| Capítulo 6. Obtener imágenes del GIMP | ||
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Parte II. ¿Cómo convertirse en un mago del GIMP? |  |
| Capítulo 6. Obtener imágenes del GIMP | ||
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Parte II. ¿Cómo convertirse en un mago del GIMP? | |
Tabla de contenidos
One of the most common uses for GIMP, is to prepare images for web sites. This means that images should look as nice as possible while keeping the file size as small as possible. This step-by-step guide demonstrates how to create small files with minimal loss of image quality.
An optimal image for the web depends upon the image type and the file format. Use JPEG for Photographs because they usually have many colors and great detail. An image with fewer colors, such as a button, icon, or screenshot, is better suited to the PNG format.
First, open the image as usual. I have opened our Wilber as an example image.
The image is now in RGB mode, with an additional Alpha channel (RGBA). There is usually no need to have an alpha channel for your web image. You can remove the alpha channel by flattening the image.
A photograph rarely has an alpha channel, so the image will open in RGB mode rather than RGBA mode; and you won't have to remove the alpha channel.
![[Nota]](images/note.png)
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If the image has a soft transition into the transparent areas, you should not remove the alpha channel, since the information used for the transition is not be saved in the file. To save an image with transparent areas that do not have a soft transition, (similar to GIF), remove the alpha channel. |
After you have flattened the image, save the image in the PNG format for your web site.
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You can save your image in the PNG format with the default settings. Always using maximum compression when creating the image. Maximum compression has no affect on image quality or the time required to display the image, but it does take longer to save. A JPEG image, however, loses quality as the compression is increased. If your image is a photograph with lots of colors, you should use jpeg. The main thing is to find the best tradeoff between quality and compression. You can find more information about this topic in ???. |
If you want to reduce the size of your image a bit more, you could convert your image to Indexed mode. That means that all of the colors will be reduced to only 256 values. Do not convert images with smooth color transitions or gradients to indexed mode, because the original smooth gradients are typically converted into a series of bands. Indexed mode is not recommended for photographs because after the conversion, they typically look coarse and grainy.
Figura 6.2. The indexed image
An indexed image can look a bit grainy. The left image is Wilber in its original size, the right image is zoomed in by 300 percent.
Use the command described in Sección 6.3, “Modo” to convert an RGB image to indexed mode.
After you convert an image to indexed mode, you are once again able to save the image in PNG format.
There are two different approaches used by graphic file formats for supporting transparent image areas: simple binary transparency and alpha transparency. Simple binary transparency is supported in the GIF format; one color from the indexed color palette is marked as the transparent color. Alpha transparency is supported in the PNG format; the transparency information is stored in a separate channel, the Alpha channel.
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The GIF format is rarely used because PNG supports all the features of GIF with additional features (e.g., alpha transparency). Nevertheless, GIF is still used for animations. |
Procedimiento 6.1. Creating an Image with Transparent Areas (Alpha Transparency)
First of all, we will use the same image as in the previous tutorials, Wilber the GIMP mascot.
To save an image with alpha transparency, you must have an alpha channel. To check if the image has an alpha channel, go to the channel dialog and verify that an entry for “Alpha” exists, besides Red, Green and Blue. If this is not the case, add a new alpha channel from the layers menu; + → .
The original XCF file contains background layers that you can remove. GIMP comes with standard filters that supports creating gradients; look under +. You are only limited by your imagination. To demonstrate the capabilities of alpha transparency, a soft glow in the background around Wilber is shown.
After you're done with your image, you can save it in PNG format.
Figura 6.4. The Wilber image with transparency
Mid-Tone Checks in the background layer represent the transparent region of the saved image while you are working on it in GIMP.
