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Merge pull request #89 from pornel/floatq

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Parse quality as float
This commit is contained in:
Josh Aas
2014-08-15 14:18:36 -05:00
parent fc76d48701 5f434e6053
commit d3c8cde986
3 changed files with 22 additions and 15 deletions
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16
jcparam.c
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@@ -151,14 +151,20 @@ jpeg_set_linear_quality (j_compress_ptr cinfo, int scale_factor,
GLOBAL(int)
jpeg_quality_scaling (int quality)
{
return jpeg_float_quality_scaling(quality);
}
GLOBAL(float)
jpeg_float_quality_scaling(float quality)
/* Convert a user-specified quality rating to a percentage scaling factor
* for an underlying quantization table, using our recommended scaling curve.
* The input 'quality' factor should be 0 (terrible) to 100 (very good).
*/
{
/* Safety limit on quality factor. Convert 0 to 1 to avoid zero divide. */
if (quality <= 0) quality = 1;
if (quality > 100) quality = 100;
if (quality <= 0.f) quality = 1.f;
if (quality > 100.f) quality = 100.f;
/* The basic table is used as-is (scaling 100) for a quality of 50.
* Qualities 50..100 are converted to scaling percentage 200 - 2*Q;
@@ -166,10 +172,10 @@ jpeg_quality_scaling (int quality)
* to make all the table entries 1 (hence, minimum quantization loss).
* Qualities 1..50 are converted to scaling percentage 5000/Q.
*/
if (quality < 50)
quality = 5000 / quality;
if (quality < 50.f)
quality = 5000.f / quality;
else
quality = 200 - quality*2;
quality = 200.f - quality*2.f;
return quality;
}