The Quality value explained in the last chapter is also used as the threshold value for an optional warning message in high resolution images, i.e. if images need to be massively downsized by the Publisher, as this may bring forth/worsen existing image grain (noise, artifacts, error pixels). This effect also turns up, if the image is extensively cropped by the user inside the Publisher, as this corresponds to a zoom operation.
Such artifacts are wrongly attributed to the Publisher and it’s downsizing/cropping of images, when in fact they usually originate from the camera chip and are already contained in the high resolution image. You can only see this grain by zooming into the original image at 100% in an image editor. Example:
Original image, shot at ISO 400, zoomed to 100% |
|
There are thus two main problems in high resolution pocket cameras (> 10 million pixels):
| • | They produce a lot of noise (error pixels, grain) in higher ISO settings or bad lighting situations, because the camera chip is too small for the amount of pixels crammed onto it. |
| • | They try to remove this noise through an internal camera softening algorithm, thus destroying color saturation and texture. |
To warn the user about this effect, you can turn on the warning by entering a threshold value below 999999 in the Products.xml messages section. Example:
<Messages>
<ImageQualityHiResWarning>
<Text>Warning: You've added an image with a very high resolution. Cropping or downscaling
will emphasize existing image grain. You may get a better result in an image editor,
using an antialias filter of your choice.
</Text>
<Threshold>600</Threshold>
<MoreInfoURL>http://www.codedcolor.com</MoreInfoURL>
</ImageQualityHiResWarning>
</Messages>
The minimum threshold value is 151, because good quality starts at 150. If the threshold value is set to 150 or less, then the HiRes warning will not be shown. The warning info dialog will only be shown once per session, but the user can use the quality indicator and validator to find those images.
To correct high resolution side effects (grain, color desaturation) to a certain extent, you may also use the Publisher AIE described in the following chapter.