newer CYMK capability. I found the Cyan app from GitHub -my thanks to the author of this software. It works with my version of GIMP, and it would also use Adobe ICC CYMK profiles in GIMP. So I needed 2 things to make GIMP understand CMYK: 1) the Adobe ICC profiles and 2) the Cyan app integrated with GIMP.
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The Cyan program actually installs separately from GIMP but appears to show up in the GIMP menu and allows import/export of files. I think this actually makes it easier to install and use. So installing Cyan is like any typical dmg app for mac. As mentioned it uses ICC color profiles used by CYMK. I checked on my mac and there are a couple of default ones, but I went ahead to Adobes site here and downloaded their ICC profiles. I then copied and pasted the unzipped files into the ColorSync Profile folder so both Cyan and GIMP would see the ICC files. However, the addition of these extra ICC profiles is optional as far as I can tell.
Here is the process I used to allow GIMP to convert from RGB to CYMK or from CYMK to RGB. There arent a lot of options with this although I dont think options are needed.
First, get the Adobe ICC profiles. They can be download from here.
Adobes instructions are very straightforward. To install the Adobe ICC profiles on Mac OS X:
Install profiles in one of two locations.
Copy all of the ICC profiles to the \Users\Library\ColorSync\Profiles folder. Profiles installed in this location will be available only to the user who installed the profiles. or Copy all of the ICC profile files included in this archive to the \Library\ColorSync\Profiles folder. Installing in this location requires the user to be an administrator of the system. Profiles installed in this location will be available to all users.
I downloaded and unzipped the files. I used the Go To Folder menu to locate the default ICC profiles. Mine were located at \Users\MyHomeDir\Library\ColorSync\Profiles where MyHomeDir was the name of my home directory; yours will be named differently. In this case my files were located at \Users\martha\Library\ColorSync\Profiles. Simply highlight the Adobe files, copy and paste or drag into the profiles folder. I would guess on windows that searching in Explorer for ICC files would show a similar location where the Adobe ICC profile files could be placed.
The next step is to download the Cmyk plugin. It can be found here and is operating system specific. Ive download the Mac version. Click to install the dmg file and then drag it into the Applications folder on Mac. Again, since Im not doing this on Windows Im guessing that running the executable will install the program.
Next I opened the Cyan program outside of GIMP to set some of the defaults listed at the bottom of the Cyan window.
Now that the ICC files and plugin are installed lets see how to use the CMYK plugin for GIMP to convert to and from RGB.
Converting from RGB colors to CYMK in GIMP
For printing purposes before converting, always check to make sure that the image you are saving is in DPI. If it is not at this high resolution then use GIMP to set it to that before exporting for print. You can do this with the following step.
Once you have confirmed and/or set the DPI to you can proceed to convert GIMPs default RGB to CYMK.
Open GIMP, click File Open and select the image. Now click the Cyan in the GIMP menu at the top.
Click Cyan > Export File. This opens the Cyan app. See that the input at the top says GIMP sRGB while the output says none. Ill change that through the dropdown to an Adobe ICC profile for CYMK.
Once Ive done that, the image information to the right of the image will change (I wont bother with a new image since it looks the same except for that).
Using the Cyan File > Save menu will save the file as a TIF format that retains the cymk settings for print. On mac, you can right click the image and use Show info to confirm that the image resolution is DPI, the color is CMYK, and the CMYK color profile you selected.
Converting from CMYK to RGB in GIMP
This is very similar to the above except in reverse steps so I wont go into much detail. This is the process to convert Adobe CMYK psd or ai files to sRGB files in GIMP.
Open GIMP and select File New to show a blank workspace. Then choose Cyan > Import File from the GIMP menu. It will open Cyan.
Once in Cyan, click File Open and select the CMYK file. Now it will show the input as CYMK colors and the output as none.
While still in Cyan, click on File > Save to place a copy into the GIMP workspace where you can edit in GIMP as you would normally do. Note: If you save or export this image without changing this the CYAN output will default to GIMPs sRGB color profile for use in GIMP.
And thats how you add CYMK capability to the latest version of GIMP. You can use it to convert RGB to CMYK for high resolution printing or to convert Adobe CMYK files to RGB so you can edit them with GIMP
If you found this useful, please consider sharing it.
How to Convert an Image to RGB Color Mode
* This option has the ability to apply multiple colors to an image.
* The colors Red, Greenand Blueare added to an image when this tool is used.
Steps to Follow:
- Start GIMP.
- Launch a new image file.
- Select the entire image by just by clicking Select -> All or press Ctrl+A.
- Click Colors -> Maximum RGB.
- A box with a name Maximum RGB Valuegets displayed.
- Initially click the "Preview" check box to view the image simultaneously while applying the changes.
- Now, choose either "Hold the maximal channels" or "Hold the minimal channels" option to have bright or dim effect on the image and finally click the Ok button.
- The changes applied to the picture gives a different look to the image.
- Now the image is changed to RGB color mode.
- Finally save the file by clicking the "File->Save" button.
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As with anything else, images come in different kinds and serve different purposes. Sometimes, a small size is important (for web sites) and at other times, retaining a high color depth (e.g., a family portrait) is what you want. can handle all of this, and more, primarily by converting between three fundamental modes, as seen in this menu. In order to switch your image to one of these modes, you open it and follow that menu and click the mode you want.
Figure Dialog for changing the mode
RGB- This is the default mode, used for high-quality images, and able to display millions of colors. This is also the mode for most of your image work including scaling, cropping, and even flipping. In RGB mode, each pixel consists of three different components: R->Red, G->Green, B->Blue. Each of these in turn can have an intensity value of What you see at every pixel is an additive combination of these three components.
Indexed- This is the mode usually used when file size is of concern, or when you are working with images with few colors. It involves using a fixed number of colors ( or less) for the entire image to represent colors. By default, when you change an image to a palleted image, generates an “optimum palette” to best represent your image.
Figure Dialog “Convert Image to Indexed Colors”
As you might expect, since the information needed to represent the color at each pixel is less, the file size is smaller. However, sometimes, there are options in the various menus that are grayed-out for no apparent reason. This usually means that the filter or option cannot be applied when your image is in its current mode. Changing the mode to RGB, as outlined above, should solve this issue. If RGB mode doesn't work either, perhaps the option you're trying requires your layer to have the ability to be transparent. This can be done just as easily via → → .
Figure Add Alpha Channel
Grayscale- Grayscale images have only shades of gray. This mode has some specific uses and takes less space on the hard drive in some formats, but is not recommended for general use as reading it is not supported by many applications.
There is no need to convert an image to a specific mode before saving it in your favorite format, as is smart enough to properly export the image.