From ff98c440603e94ae284ad08d289418f4b5cca89e Mon Sep 17 00:00:00 2001 From: aavit Date: Tue, 14 Oct 2014 12:18:08 +0200 Subject: Doc: Improved explanation of quality setting in QImageReader/Writer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Explanation was somewhat inprecise and incomplete. Task-number: QTBUG-41358 Change-Id: Iae52c30868ca48a49eac76d6979a9b02c24a7d49 Reviewed-by: Topi Reiniö --- src/gui/image/qimagereader.cpp | 23 +++++++++++++++-------- src/gui/image/qimagewriter.cpp | 17 ++++++++++------- 2 files changed, 25 insertions(+), 15 deletions(-) diff --git a/src/gui/image/qimagereader.cpp b/src/gui/image/qimagereader.cpp index a1b9743209..a7a08a6fee 100644 --- a/src/gui/image/qimagereader.cpp +++ b/src/gui/image/qimagereader.cpp @@ -877,15 +877,22 @@ QString QImageReader::fileName() const /*! \since 4.2 - This is an image format specific function that sets the quality - level of the image to \a quality. For image formats that do not - support setting the quality, this value is ignored. + Sets the quality setting of the image format to \a quality. - The value range of \a quality depends on the image format. For - example, the "jpeg" format supports a quality range from 0 (low - quality, high compression) to 100 (high quality, low compression). + Some image formats, in particular lossy ones, entail a tradeoff between a) + visual quality of the resulting image, and b) decoding execution time. + This function sets the level of that tradeoff for image formats that + support it. - \sa quality() + In case of scaled image reading, the quality setting may also influence the + tradeoff level between visual quality and execution speed of the scaling + algorithm. + + The value range of \a quality depends on the image format. For example, + the "jpeg" format supports a quality range from 0 (low visual quality) to + 100 (high visual quality). + + \sa quality() setScaledSize() */ void QImageReader::setQuality(int quality) { @@ -895,7 +902,7 @@ void QImageReader::setQuality(int quality) /*! \since 4.2 - Returns the quality level of the image. + Returns the quality setting of the image format. \sa setQuality() */ diff --git a/src/gui/image/qimagewriter.cpp b/src/gui/image/qimagewriter.cpp index d172d4008f..fa261df1a5 100644 --- a/src/gui/image/qimagewriter.cpp +++ b/src/gui/image/qimagewriter.cpp @@ -434,13 +434,16 @@ QString QImageWriter::fileName() const } /*! - This is an image format specific function that sets the quality - level of the image to \a quality. For image formats that do not - support setting the quality, this value is ignored. + Sets the quality setting of the image format to \a quality. - The value range of \a quality depends on the image format. For - example, the "jpeg" format supports a quality range from 0 (low - quality, high compression) to 100 (high quality, low compression). + Some image formats, in particular lossy ones, entail a tradeoff between a) + visual quality of the resulting image, and b) encoding execution time and + compression level. This function sets the level of that tradeoff for image + formats that support it. For other formats, this value is ignored. + + The value range of \a quality depends on the image format. For example, + the "jpeg" format supports a quality range from 0 (low visual quality, high + compression) to 100 (high visual quality, low compression). \sa quality() */ @@ -450,7 +453,7 @@ void QImageWriter::setQuality(int quality) } /*! - Returns the quality level of the image. + Returns the quality setting of the image format. \sa setQuality() */ -- cgit v1.2.3