diff --git a/cgCompress.pro b/cgCompress.pro
index 0daf472..4c861eb 100644
--- a/cgCompress.pro
+++ b/cgCompress.pro
@@ -4,11 +4,11 @@ INCLUDEPATH += .
 CONFIG += console
 QT += concurrent
 
-LIBS += -lz
+LIBS += -lz -llz4
 
 # Input
-HEADERS += src/Image.hpp src/Frame.hpp src/ImageSimilarities.hpp src/MultiImage.hpp src/Converter.hpp src/OraSaver.hpp src/FileUtils.hpp src/Format.hpp src/ProgressBar.hpp
-SOURCES += src/Image.cpp src/Frame.cpp src/ImageSimilarities.cpp src/MultiImage.cpp src/Converter.cpp src/OraSaver.cpp src/FileUtils.cpp src/Format.cpp src/main.cpp
+HEADERS += src/Image.hpp src/Frame.hpp src/ImageSimilarities.hpp src/MultiImage.hpp src/Converter.hpp src/OraSaver.hpp src/FileUtils.hpp src/Format.hpp src/FileSizeEval.hpp src/ProgressBar.hpp
+SOURCES += src/Image.cpp src/Frame.cpp src/ImageSimilarities.cpp src/MultiImage.cpp src/Converter.cpp src/OraSaver.cpp src/FileUtils.cpp src/Format.cpp src/FileSizeEval.cpp src/main.cpp
 
 # minizip
 SOURCES += src/minizip/ioapi.cpp src/minizip/zip.cpp
diff --git a/src/FileSizeEval.cpp b/src/FileSizeEval.cpp
new file mode 100644
index 0000000..82bbaaa
--- /dev/null
+++ b/src/FileSizeEval.cpp
@@ -0,0 +1,112 @@
+/*
+	This file is part of cgCompress.
+
+	cgCompress is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	cgCompress is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with cgCompress.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "FileSizeEval.hpp"
+#include "SubQImage.hpp"
+
+#include <lz4.h>
+#include <lz4hc.h>
+
+
+static int compressed_lz4_size( const std::vector<uint8_t>& data ){
+	auto max_size = LZ4_compressBound( data.size() );
+	std::vector<uint8_t> buffer( max_size );
+	
+	return LZ4_compress_HC(
+			(const char*)data.data(), (char*)buffer.data()
+		,	data.size(), buffer.size()
+		,	LZ4HC_DEFAULT_CLEVEL //TODO: Higher?
+		);
+}
+
+
+int FileSize::simple_alpha( QImage mask, int transparent ){
+	//TODO:
+	return 0;
+}
+
+/** Calculates the sum of the absolute difference between touching pixels
+ *  
+ *  \param [in] img Image to calculate for
+ *  \return The computed value
+ */
+int FileSize::image_gradient_sum( QImage img ){
+	int diffs = 0;
+	
+	auto w = img.width();
+	for( int iy=0; iy<img.height(); iy++ ){
+		auto row = (const QRgb*) img.constScanLine( iy );
+		for( int ix=1; ix<w/*img.width()*/; ix++ ){
+			//we add the difference in shown pixels
+			QRgb left = row[ix-1], right = row[ix];
+			diffs += abs( qAlpha(left) - qAlpha(right) );
+			if( ( qAlpha(left) > 0 ) && ( qAlpha(right) > 0 ) ){
+				diffs += abs( qRed(left) - qRed(right) );
+				diffs += abs( qGreen(left) - qGreen(right) );
+				diffs += abs( qBlue(left) - qBlue(right) );
+			}
+		}
+	}
+	
+	return diffs;
+}
+
+int FileSize::image_gradient_sum( const SubQImage& img, QImage mask, int pixel_different ){
+	int diffs = 0;
+	
+	auto w = img.width();
+	for( int iy=0; iy<img.height(); iy++ ){
+		auto row_alpha = mask.constScanLine( iy );
+		auto row = img.row( iy );
+		for( int ix=1; ix<w; ix++ ){
+			auto alpha_left  = row_alpha[ix-1] != pixel_different;
+			auto alpha_right = row_alpha[ix  ] != pixel_different;
+			diffs += (alpha_left != alpha_right) ? 255 : 0;
+			//TODO: not great for images with transparency
+			//we add the difference in shown pixels
+			if( !(alpha_left || alpha_right) ){
+				QRgb left = row[ix-1], right = row[ix];
+				diffs += abs( qRed(  left) - qRed(  right) );
+				diffs += abs( qGreen(left) - qGreen(right) );
+				diffs += abs( qBlue( left) - qBlue( right) );
+			}
+		}
+	}
+	
+	return diffs;
+}
+
+int FileSize::lz4compress_size( QImage img ){
+	std::vector<uint8_t> data;
+	data.resize( img.width() * img.height() * 4 );
+	
+	//Encode data
+	for( int iy=0; iy<img.height(); iy++ ){
+		auto row = (const QRgb*) img.constScanLine( iy );
+		for( int ix=0; ix<img.width(); ix++ ){
+			auto pos = iy*img.width()*4 + ix*4;
+			data[ pos + 0 ] = qRed(   row[ix] );
+			data[ pos + 1 ] = qGreen( row[ix] );
+			data[ pos + 2 ] = qBlue(  row[ix] );
+			data[ pos + 3 ] = qAlpha( row[ix] );
+		}
+	}
+	
+	//Compress
+	auto size = compressed_lz4_size( data );
+	return size;
+}
diff --git a/src/FileSizeEval.hpp b/src/FileSizeEval.hpp
new file mode 100644
index 0000000..3f614f3
--- /dev/null
+++ b/src/FileSizeEval.hpp
@@ -0,0 +1,40 @@
+/*
+	This file is part of cgCompress.
+
+	cgCompress is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	cgCompress is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with cgCompress.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef FILE_SIZE_EVAL_HPP
+#define FILE_SIZE_EVAL_HPP
+
+#include <QImage>
+
+/**
+	Several methods to guess how much space a image will take to store compressed.
+	However they are not compariable with final filesize or another metric
+*/
+
+class SubQImage;
+
+namespace FileSize{
+
+int simple_alpha( QImage mask, int transparent );
+int image_gradient_sum( QImage img );
+int image_gradient_sum( const SubQImage& img, QImage mask, int pixel_different );
+int lz4compress_size( QImage img );
+
+}
+
+#endif
+
diff --git a/src/Format.cpp b/src/Format.cpp
index 204e81c..e8a859f 100644
--- a/src/Format.cpp
+++ b/src/Format.cpp
@@ -16,34 +16,10 @@
 */
 
