问题
您如何以编程方式准确地确定以设备屏幕尺寸显示相机预览的应用程序的最佳预览尺寸？ (或者在任何可变维度的 View 中，真的)。
在您尝试将此标记为数百万个其他长宽比相关问题之一的重复之前，请理解我正在寻找与一般可用的解决方案不同的解决方案 .我问这个问题是因为我已经阅读了很多“答案”，但它们都指向一个我认为不完整的解决方案(并且可能有缺陷，正如我将在此处描述的那样)。如果这不是缺陷，那么请帮助我理解我做错了什么。
我已经阅读了许多关于应用程序如何选择预览尺寸的不同实现，其中大多数采用了我称之为“足够接近”的方法(您可以根据从屏幕分辨率的比率并找到具有最低值的选项)。这种方法似乎不能确保它选择最好的选项，但可以确保它不会选择最差的选项。
例如，如果我尝试在屏幕分辨率为 720x1184 的设备上迭代每个可用的预览尺寸。并全屏显示预览( 720x1184 )这里是相机预览的结果(按最接近屏幕分辨率的选项排序，格式为 abs(ratio of size option - screen resolution ratio) )。所有尺码均来自 .getSupportedPreviewSizes )。 (“结果”来自使用测试用例的视觉观察，该测试用例使用出现在相机取景器中的静态圆圈并且不是程序化的)
720.0/1184.0 = 0.6081081081081081
Res Ratio Delta in ratios Result
----------------------------------------------------
176/144 = 1.22222222222 (0.614114114114) (vertically stretched)
352/288 = 1.22222222222 (0.614114114114) (vertically stretched)
320/240 = 1.33333333333 (0.725225225225) (vertically stretched)
640/480 = 1.33333333333 (0.725225225225) (vertically stretched)
720/480 = 1.5 (0.891891891892) (vertically stretched)
800/480 = 1.66666666667 (1.05855855856) (looks good)
640/360 = 1.77777777778 (1.16966966967) (horizontally squashed)
1280/720 = 1.77777777778 (1.16966966967) (slight horizontal squash)
1920/1080 = 1.77777777778 (1.16966966967) (slight horizontal squash)
800x1216)800/1216.0 = 0.657894736842
Res Ratio Delta in ratios Results
------------------------------------------------
176/144 = 1.22222222222 (0.56432748538) (looks vertically stretched)
352/288 = 1.22222222222 (0.56432748538) (looks vertically stretched)
480/368 = 1.30434782609 (0.646453089245) (looks vertically stretched)
320/240 = 1.33333333333 (0.675438596491) (looks vertically stretched)
640/480 = 1.33333333333 (0.675438596491) (looks vertically stretched)
800/600 = 1.33333333333 (0.675438596491) (looks vertically stretched)
480/320 = 1.5 (0.842105263158) (looks good)
720/480 = 1.5 (0.842105263158) (looks good)
800/480 = 1.66666666667 (1.00877192982) (looks horizontally squashed)
960/540 = 1.77777777778 (1.11988304094) (looks horizontally squashed)
1280/720 = 1.77777777778 (1.11988304094) (looks horizontally squashed)
1920/1080 = 1.77777777778 (1.11988304094) (looks horizontally squashed)
864/480 = 1.8 (1.14210526316) (looks horizontally squashed)
1.4d 都是可以接受的)将返回 1920x1080如果迭代从最低值到最高值，则在两个设备上。如果迭代从最高值到最低值，它将选择 176x144用于 DeviceA 和 176x144对于 DeviceB。这两个选项(尽管“足够接近”)都不是最佳选择。问题
在研究上述结果时，我如何以编程方式推导出“看起来不错”的值？我无法通过“足够接近”的方法获得这些值，因此我误解了屏幕尺寸、显示预览的 View 和预览尺寸本身之间的关系。我错过了什么？
Screen dimensions = 720x1184
View dimensions = 720x1184
Screen and View Aspect Ratio = 0.6081081081081081
Best Preview Size ratio (720x480) = 1.5
结果令人惊讶，因为其他人似乎都认为最好的选择是计算比率的最小差异，但我所看到的是，最佳选择似乎位于所有选项的中间。并且它们的宽度更接近将显示预览的 View 的宽度。
基于上述观察(最好的选择不是比率最低的值)我开发了这个算法，它迭代所有可能的预览尺寸，检查它是否符合我的“足够接近”标准，存储尺寸满足此标准并最终找到至少大于或等于提供的宽度的值。
