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DOCS clarify $force_resample behaviour

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Fixes https://github.com/silverstripe/silverstripe-assets/issues/21
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Jonathon Menz 2017-06-28 14:40:18 -07:00
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docs/en/02_Developer_Guides/14_Files/02_Images.md
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@ -141,7 +141,40 @@ For usage on a website form, see [api:FileField].
### Image Quality ### Image Quality
To adjust the quality of the generated images when they are resized add the #### Source images
Whenever SilverStripe performs a manipulation on an image, it saves the output
as a new image file, and applies compression during the process. If the source
image already had lossy compression applied, this leads to the image being
compressed twice over which can produce a poor result. To ensure the best
quality output images, it's recommended to upload high quality source images
(minimal or no compression) in to your asset store, and let SilverStripe take
care of applying compression.
Very high resolution images may cause GD to crash (especially on shared hosting
environments where resources are limited) so a good size for website images is
around 2000px on the longest edge.
#### Forced resampling
Since the 'master' images in your asset store may have a large file size, by
default SilverStripe will always apply compression to your images to save
bandwidth - even if no other manipulation (such as a crop or resize) is taking
place. If you expect the images in your asset store to already have
compression applied and want to serve up the original when no resampling is
necessary, you can add this to your mysite/config/config.yml file:
:::yml
# Configure resampling for File dataobject
File:
force_resample: false
# DBFile can be configured independently
SilverStripe\Filesystem\Storage\DBFile:
force_resample: false
#### Resampled image quality
To adjust the quality of the generated images when they are resampled, add the
following to your mysite/config/config.yml file: following to your mysite/config/config.yml file:
:::yml :::yml
@ -150,24 +183,6 @@ following to your mysite/config/config.yml file:
properties: properties:
Quality: 90 Quality: 90
By default SilverStripe image functions will not resample an image if no
cropping or resizing is taking place. You can tell SilverStripe to always to
always produce resampled output by adding this to your
mysite/config/config.yml file:
:::yml
# Configure resampling for File dataobject
File:
force_resample: true
# DBFile can be configured independently
SilverStripe\Filesystem\Storage\DBFile:
force_resample: true
If you are intending to resample images with SilverStripe it is good practice
to upload high quality (minimal compression) images as these will produce
better results when resampled. Very high resolution images may cause GD to
crash so a good size for website images is around 2000px on the longest edge.
## Changing the manipulation driver to Imagick ## Changing the manipulation driver to Imagick
If you want to change the image manipulation driver to use Imagick instead of GD, you'll need to change your config so If you want to change the image manipulation driver to use Imagick instead of GD, you'll need to change your config so