 #include "Format.hpp"
+#include "FileSizeEval.hpp"
 
 #include <QBuffer>
 
-/** Calculates the sum of the absolute difference between touching pixels
- *  
- *  \param [in] img Image to calculate for
- *  \return The computed value
- */
-int image_gradient_sum( QImage img ){
-	int diffs = 0;
-	
-	auto w = img.width();
-	for( int iy=0; iy<img.height(); iy++ ){
-		auto row = (const QRgb*) img.constScanLine( iy );
-		for( int ix=1; ix<w/*img.width()*/; ix++ ){
-			//we add the difference in shown pixels
-			QRgb left = row[ix-1], right = row[ix];
-			diffs += abs( qAlpha(left) - qAlpha(right) );
-			if( ( qAlpha(left) > 0 ) && ( qAlpha(right) > 0 ) ){
-				diffs += abs( qRed(left) - qRed(right) );
-				diffs += abs( qGreen(left) - qGreen(right) );
-				diffs += abs( qBlue(left) - qBlue(right) );
-			}
-		}
-	}
-	
-	return diffs;
-}
 
 /** Compress image to a memory buffer
  *  
@@ -66,7 +42,7 @@ QByteArray Format::to_byte_array( QImage img ) const{
  */
 int Format::file_size( QImage img, Precision p ) const{
 	if( precision_level > 0 && p != HIGH )
-		return image_gradient_sum( img );
+		return FileSize::image_gradient_sum( img );
 	return to_byte_array( img ).size();
 }
 
diff --git a/src/Image.cpp b/src/Image.cpp
index 3d63e2a..f25341a 100644
--- a/src/Image.cpp
+++ b/src/Image.cpp
@@ -16,6 +16,7 @@
 */
 
 #include "Image.hpp"
+#include "FileSizeEval.hpp"
 
 #include <cmath>
 
@@ -408,28 +409,9 @@ int Image::compressed_size( Format format, Format::Precision p ) const{
 int Image::estimate_compressed_size( Format format ) const{
 	if( mask.isNull() )
 		return format.file_size( remove_transparent(), Format::LOW );
-	int diffs = 0;
 	
-	auto w = img.width();
-	for( int iy=0; iy<img.height(); iy++ ){
-		auto row_alpha = mask.constScanLine( iy );
-		auto row = img.row( iy );
-		for( int ix=1; ix<w; ix++ ){
-			auto alpha_left  = row_alpha[ix-1] != PIXEL_DIFFERENT;
-			auto alpha_right = row_alpha[ix  ] != PIXEL_DIFFERENT;
-			diffs += (alpha_left != alpha_right) ? 255 : 0;
-			//TODO: not great for images with transparency
-			//we add the difference in shown pixels
-			if( !(alpha_left || alpha_right) ){
-				QRgb left = row[ix-1], right = row[ix];
-				diffs += abs( qRed(  left) - qRed(  right) );
-				diffs += abs( qGreen(left) - qGreen(right) );
-				diffs += abs( qBlue( left) - qBlue( right) );
-			}
-		}
-	}
-	
-	return diffs;
+	return FileSize::image_gradient_sum( img, mask, PIXEL_DIFFERENT );
+	return FileSize::lz4compress_size( remove_transparent() );
 }
 
 bool Image::mustKeepAlpha() const{