public static Size getBestAspectPreviewSize(int displayOrientation,
int width,
int height,
Camera.Parameters parameters,
double closeEnough) {
double targetRatio=(double)width / height;
Size bestSize = null;
if (displayOrientation == 90 || displayOrientation == 270) {
targetRatio=(double)height / width;
}
List<Size> sizes=parameters.getSupportedPreviewSizes();
TreeMap<Double, List> diffs = new TreeMap<Double, List>();
for (Size size : sizes) {
double ratio=(double)size.width / size.height;
double diff = Math.abs(ratio - targetRatio);
if (diff < closeEnough){
if (diffs.keySet().contains(diff)){
//add the value to the list
diffs.get(diff).add(size);
} else {
List newList = new ArrayList<Camera.Size>();
newList.add(size);
diffs.put(diff, newList);
}
Logging.format("usable: %sx%s %s", size.width, size.height, diff);
}
}
//diffs now contains all of the usable sizes
//now let's see which one has the least amount of
for (Map.Entry entry: diffs.entrySet()){
List<Size> entries = (List)entry.getValue();
for (Camera.Size s: entries) {
if (s.width >= width && s.height >= width) {
bestSize = s;
}
Logging.format("results: %s %sx%s", entry.getKey(), s.width, s.height);
}
}
//if we don't have bestSize then just use whatever the default was to begin with
if (bestSize==null){
if (parameters.getPreviewSize()!=null){
bestSize = parameters.getPreviewSize();
return bestSize;
}
//pick the smallest difference in ratio? or pick the largest resolution?
//right now we are just picking the lowest ratio difference
for (Map.Entry entry: diffs.entrySet()){
List<Size> entries = (List)entry.getValue();
for (Camera.Size s: entries) {
if (bestSize == null){
bestSize = s;
}
}
}
}
return bestSize;
}
我看了CommonWares' camera-cwac怎么执行的项目处理这个问题，它似乎也使用“足够接近”算法。如果我将相同的逻辑应用于我的项目，那么我会得到不错但不是“完美”大小的值。我收到
1920x1080返回两个设备。尽管该值不是最差的选择，但它也被略微压扁了。我将在我的测试应用程序中使用测试用例运行他的代码，以确定它是否也会稍微挤压图像，因为我已经知道它会返回一个不是最佳的大小。
最佳答案
Why are the best options not the values that have the lowest delta in ratios?
他们是!但是你需要根据你当前的屏幕方向来计算你的屏幕比例! :)
因此，由于您的设备处于横向模式，第一个表格应如下所示:
1184.0/720.0 = 1.6444444
Res Ratio Delta in ratios Result
----------------------------------------------------
176/144 = 1.222 ( 0.422) (vertically stretched)
352/288 = 1.222 ( 0.422) (vertically stretched)
320/240 = 1.333 ( 0.311) (vertically stretched)
640/480 = 1.333 ( 0.311) (vertically stretched)
720/480 = 1.500 ( 0.144) (vertically stretched)
800/480 = 1.666 (-0.016) (looks good)
640/360 = 1.777 (-0.126) (horizontally squashed)
1280/720 = 1.777 (-0.126) (slight horizontal squash)
1920/1080 = 1.777 (-0.126) (slight horizontal squash)
关于java - 计算最佳相机预览尺寸的正确方法保持纵横比，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28861102/